Geomorphology

the origin and evolution of Earth in this chapter we will read about the story of
the origin that is the formation of Earth and evolution that is how Earth evolved
over time meaning what were the physical changes that the Earth went
through now the origin of Earth has two theories basically the early and
modern theories

Nebular Hypothesis
Many hypotheses were recommended by various philosophers and scientists regarding
the origin of the Earth, and one of the earlier and popular arguments was made by a
German philosopher named Emmanuel Kant. Later on, a mathematician named
Laplace revised it in 1796. To understand this theory, I recommend that you go with
this order. First, everything, right from the Sun, planets, stars, asteroids—everything
has been created from a nebula cloud. Second, stars were formed way before planets
and asteroids came into existence. Planets are somewhere around 4.5 billion years
old, and most stars are between 1 billion to 10 billion years old. The Sun is the biggest
star in the universe, remember that. So, what happened was initially there was this
nebula cloud, which was made of helium, hydrogen, and other sorts of dust particles.
This cloud started rotating very heavily, and due to that, most of the hydrogen and
helium elements came to the center and started colliding with each other. Due to the
friction and collision of particles, a fusion reaction took place, and pure energy started
generating. This created the Sun, the biggest star in our universe. Now it is time for
the planets to arrive. We know that hydrogen and helium are low-density elements,
and they moved to the center forming the Sun, so it is very logical that if lighter
elements went to the center, the heavier ones would go away from the center, right?
And that's what happened. The heavier elements like carbon, oxygen, nitrogen, iron,
phosphorus, silicon, etc., moved away from the center. If you see, the Earth and all
other planets are made out of denser elements than stars. Then these heavier
elements started forming small clumps of clouds like smaller nebulas. With further
rotation, friction, and collision of particles, it led to the formation of a disc-shaped
cloud, and the planets were formed through the process of accretion. Because now the
heavy elements will come to the center, and layer by layer, planets started forming.
So, this was the earlier theory of the origin of Earth, which is also known as the
Nebular Hypothesis.

Big Bang Theory

Essentially, it is an effort to explain what happened at the very beginning of our

universe. Many discoveries in astronomy and physics have shown beyond a
reasonable doubt that our universe did, in fact, have a beginning. Prior to that
moment, there was nothing; during and after that moment, there was

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something—that is, the universe. The Big Bang Theory is an attempt to explain
what happened during and after that moment.

In 1920, Edwin Hubble provided evidence that the universe is expanding. Edwin
Hubble is the same scientist after whom the famous Hubble Space Telescope is
named. He stated that as time passes, galaxies move further and further apart.
There is an experiment associated with this concept—take a balloon and mark
some points on it to represent galaxies. Now, if you start inflating the balloon,
the points marked on it will appear to be moving away from each other as the
balloon expands. Similarly, the distance between galaxies is also found to be
increasing, leading to the conclusion that the universe is expanding. However,
it is important to note that, unlike the points on the balloon, which themselves
expand, galaxies do not actually expand. Scientists do not have real evidence
of galaxies themselves expanding, but they do believe that the distance
between galaxies is increasing. Hence, the balloon example is only partially
correct.

The Big Bang Theory considers the following stages in the development of the
universe. In the beginning, all matter forming the universe existed in one place
in the form of a tiny ball—a singular atom—with an unimaginably small volume,
infinite temperature, and infinite density. However, where did this singularity
come from? Scientists do not know. Why did it appear? That too remains
unknown. It is thought to exist at the core of black holes, which are areas of
intense gravitational pressure. The pressure is believed to be so extreme that
finite matter is compressed into infinite density—a concept that is purely
mathematical and difficult to comprehend.

In the second stage, this tiny ball exploded violently, leading to a huge
expansion. The universe, as we know it, was born. Time, space, and matter all
began with the Big Bang. In just a fraction of a second, the universe expanded
from being smaller than a single atom to being larger than a galaxy, and it
continued to grow at an astonishing rate. It is still expanding today. Scientists
generally agree that the Big Bang took place around 13.7 billion years ago.

Within the first second of the Big Bang, some energy was converted into matter
and antimatter. These two opposite types of particles largely destroyed each
other, but some matter survived. More stable particles, called protons and
neutrons, started forming. Protons are positively charged, while neutrons are
negatively charged particles. Over the next three minutes, the temperature
dropped below 1 billion degrees Celsius, which allowed protons and neutrons to
come together and form hydrogen and helium nuclei. After 300,000 years, the
universe had cooled to about 4,000 degrees, allowing atomic nuclei to capture
electrons and form fully-fledged atoms. At this stage, the universe became

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transparent and was filled with clouds of hydrogen and helium gas. This is the
story of the universe, otherwise known as the Big Bang Theory.

The expansion of universe means increase in space between the galaxies

always remember this order a universe consists of more than one Galaxy and
one Galaxy consists of moons asteroids planets and stars so the solar system
that we are part of is one Galaxy like that there are many other galaxies and
the name of a galaxy is Milky Way though we know there are many other
galaxies but we do not know whether there is another universe so the scientific
Community only believes in the theory that the universe is expanding

formation of stars
the formation of stars is believed to have taken place some 5 to 6 billion years
ago. Earth is believed to be 4.6 billion years old, so clearly, stars were there
before the planets.

Previously, we spoke about how matter and energy were scattered in the
universe due to the big explosion of the singular atom. One thing to know is
that the matter and energy were uneven, meaning there were differences in
the densities in every matter. Because of that, there was attraction between
these matters, and that's how hydrogen and helium atoms were formed.

Basically, hydrogen and helium are gases. Like this, there are many tiny groups
of hydrogen and helium gases constantly colliding with each other and
producing energy. This process is also called a fusion reaction, where two
light nuclei combine together, releasing a vast amount of energy. And this
energy gave rise to the formation of stars.

formation of planets
Now we are going to talk about the formation of planets now there are again
some stages in the development of planets as well so let's go through them so
just moments back we have read that stars are localized lump of gases now the
gravitational force within those lump leads to the formation of a core to the gas
cloud and a huge rotating disc of gas and dust envelopes around the gas core
so let me just show it to you with the help of an illustration because it's very
difficult to make you understand with words so a good example to illustrate this
is uh take a bucket of water a little water not much and put some sand in it
now spin the water in that bucket in a circular fashion soon you'll notice that so
all the mud particle that you had poured it will come in the center and gather
so that's how it forms a core and the same thing happens in these gas clouds
inside a star and then after a long time layers of of layers starts forming and
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that's how a rotating dis of gas is formed and then in the next stage the gas
cloud starts getting condensed meaning it gets very concentrated and due to
this phenomena the matters that are around the core develops into small
rounded objects then again after time what happens these small objects by the
process of cohesion meaning they form group sort of a thing and develops into
what is called Planet decimal so you see most of the things happen because of
collision and gravitational attraction because of these phenomena the
materials stick together and that's what makes these large number of small
bodies now in the final stage these large number of small bodies they accrete
to form a few larger bodies so the meaning of accrete is forming layer after
layer so these smaller bodies that were formed due to Collision and
gravitational attraction with time what happens is layers several layers are
formed on it as a result from a small body it becomes a large body and that's
how planets are formed

our solar system

So here it says our solar system consists of nine planets now this is a fairly old
book so as of now there are eight planets in the solar system so that means
Pluto is no longer a planet and the reason behind that is because it has been
classified as dwarf so the meaning of dwarf planet is it is a round mass of metal
and rock or gas moving around the Sun that is not large enough to be
considered as as a planet okay some of the dwarf planet in our solar system
includes Pluto then we have Ceres and Eris so as I've told you before that
everything right from planets and stars and everything has been formed out of
this Cloud called nebula so the core formation of this nebula started somewhat
around 5 to 5.6 billion years ago and the planets were formed about 4.6 billion
years ago so clearly it means that stars were there before planets now don't
forget this just remember this our solar system consists of Sun that is the star
Sun is a star basically and then we have eight planets then 63 moons then
millions of smaller bodies like asteroids and comets and huge quantity of dust
grains and gases and if you see it is because of these two last terms that is
dust grains and gases there are new stars and planets that are coming up so
there's always a new discovery by NASA about all these planets and stars so
out of the eight planets Mercury Venus Earth and Mars are called as the inner
planet so if you look at the solar system after Mars the Jupiter planet comes
and in between Mars and Jupiter there is a big asteroid belt so those planets
which are out of asteroid belt including Jupiter they are known as outer planets
and those which are inside they are called inner planets so these planets which

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are inside the asteroid belt they are called as terrestrial planets meaning they
have earthlike similarities in other words they consist of rock and metals and
the planets that are outside the asteroid belt they are called Jovian or gas giant
planets so basically they are like Jupiter and they are huge planets but they
have very thick atmosphere mostly of helium and hydrogen and this is another
cool fact all the planets were formed in the same period sometime about 4.6
billion years ago so when we hear something like this that all the planets were
formed in the same period it clearly proves the fact that whatever phenomena
that caused these planets to exist is actually true which is the Big Bang Theory
the universe being expanding while a Theory because just for argument sake
had it been the fact that all the planets came into existence at their own time
then it would be difficult to argue that what actually happened because there
there's going to be very different kind of data of you know something
happened because of something else and then something happened because
of something else if everything happens because of one reason then it is easier
to study and understand

what is the difference between terrestrial

and Jovian Planets
So let me quickly tell you this terrestrial planets are those planets which are in
between the Sun and the asteroid belt and the ones that are outside the
asteroid belt they are known as Jovian planets or outer planets so as we know
that most of the terrestrial planets are full of rock and so that means it has very
less gas and dust and if you look at the Jovian planets they have a lot of gas
present dust and gas present so the theory goes like this Newton realized that
the reason the planets orbit around the Sun is related to why objects fall to
Earth when we drop them the Sun's gravity pulls on the planets just as Earth's
gravity pulls down anything that is not held up by some other force and keeps
you and me on the ground so heavier the objects produce a bigger
gravitational pull than lighter ones so as the heavy weight in our solar system
the Sun is the strongest gravitational pull now with this theory you know that
the terrestrial planets which are between the Sun and asteroid belt they are
nearer to the Sun and because of that they exert a lot of gravitational pull and
because they are nearer to the Sun meaning the heat of the Sun blew away all
the gases and dust but then the Jovian planets which are outside the asteroid
belt they are far away from the Sun so the solar winds were not that intense
that's why these planets still have a lot of gas and dust particles so that's the
reason between the inner planets and the outer planets or in other words the
terrestrial planets and the Jovian planets
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the moon
Now we're going to talk about the moon. Moon is the only natural satellite of
the Earth, meaning Moon just revolves around the Earth. Now there is a theory
behind how the Moon was formed. So in 1838, Sir George Darwin suggested
that the Earth and the Moon were combined, okay, they were joined together
like a dumbbell shape. So if you have seen a dumbbell, it looks like this. Now
what happened was it eventually broke, and the material that was forming the
Moon got separated from the Earth. To support this theory, Darwin went on to
say that if you look at the depression in the Pacific Ocean—so the Pacific Ocean
is the largest and the deepest ocean—the depression that occupies the Pacific
Ocean is due to the separation of the Moon object from the Earth. So this is the
theory of George Darwin.

Now, the present scientists do not accept this theory. What we now believe is
that the formation of the Moon as a satellite of Earth is an outcome of a giant
impact. Now, this theory has another name, which is called the Big Splat. Now,
Big Splat means Big Splash, a giant impact. Now, what this theory says is that
there was an object the size of Mars. So that object, that body, collided into the
Earth sometime shortly after the Earth was formed. So when two objects
collide, there are these debris. These portions of small blasted material
continued to orbit around the Earth, and due to gravitational attraction and
collision, these small particles eventually formed into the present Moon. So this
theory is now widely accepted about the origin of the Moon.

the evolution of the earth

So once upon a time, the planet Earth was a barren, rocky, and hot object with
a thin atmosphere of hydrogen and helium. Today, when we see a picture of the
Earth, it does not look like that. So obviously, there must have been some
events, some processes that caused this change. Let’s go ahead and
understand what led to the evolution of life on the surface of the planet.

We know that all celestial bodies were formed through a process called
accretion, meaning layer after layer after layer, gradually growing from a small
body to a large body. Similarly, Earth is no different. The Earth has a layered
structure, so from the outermost end of the atmosphere to the center of the
Earth, the material that exists is not uniform, meaning they are not the same.
As we move from the outermost layers of the Earth towards its interior, the
density increases.

That’s why we also know that there are five layers in the atmosphere, and we
also know that the Earth's interior is divided into four parts: the crust, mantle,
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outer core, and inner core. This is why, in geography, we have different
disciplines to understand the Earth. We have the lithosphere, which deals with
the solid outer part, the atmosphere, which studies the gases surrounding the
planet, and the hydrosphere, which focuses on water bodies. These aspects
have been nicely categorized into different subjects so that we can study Earth
in a much better and systematic way.

lithosphere
When we hear the word lithosphere, it refers to the outer layer of the Earth,
consisting of the crust and the upper part of the mantle. Initially, the Earth
was in a volatile state, meaning constant and rapid changes were taking
place. The particles that formed the Earth were undergoing continuous
collisions, increasing density, energy, and temperature.

In chemistry, when metals are extracted or refined, they are placed in a

furnace at extremely high temperatures to melt them and separate their
properties. A similar process occurred during Earth's formation. When the
temperature was extremely high, all materials inside the Earth started
separating based on their densities:

Heavy materials like iron sank toward the center of the Earth, forming the
core.
Lighter materials moved toward the surface, eventually forming the crust.
As time passed, the Earth cooled down, and the outer layer solidified to form
the crust. But then came another major event—the giant impact that led to
the formation of the Moon. This collision further heated the Earth, reinforcing
the separation of materials into different layers.

Today, we know that Earth has four main layers:

1. Crust – The outermost solid layer.

2. Mantle – A semi-solid layer beneath the crust.
3. Outer core – A liquid layer composed mainly of iron and nickel.
4. Inner core – A solid, dense center of iron and nickel.
One key fact to remember: From the crust to the core, the density of
materials increases.

the evolution of atmosphere and

hydrosphere
so there are three stages in the evolution of the present atmosphere it is
because of these three stages the present atmosphere came into being so in
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the premod atmosphere the Sun and its planet formed about 5 billion years ago
where there was an explosion of a supernova which is a big star so that before
bursting had generated heavy elements starting from hydrogen and helium so
that was the first stage of the present atmosphere I mean to say atmosphere
initially looked like that and then comes the second stage we have read that
the Earth was a very volatile object there were constant changes rapid
development was going on and the temperature was so high that the interior of
the Earth was super hot so when an object is super hot it will emit heat which is
also called as thermal radiation so we have to say that these thermal radiation
they will also contribute to the evolution of the atmosphere so every single
aspect together contributed towards present atmosphere that's why we have to
count every single thing and now comes the final stage that is the third stage
today when human beings and living organism came into existence in this
world there was a process called photo synthesis so photosynthesis is a
chemical process through which plants some bacteria and algae produce
glucose and oxygen from carbon dioxide and water using only light as a source
of energy before even humans arrived on this planet There Were Trees plants
and all sorts of grasses and Etc so we can say that the process of
photosynthesis has already begun before the humans arrived and we know that
plants take carbon dioxide and emits oxygen so again there is a emission of
oxygen involved and that is the final and the third stage of the composition of
present atmosphere always remember the premod atmosphere which is the
initial atmosphere when the Earth was beginning to form that atmosphere
consisted only of hydrogen and helium so that atmosphere went away and the
reason behind that is because it is not just Earth all the terrestrial planets so
we have spoken about what the terrestrial planets are these are the planets
that are in between Sun and and the asteroid belt so basically there are only
four planets Mercury Venus Earth and Mars now these planets the terrestrial
planets since they are closer to the Sun these planets received a lot of solar
wind coming from the Sun it stripped off the hydrogen and helium atmosphere
and that's why these planets don't look like the jovial planets the planets which
are outside the asteroid belt and finally when the Earth was cooling down the
gases and the water vapor they were released from the interior of Earth now
this thing is very easy to imagine whenever you're trying to boil water in an
utensil at your place you will see that if you put a cover on it or if you put some
kind of a plate on it you'll see that the plate will gather all the water vapor so
the similar thing happened when the Earth was cooling down all the heat was
released upward and in the atmosphere the water vapor was collected and that
is how the present atmosphere started the early atmosphere largely contained
water vapor nitrogen carbon dioxide methane ammonia and very little of free
oxygen so the process through which the gases were outpoured from the
interior is called degassing now you must be wondering that okay the gases

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were degased so how did it still continue to form water vapor and the answer
to that question is the continuous volcanic eruption so volcanoes are like a
ventilator of the earth so from these ventilators the inner core the heated
substance of the earth starts pouring out and again if there is a a substance
which has a high temperature there will be heat and because of this continuous
volcanic eruption there was a lot of water vapor and gases generated and as
these water vapor were released they started getting condensed and then the
carbon dioxide in the atmosphere got dissolved in rain water and the
temperature further decreased causing more condensation and rain and then
once rain started happening the rain water falling onto the surface got
collected in the depression to give rise to oceans and that's how the ocean
iodes of the earth were formed so these Earth's ocean were formed within 500
million years from the formation of the earth now that tells us that the oceans
are as old as 4,000 million years and then once the oceans were formed life
began to evolve and if you notice bacteria were among the first life forms to
appear on Earth and if you see humidity is perfect for any bacterial growth and
humidity is formed due to heat and water hence it is obvious that once the
oceans were formed life began to evolve and once life began to evolve the
process of photosynthesis also started so for a very long time life was confined
to the oceans that means there was no presence of life on a land form it was
only confined to Ocean because ocean had the perfect combination of oxygen
through the process of photosynthesis and eventually this big ocean was
saturated with oxygen and after that oxygen began to flood to the atmosphere
and that's how oxygen contain started increasing in the atmosphere

origin of life
because once the earth was formed it is necessary to know about the life on
Earth otherwise the entire big picture is incomplete that's why the origin and
evolution of life is regarded as the last phase in the evolution of Earth so far
after reading all of this we are clear about the fact that initially it was
impossible to live on Earth because the conditions were not ideal you know
Earth was w vertile it was super hot there was very little oxygen so all these
things were going on hence the modern scientist they think that the origin of
life is due to the complex chemical reaction that generated complex organic
molecules and because of their assembly we came into present and this
assembly of complex organic molecules is such that it duplicates themselves it
is just like amoeba how it splits into two equal copies of itself similarly this
organic molecule it started copying itself and that got converted into inanimate
matter and that converted some matters which were lifeless which had no sign
of life into living organism so when you look at a rock you'll find fossils in it
fossils are the dead decay of animals and plant organism hence when we look

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at a rock the record of life that existed on this planet can be seen across
different periods so when you look at Blue algae which is found in lakes and
water bodies and if you look at the microscopic structure closely you will find
that these formations are present in rocks that are much older and are some
300,000 million years ago and that is how we can assume that life began to
evolve sometime 3,800 million years ago and if you want to know how a
unicellular bacteria turned into a modern man then you have to look at this
geological time scale so this geological time scale shows some life major
events and it is very fascinating to see how this thing happened it is almost like
a magic but there's a huge deep science involved and that is why it makes
geography interesting you know I'm so fascinated to read all of this maybe I
will make a separate short videos on these smaller Concepts as to how human
came into existence how Earth was formed how this ocean were formed moon
were formed Etc anyways with this we have come to an end of this chapter and
this chapter has been a real eye opener till now for me and it's so interesting
and fascinating to read this I hope you understood whatever that I told you
though in between it was kind of difficult for me to comprehend because the
words that were used they were not very simple to be able to convert them
into a real metaphor or a simpler

Distribution of oceans and continents

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Today, continents cover 29% of the total surface of the Earth, while
the remaining 71% is covered by ocean bodies. This is the reason
why planet Earth is also called the "Blue Planet.”

Continental drift theory

Alfred Wegener's **Continental Drift Theory** proposed that all continents were
once part of a single supercontinent called **Pangaea** (meaning "all earth"),
surrounded by a vast ocean, **Panthalassa** ("all water"). Around **200 million
years ago**, Pangaea split into two landmasses: **Laurasia** in the north and
**Gondwanaland** in the south. These later fragmented into the continents we
see today.

Wegener's theory was based on the observation that the coastlines of

continents, especially those across the **Atlantic Ocean**, fit together like
puzzle pieces. This idea was first noted by Dutch mapmaker **Abraham
Ortelius**, but in **1912**, German meteorologist **Alfred Wegener** provided
a scientific explanation, suggesting that continents are **slowly drifting apart**
over time.

Forces Behind the Continental Drift Theory

Alfred Wegener proposed two forces responsible for continental drift:

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 1. Pole-Fleeing Force – Wegener suggested that Pangaea originally formed
near the South Pole, and the Earth’s centrifugal force caused the
landmass to drift towards the Equator.
2. Tidal Force – He believed that the gravitational pull of the Moon and the
Sun created tidal forces strong enough to move continents over millions of
years.
However, most scholars found these forces inadequate to explain continental
movement. Due to the lack of strong scientific evidence, Wegener’s
Continental Drift Theory was eventually rejected.

Post-Drift Studies: Advancements After Wegener's Theory

After Wegener’s Continental Drift Theory was rejected, scientists conducted

further research to explore geological processes in more depth. The main
drawback of Wegener’s theory was that his evidence was limited to
landmasses, while the ocean floor remained largely unexplored.

Key Developments in Post-Drift Studies:

1. Ocean Floor Mapping (Post-World War I)

Technological advancements after World War I helped in detailed

ocean floor mapping.
These studies provided fresh insights into the distribution of
continents and oceans.
2. Convectional Current Theory (1930, Arthur Holmes)

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 1.
Holmes proposed that convection currents in the mantle drive the
movement of the Earth's crust.
The upper mantle (asthenosphere) is weak due to molten rock
moving in a circular motion (hot material rises, cool material sinks).
These mantle convection currents later became the foundation for
Plate Tectonics Theory, which eventually replaced Continental
Drift Theory.
Thus, post-drift studies helped refine our understanding of how continents
move, leading to the modern Plate Tectonics Theory that explains the
distribution of landmasses and oceanic features more accurately.

Mapping of the Ocean Floor

As the name suggests, mapping the ocean floor refers to the study and
exploration of the ocean bed. Scientists discovered that the ocean floor is not
just a vast, flat plain but has a diverse and uneven surface, similar to
land. It contains mountain ranges, deep trenches, and valleys. Trenches
are deep cavities or cracks in the ocean bed, usually formed when two

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continental plates move apart. Another important feature is the Mid-
Oceanic Ridge, which is a long underwater mountain range.

The formation of these ridges is due to volcanic eruptions. Beneath the

Earth’s crust lies the mantle, which consists of molten rock in continuous
motion. This makes the mantle an unstable layer. When a volcanic
eruption occurs, magma rises through the oceanic crust, cools down,
and solidifies into new oceanic crust. Over time, the repeated eruption and
solidification create the oceanic ridge, an uplifted landmass resembling a
mountain range.

To confirm this process, scientists collected rock samples from both the ridge
area and the continental region to compare their ages. The results showed
that the rocks from the ridge area were younger, proving that newer
molten rocks are constantly forming layers of oceanic crust. This
significant discovery added strong evidence to post-drift studies, making
them more scientifically valid.

Ocean floor configuration is the division of the ocean floor into three
segments based on depth and relief. The first segment is the
Continental Margin, which is the area between the continental shore
and the deep-sea basin. If you are on a beach and move further
towards the sea, you will notice the landform shows depression,
causing the water level to increase. Eventually, the water gets
really deep, appearing dark blue from above, marking the deep-sea
basin. This area is called the Continental Margin and consists of the
continental shelf, continental slope (land depression), continental
rise, and deep oceanic trenches. Trenches are deep cavities that
occur when two continental plates move apart. The second segment
is the Abyssal Plains, which are extremely deep plains lying
between the continental margin and mid-oceanic ridges. These
areas serve as natural depositories for sediments like mud and rock
particles that gradually move downward due to the ocean floor's
depression. The third segment is the Mid-Oceanic Ridges, which are
long chains of mountain systems beneath the ocean and are the
longest mountain chains on Earth. These ridges form due to intense
volcanic activity when magma from the mantle breaks through the

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oceanic crust, cools, and forms new layers, creating an uplifted
landmass that appears as a ridge.

The distribution of earthquakes and volcanoes can be understood

through various indicators. The big black dots on the map represent
hot spots, which are locations where magma rises from the mantle,
forming volcanic activity. Many of these hot spots are found on the
ocean floor, while a few exist on continental landmasses. The tiny
black dots indicate places where volcanoes are present, with a
majority located on continents and a few on the ocean floor.
Additionally, tiny gray dots forming long lines represent regions of
shallow earthquakes, primarily found along mid-oceanic ridges,
which result from the movement of continental plates. Earthquakes
are tremors originating from such plate movements. Lastly, the
gray-shaded regions denote deep earthquake zones, which are also
part of mid-oceanic ridges but are much deeper and highly active
earthquake zones. A notable example is the Indian Himalayan
region, where the Indian and Eurasian plates are constantly

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converging, creating immense tectonic tension and instability.

now we go on to the topic concept of seafloor spreading now this is

where things get really interesting so you remember Alfred
Wagner's continental drift theory in case you haven't seen the video
I recommend you do so the video link is in the description or you
can also click on the info card on top vag's Theory focused more on
the Continental evidence like the fossils of animals found in various
Continental landmasters then how the South American east East
Coast kind of looked like a missing puzzle when joined with the
African West Coast so things like that were Alfred Wan's arguments
now what happens is the post- drift studies gave some valid
arguments and information against Wagner's continental drift
theory especially mapping of the ocean floor and testing of oceanic
rocks were very crucial steps that were taken by the scientists they
revealed some real facts that gave the post- drift study good
amount of weight when compared to Wagner's continental drift
theory I know things are getting a little confused using so what I'm
going to do is create a nice differentiation between both the
theories side by side so that it makes clear sense as to what is what
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and it will also serve as a quick revision so on your left hand side is
the continental drift theory given by Alfred Vagner and on your right
hand side is the post- drift studies which were done by various
scientists just to prove the point that there are reasons much more
Beyond What wagonner suggests the continental drift theory talks
about the matching of continents Wagner said if you look at South
America and Africa they look like a jigsaw puzzle fit when brought
closer which is true that once upon a time both land masses were
together but the reason behind that is much more deeper than just
merely looking at the world map and saying they were ones
together the second point in continental drift theory talks about the
fact that rocks from different continents were of the same age and
this point made Vaga believe that the land masses were once
together and they slowly drifted away again the reason behind the
drifting is much deeper than just looking at rocks and saying they
all are same the third point in continental drift theory talks about
tillite formation the Gana land consists of six land masses they are
India Africa Madagascar Australia Antarctica and folkland Islands
under the base of these six land masses teite sediments were found
so that made Vaga think that okay these six land masses were once
together and now they are aart so this is a pretty good observation
however the reason is much bigger and in depth rather than
observing Delights the fourth point in continental drift theory talks
about Placer deposits they are deposits of Rich minerals like gold
diamonds Etc so if you look at the coast of Ghana and then coast of
Brazil you'll see that these Placer deposits looks like Wayne that
were once joined together this point again made vagona believe
that Africa and South America was once a single landmar and the
last point in continental drift theory talks about distribution of fossils
when identical species of plants and animals were found on
landmasses it made Vaga strongly believe that once upon a time
there was only a single landmass and with time it started splitting
into different continents so these were the evidences of Alfred
wager that made him come up with the continental drift theory now
coming to the right hand side that is the post drift studies after the
World War II many discoveries were made which added new

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information scientists started arguing the fact that Alfred Vagner
only looked at evidences that were collected from the Continental
areas which is true if you look at the left hand side all these
evidences were taken by simply looking at the land masses so in
the post- drift studies the scientists felt hey why don't we do some
comprehensive study by mapping the ocean floor and that led to
the convectional current theory where Arthur Holmes said it is
because of the magma present in the mantle which is causing the
ocean flow to expand since the oceanic crust is thinner than the
continental crust therefore it is easy for the magma to come out
from the ocean bed and that's why the mid Oceanic ridges give a
solid proof about this Theory and the second point in post- drift
theory is the mapping of ocean floor when the ocean floor was
being mapped scientists saw that ocean bed is not a flat piece of
land it has similar terrain uneven surface just like we have on land
this was an astonishing finding and then they also went on to find
mid Oceanic ridges on the ocean bed which are these long range of
mountains that were formed due to the rocks that came out of the
mantle in the form of magma and when scientists took samples of
rock from the mid Oceanic ridges as well as from the Continental
side they found that the rocks from the mid Oceanic Ridge were
comparatively younger in age hence they concluded as we move
away from the mid Oceanic ridges the age of the Rocks increases so
this was the post- drift studies which totally focused on the concept
of sea flow spreading that is the ocean flow gets pushed to the
opposite side due to volcanic eruption at the crest and making the
sea flow spread and it was presented by Harry hes in 1961 whereas
the continental drift theory by Alfred Wagner focused on the
argument that all the continents were once upon a time a single
Continental Mass named pangi and then the single Continental
Mass began to split into smaller ones and that's how the world looks
today so if you see two totally different theories proposed by two
different people

hold on we are not done yet now we have a third concept which
brings us to the topic plate tectonics now this is the third concept
that tries to answer the questions related to distribution of oceans
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and continents if you see this entire chapter so far has been trying
to answer the questions related to distribution of ocean and
continents I mean that's what the title says and we have so far seen
two theories the concept of PL tectonics was presented by mezi
Parker and Morgan three people in 1967 just after 6 years of hess's
SE floor spreading Theory so what the plate tectonic Concepts say
is the lithosphere which is also the combination of crust and upper
manle it is in the form of irregular slab of solid rock so think of the
lithosphere as a large plate and now when a plate breaks this is
exactly what it looks like when we say irregular slab of solid rock
this is what the plate tectonics concept is suggesting so we know
that lithosphere consists of crust and upper mantle and the crust is
both continent Al as well as Oceanic in nature the oceanic crust is
thinner than Continental but in general it is one complete crust
hence the lithosphere covers both ocean as well as Land And now
when we think of a plate we can easily relate that a plate consists of
land as well as ocean doesn't matter which of the two occupy a
larger portion of the plate

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now let's look at the world map according to this New Concept
which is plate tectonics our entire Earth surface is divided into
seven major and some minor plates and the these major plates are
the first one is Antarctica and the surrounding oceanic plate and the
second one is North American with Western Atlantic flow separated
from South American Plate along the Caribbean islands plate the
third one is South American with Western Atlantic floor spread it
from the North American Plate along the Caribbean islands plate
and the fourth one is Pacific Plate and the fifth one is India Australia
New Zealand plate and the sixth one is Africa with the Eastern
Atlantic floor plate and the seventh one is uraia and the adjacent
oceanic plate

now let's look at some minor plates the first one is Cocos plate
which is between Central America and Pacific Plate then we have
nasca plate that is between South America and Pacific Plate and
then we have Arabian plate mostly the Saudi Arabian Landmark
then we have Philippine plate between Asiatic and Pacific Plate and
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then we have Caroline plate between the Philippine and Indian plate
north of new guinia and the last one is Fuji plate that is northeast of
Australia

now the reason this plate tectonic theory is so interesting is

because it makes a very important argument that continents do not
move in fact continents are part of these plates and it is the plates
that has been moving throughout the history of Earth and it will
continue to do so in the future as well I hope you're getting what I'm
trying to say so if you remember Alfred wner said that initially
everything was one single land mass named as Pang but it
according to new discoveries it is now believed that Pang existed
due to the convergent mechanism of plates on which continents
reside convergent means coming closer

now we're going to read about three types of plate boundaries

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the first one is divergent boundaries the meaning of the word
Divergent is pulling away so plates that moves apart from each
other is due to Divergent mechanism and it creates a fault or
depression which is known as divergent boundaries places where
plates move away is also known as spreading one such example is
the Mid-Atlantic Rich here the American Plate is separated from
Eurasian and African plates

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the second one is convergent boundaries now convergent is
opposite of Divergent meaning coming closer so what happens
when two plates come towards each other one plate Dives under
another and it is usually the smaller plate that converges under the
bigger plate leaving that land area a little uplifted so this
mechanism happens between an oceanic and Continental plate
then between two oceanic plates and then finally between two
continental plates

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the third one is transform boundaries in this mechanism what
happens is the motion of the plate is horizontal or in other words
here the two plates slide past one another I mean the best way to
imagine is look at this picture and see how the plates are moving
past one another now that we have read about different plate
movements it's time to understand what is the rate at which these
plates move I don't know whether you have seen this program that
used to come on Discovery called strip the city in that they
discussed in one of the episodes how geologists find the rate at
which the plates are moving it is very fascinating to see what they
do is they Place sensors all over the regions to record movs of a
plate they use an instrument called creep meter it monitors the
slow surface displacement of an active geologic fault in the earth its
objective is to record the tension that's building up in the Falls they
put two rods attached with steel wire so when the Surface starts
moving it puts the wire and the geologist measure that expanding
Gap it's usually measured in millim and roughly a fault moves
around 5 to 10 mm a year I recommend you watch that video in
your free time it's really fascinating

now come to another important topic what is it that is making these

plates move I mean what is that Force so when we see Earth we see
this round solid body floating in space right but I want you to know
this solid body is not motionless if you have seen my video on
different layers of Earth in that I have explained the mantle consists
of molten rock and how this magma moves in a circular manner
making the upper mantle a weak layer and from this weak layer
often heated material Rises to the surface spreads and then sinks
back again this cycle keeps repeating over and over to generate
what scientists call a convection cell or convective flow again you
can go back and look at the convectional current theory that we
discussed under post drift studies so to answer the question what is
the force that is moving the these plates the answer is it is the soft
mantle and the circular flow of heated material inside the earth
which is the driving force behind the plate movement

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Initially, India was part of the Australian Plate, located as a large
island off the Australian coast. This plate was once a part of
Gondwanaland, around 200 million years ago. India then broke
away from the Australian Plate and started moving northward
towards the Eurasian Plate about 40-50 million years ago. Around
50 million years ago, as India collided with Eurasia, the land
underwent rapid uplift due to the convergent mechanism, forming
the Himalayan mountain range. Before this collision, there was the
Tethys Sea and the Tibetan block between India and Eurasia. During
its movement, roughly around 60 million years ago, the Indian Plate
experienced massive volcanic eruptions, leading to the formation of
the Deccan Traps, which are made of solidified lava, confirming past
volcanic activity. The Indian Plate includes Peninsular India and the
Australian continental portions. On the northeastern side, it extends
through the Rakhine Yoma mountains of Myanmar towards the
island arc along the Java Trench, slightly subducting under the
Eurasian Plate. On the western side, it borders the Arabian Plate,
which extends up to the Red Sea, while in the south, it connects to
the Antarctica Plate through an oceanic ridge, which marks a
divergent boundary. The movement of the Indian Plate is a crucial
part of understanding the distribution of continents and oceans. In
this chapter, we discussed three major theories: the Continental
Drift Theory by Alfred Wegener, the concept of Seafloor Spreading
proposed by Harry Hess as part of post-drift studies, and the widely
accepted Plate Tectonics Theory presented by McKenzie, Parker, and
Morgan, which explains the distribution of oceans and continents.

Rock Cycle

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Now, this is a picture of the Rock Cycle. No rock remains the same over time;
due to pressure and other natural forces, they transform. Remember, we called
igneous rocks as primary rocks, and the reason is that they are directly formed
from magma and lava when these materials solidify. Anything that is formed
from the most basic component of the Earth has to be termed as primary rock.
Now that we know igneous rocks are called primary rocks, we understand that
sedimentary and metamorphic rocks are called secondary because they are
formed from igneous rocks.

Let me explain how. You see, igneous rocks are the reason sedimentary and
metamorphic rocks exist. Let's look at it as a story. Imagine magma coming out
of the mantle through a volcanic eruption. This magma cools down and
solidifies into crystals, forming igneous rocks. Over time, various weathering
agents—or exogenous forces—such as wind, rain, and glaciers act on these
igneous rocks, breaking them into small fragments or debris, which we call
sediments. These sediments are buried under layers and, with time and
pressure, compact together to form sedimentary rocks. This process is called
lithification.

Now, sedimentary rocks also have the tendency to break apart again into
smaller debris or sediments. But how are metamorphic rocks formed? Think of
a caterpillar changing into a butterfly—we call that process metamorphosis. A
similar transformation happens to rocks, especially when they are exposed to
heat between 300 to 700 degrees Celsius. But where does this heat come
from? Inside the Earth, there is a tremendous amount of heat due to pressure.
If you press your hands together very hard, you can feel the heat. Rub them,
and due to friction, you'll generate even more heat. Similarly, when Earth's
tectonic plates move and converge, they produce heat and build mountains,
creating immense pressure. This heat "bakes" rocks—just like how you bake
cookies from dough. The dough doesn’t melt, but it changes form. Similarly,
rocks do not melt but transform into metamorphic rocks.

That’s why metamorphic rocks are mostly found in mountainous regions. Again,
with exogenous forces like wind and water, metamorphic rocks can break down
into sediments, which can later form sedimentary rocks. The Rock Cycle never
stops. Metamorphic and igneous rocks also find their way back into the mantle
through subduction. This happens when two tectonic plates converge, and one
plate goes under another, carrying rocks into the mantle. Since the mantle
consists of molten rock called magma, these rocks eventually melt. Magma
then resurfaces through volcanic activity, forming new igneous rocks. This
continuous process is what we call the Rock Cycle.

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Geomorphic process

"Geo" (Earth) + "Morphic" (Shape/Form) → Study of Earth's surface formation.

Earth's surface is uneven with uplands & lowlands due to geomorphic
processes.
Two main forces shape the Earth's surface:
1. Endogenic Forces → Internal forces originating within the Earth (e.g.,
volcanic activity, earthquakes).
2. Exogenic Forces → External forces acting on the Earth's surface (e.g.,
weathering, erosion).

so now the question is what are these forces so to understand this you just have to
think first what happens inside the Earth's surface or what happens in the interior of
the earth so the Earth has different layers in this mantle which is just below the crust
is filled with molten rocks known as magma and magma is continuously moving in
circular manner this movement of magma in the mantle creates convection currents
and this is what causes the plates which includes Oceanic as well as continental crust
to move, earthquakes are also caused because of this then volcanic eruption takes
place because of this so all these are endogenic forces that arises from within

now the other force that is the exogenic forces this acts on Earth's surface from
outside for example sunlight it is constantly heating up the Earth's surface then we
have rain which is responsible for weathering of rocks then we have wind that takes
the soil from one place to another then we have ice Glacier when it melts it is again
responsible for carrying the soil from one place to another so in a nutshell we can say
the actions of exogenic forces result in wearing down and filling up the Earth's surface
now I want you to imagine this line as the surface of the Earth that is the crust when
endogenic forces hits this layer you can see the changes on outside in this case the
other side of the line similarly now when exogenic forces hits this line that changes
that you saw due to endogenic force those gets weathered down or simply reduces
down and this keeps on happening at a different rate in Pace due to this timing this
line which is the Earth's crust has this bumpy ups and downs that gives it an uneven
form and that's why our earth's surface is not even somewhere you'll find Uplands and
somewhere you'll see lowlands or depression

Soil formation there is another term given to it it is called pedogenesis

the person who studies soil is called pedologist now when we think of soil these
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are tiny degrees of particles and where do these particles come from now
that's the first question in soil formation it all starts with weathering of rocks
weathering is an exogenic force rocks get weathered due to activities of wind
glaciers rivers rain waves and currents so these are agents that help in
weathering rocks but how does it happen that's what we will see now so when
it rains water falls on the rocks and seeps into the cracks of rocks and freezes
frozen water expands and that exerts pressure on the walls of the rock this
pressure is enough to make the walls crack further apart thus expanding and
deepening the cracks this is what happens to city roads and footpaths that's
how they crack another way rocks crack is due to the actions of plants and
animals some plants like mosses and lichens are capable of growing without
soil on bare rock while growing their roots penetrate into the rocks by creating
pores and when mosses and lichens grow into grasses and ferns then it grows
into later on bushes and trees this causes rocks to split apart as the roots force
their way down through these rocks the same mechanism how water splits
rocks if you dig into the soil deep at some point you will reach the bedrock now
what animals do is they create holes in the soil by digging that allows water to
reach down to the bedrock and same thing happens again water splits the rock
this is how rocks break down and soils are formed

Landforms and Their Evolution

From the name of this chapter, we can figure out that we are going to read
about the process by which various landforms were formed. "Landform" means
land formation. The Earth's surface is an uneven terrain—somewhere you’ll find
plain land, while elsewhere you’ll see elevated features like mountains or
plateaus. In some places, you will also find deep trenches or depressions. Each
landform, or terrain, has its own physical shape, size, and material
composition. For example, mountains have rocky material inside because, as
we learned in the previous chapter, mountains are formed due to convergent
boundaries, where crustal plates move towards each other. In this process, one
plate subducts under another, causing intense compression, twists, and folds in
the rock layers, ultimately leading to the elevation of a mountain. Similarly,
plains are formed over millions of years due to the action of running water,
which erodes the surface and smoothens it into a leveled landform. Here, you
will find fewer rocks and more sediment particles. This is how every landform
has its unique shape, size, and material composition.

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In a nutshell, this chapter explains how different landforms came into
existence. Every landform has a beginning. This statement is true because, as
we have studied in the chapter on geomorphic processes, all landforms are
created due to endogenic forces—forces that originate from within the Earth's
interior. However, once a landform is formed, it does not remain unchanged.
Over time, it may undergo changes in shape, size, and nature, sometimes
slowly and sometimes rapidly, due to the continuous action of geomorphic
processes and external agents. These changes occur due to exogenic forces,
which are generated by atmospheric and solar influences. The combined effect
of endogenic and exogenic forces leads to the continuous modification of
landforms. However, these changes do not occur instantly; they take place in
stages over a long period—sometimes millions of years. Through these slow
but constant transformations, landforms evolve from one form to another. This
gradual process of transformation is what we refer to as evolution, which
means the stages of change that landforms undergo after their formation.

Now these changes in the landform that we spoke about they happen due to
two reasons erosion and deposition erosion means varying down or destruction
and deposition means piling up or construction so rain wind glacier sea wave
all these are called exogenic agents and they are the reason behind erosion
and deposition of landforms they create as well as break down a land form
these are called geomorphic agents and they act over long periods of time and
produces systemic changes leading to sequential development of landforms
hence we can also say that erosion and deposition are the two important
aspects in the evolution of landforms now here it says most of the geomorphic
processes are imperceptible now the meaning of the word imperceptible is
undetectable and observable in other words something that is very hard to
observe because nature has a very slow movement of development I mean
when you look at a landscape it's very rare that you can say I have a before-
and-after picture of this landscape I'm not saying it's not possible many people
have taken such pictures where you can see a landscape being totally changed
in few years but generally it's very rare and it is because of the fact that this
process is imperceptible it takes usually thousands of years to see a noticeable
change of a comparatively bigger landscape now why is this process
imperceptible or in other words why is it slow the evolution of landforms is a
slow and long process and what makes it slow and long has both dependent as
well as independent reasons behind it we know that exogenic forces acts as
very heavily on these natural structures especially structures in the form of
folds Falls joints and fractures the exogenic forces changes them to a lot extent
for example in a fold structure the exogenic agents makes it steeper on the
sideways forming an intense sharp slope in a false structure the exogenic
agents can make default into a narrow Valley so you see the changes in the

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land form is directly dependent on the exogenic factors and this entire process
is imperceptible meaning it takes a lot of time to see a noticeable change and
then there are independent factors now these are something that we read
about and probably cannot see it and that's what makes it an independent
factor so there are three controlling factors that independently influence the
evolution of landforms I want you to remember this because once you
understand these factors you'll be able to make your own analysis on many
other geography related topics now these three factors are the first one is
stability of sea-level.

Now I'll tell you how sea-level affects landforms sea level changes due to
increase or decrease in the volume of water in the ocean now how does the
volume of water in the ocean increases it happens when glaciers or large sheet
of ice melts because of increasing temperature so when glaciers melt the water
stored in that glacier enters the hydrological cycle meaning the ocean water
will get more water its volume will increase now imagine if you have a tub and
you will fill it up with water and then you keep adding more and more water
you'll notice that the wall of the tub will expand it may also break at some point
but for argument's sake let's just stick to expansion similarly the increase in
ocean water will exert pressure on the continental shells and not to forget
oceans have currents that will increase the horizontal push from time to time
so there will be some minor changes in the continental landforms because of
the sea level the second one is tectonic stability of land masses we have read
about the theory of plate tectonics in previous chapters and it is a universally
accepted theory when it comes to the evolution of continents and oceans we
know that the continental and oceanic plates are divided in the form of some
major and minor plates and it's the movement of these plates that give rise to
mountains and Falls and it is also the same reason why earthquake occurs so
tectonic stability of land masses is an influential factor in the evolution of
landforms the third one is climate now Mountain plateaus and other types of
topography are formed due to energetic forces meaning the forces that are
generated from within the Earth's interiors now once they are formed they go
through intense chemical and physical weathering due to exogenic forces like
sun rain wind glacier waves etc now all these are dependent on climatic
condition and we also know that climate is not same everywhere temperature
drops as we go away from the equator with differences in temperature earth
material goes through intense chemical as well as physical changes rocks
break down due to constant heating and cooling condition then bacteria like
mosses and lichens causes chemical reaction and even that breaks down the
rock and this is all possible due to climate and that's how climate influences the
evolution of land form so this is how these three independent controlling

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factors can upset the systemic and sequential stages in the development of
evolution of landforms

Now we are going to read about some exogenic agents that reduce land
masses through erosion and at the same time it also helps in developing new
land forms the first exogenic agent is running water you know the meaning of
running water now there are two components to it the first component is
Overland flow which basically is an excess water that is generated due to
heavy rain storms flood melting or any other sources that close over the Earth's
surface in other words when the amount of water accumulating on the land
surface exceeds the infiltration capacity of the soil so basically soil is porous
and it sucks water right there will be a point after which it can no more take in
any water then the water starts overflowing so that is known as Overland flow
the second component of running water is linear flow which is basically it
reverse streams that just flow naturally in a straight linear fashion on its own
course paths so running water is considered the most important geomorphic
agent when it comes to degradation of land now I will explain how running
water is such a powerful agent now we know that running water causes erosion
meaning it carries the soil from one place to another and not to forget the land
surface has to be a little steeper or we call it as gradient it has only den the
water will flow so there has to be an upland now the higher this land surfaces
the water flow is going to be faster standard physics so this is the infrastructure
part now if the velocity or the speed of these running water is fast and vigorous
due to the height of the land surface because higher the land the faster the
flow this phenomena will cause erosion massive mud and rock debris will be
removed from one place to another in this case all the mud and rock de breeze
will go downwards and starts depositing in this low land area now with time the
soil layers is then automatically the speed of the river decreases so instead of
flowing in linear path it starts flowing literal meaning sideways and then the
process repeats water then finds a depression or a lowland and starts to float
there and with it carries the soil we call it little erosion of riverbanks and this
way slowly the entire valley is converted into plains hence when we see this
question here is complete reduction of relief of a high land mass possible the
answer is yes it is possible as just explain the process but the important point
to note is that this geological change will take a long period of time even a
lifetime would be less.

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Now movements back we read about Overland flow it is also called as surface
runoff let me repeat it again in this axis water due to heavy rain storm sludge
melting of ice or other sources flows over the Earth's surface basically overflow
of water occurs on Earth's surface this is what is called Overland flow now
when Overland flow occurs it causes sheet erosion by sheet we mean a
complete layer of soil which is like a sheet it gets washed away now why does
it wash away because of the velocity or speed of the running water now one
thing to understand over here is that Earth's surface is irregular meaning it's
not smooth because of this is regularity of the Earth's surface the water flow
will take either an arrow or a white part and then water flows in this narrow and
white parts due to the friction of the flowing water many minor or major
quantities of material Earth's material from the surface of the land are removed
in the direction of flow and then earth material like mud and rock has removed

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small and narrow rails will form rails are these designed that you see on the soil
then moving forward these wills will gradually develop into long and wide
galleys I guess we all know what gullies are the gullies will further deepen
widen lengthen and unite to give rise to a network of valleys I know it must be
a little difficult for many of you to comprehend as to what I said and showed in
a very short and quick way I'll illustrate what this various stages of landscape
looks like when they face running water so in the beginning the rivers ideally
starts from an elevated land portion and go straight in linear fashion if we look
at it from side view the river flows in between v-shaped valleys you must have
seen those pictures where rivers flow in between mountains this is called as
youth stage as time goes by enough soil gets deposited and the speed of the
river slows down so instead of flowing in a straight linear manner the river now
begins to meander side to side and it enlarges it's part that is live River Park
this is also known as little erosion and this is called the Metro stage again with
time due to lateral erosion River enlarges the size of the valley so much that
you can't really tell it's a valley anymore so much meandering takes place that
the river eventually converts the valley into penny plain and if you notice
during meandering in-between you will find isolated blocks of rocks which are
known as monad NOK this is the old stage of landscape evolution due to
running water now the entire cycle can stop here but if the river finds
depression or a lowland then the cycle would repeat again and form valleys or
in simple terms the youth stage would repeat again so I hope with this
illustration you are now familiar with different stages of landscape which
happens all the curse of running water.

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Original landforms are those created by erosion. One such landform is a valley.
Valleys start as small and narrow rills, which gradually develop into long and
wide gullies. These gullies further deepen, widen, and lengthen to give rise to
valleys. There are different types of valleys depending on their shape and
dimensions, such as V-shaped valleys, gorges, and canyons. A V-shaped valley
has a distinct "V" pattern. A gorge is a deep valley with very steep and straight
sides, making it narrower than a V-shaped valley, with cliffs on both sides. A
canyon, on the other hand, has steep step-like side slopes and is as deep as a
gorge. The key difference between a gorge and a canyon is that a gorge has
equal width at its top and bottom, whereas a canyon has a wider top compared
to its bottom.

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Page 35 of 107
The second type of original landform is plunge pools and potholes. Let me first
tell you what potholes are. It is similar to the pothole that you see on roads, but
in a riverbed, the scenario is different. When flowing water encounters bedload,
a bedload is a heavy sediment particle that does not move. Because of this, the
flow of the water is diverted, and the diverted flow of water forms something
called eddy currents, which is a down-cutting current, and this current causes a
depression in the riverbed. These depressions deepen, and pebbles and
boulders can get trapped in them. As a result of the eddy currents, the pebbles
drill into the depression, making them more circular, wider, and deeper. Now I
will tell you about plunge pools. When water flows over the waterfall, it creates
a plunge pool at its base due to the force of the falling water. It creates a
depression at the base. This phenomenon is called a plunge pool. Basically,
plunge pools are formed by the natural force of falling water.

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The third type of original landform is incised or entrenched meanders. The
meaning of the word "incised" is cut or cutting. You must have heard this word
in "incisor teeth," the front four teeth we have for biting and cutting food. Have
a look at this picture: in this, the river or stream is as usual flowing in between
the landscape. We can call this landscape a canyon—do not mistake it as a
gorge. You see the side cutting on the landscape? This cutting is called
"incised," and a meander is the irregular turn of the river. So, incised meanders
are meanders where the base level of the river has fallen to such an extent
that the vertical erosion is so powerful that it starts down-cutting the
landscape, just like how I showed you in the picture. Now, let's answer this
question: What are the differences between incised meanders and meanders
over flood and delta plains? In an incised meander, vertical erosion of the
landscape is very powerful due to the gradient or elevation of the landscape.
On the other hand, in the delta plains, which is a plain land, lateral erosion—
that is, sideways erosion—is more powerful. In plain or delta areas, you will not
see much landscape cutting; instead, you will see tributaries of the river
flowing laterally. But in an incised meander, the river will go vertically long and
erode the landscape to such an extent that you will start noticing cuts on the
sides of the landscape.

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The fourth type of original landform is river terraces. We’ve heard the word
"terrace" from the term "terrace farming," in which many steps are developed
to reduce soil erosion. Similarly, in river terraces, the landscape looks like
steps. These surface steps act as markings that represent old valley floors or
floodplain levels. Terraces are formed due to vertical erosion, meaning the flow
of the river is so strong that it erodes the surface vertically. These terraces can
be of different heights depending on the irregularity of the landform, or they
can be of the same height, which is called paired terraces. If the flow of the
river is not uniform, it develops into unpaired terraces. Several factors

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contribute to the formation of unpaired terraces.

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The first reason is receding water after peak flow. When a large volume of
water flows and then suddenly decreases, the river channel narrows, leading to
the formation of narrow gullies, which result in terrace formation.

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The second reason is a change in the hydrological regime due to climate
changes. Climate change often raises concerns about increasing ocean water
levels, which can cause flooding, leading to unpaired terraces.

The third reason is tectonic uplift. When a portion of the Earth's surface is
uplifted due to tectonic activity, it significantly alters the river’s flow,
contributing to unpaired terrace formation.

The fourth reason is sea level changes, particularly for rivers close to the sea.
When the sea level rises, excess water flows into the land through rivers,
causing floods and ultimately leading to unpaired terrace formation. With this,
we have now covered the four types of original landforms that exist due to
running water.

Deposition in landforms occurs due to the accumulation of soil sediments.

Deposition happens when rocks are eroded by exogenic agents like wind, air,
water, and glaciers, breaking them into smaller sediments. These sediments
are then transported by the same exogenic agents and eventually deposited in

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another place, leading to the formation of depositional landforms.

The first type of depositional landform is alluvial fans. Alluvial fans are formed
when streams flowing from higher elevations break into foot slope plains of low
gradient, taking the shape of a cone. They usually occur in mountain slopes or
elevated areas, where the speed of running water allows sediments to be

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deposited in the foothill areas. Many such alluvial fans can be found in the
foothills of the Himalayan range, where glacial meltwater from the mountains
turns into river streams, depositing sediments and forming alluvial fans.

The second depositional landform is deltas. A delta is a landform created by the

deposition of sediment carried by a river as it enters slower-moving or standing
water. This process occurs when a river flows into an ocean, sea, lake,
reservoir, or another river with a comparatively slower movement. Due to the
stillness or reduced speed of the water, the sediments begin to accumulate,
gradually forming deltas.

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The third type of depositional landforms is floodplains, natural levees, and point
bars. Now, what is the meaning of the word floodplain? An area or a plain land
that is subjected to flooding. This area is especially a low-lying area adjacent to
a river. So we are talking about this portion over here, and floodplains consist
of sediments that are transported by a river. So just as erosion makes valleys,
deposition develops a floodplain.

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Page 45 of 107
Always remember, a river initially flows from a gentle slope area, meaning it
needs a little gradient for that natural push. If the speed or velocity of the river
is high, then it will transport large-sized materials like big rocks and boulders
and massive chunks of mud, and this is what forms the riverbed. As the speed
or velocity of the river slows down, fine-sized materials like sand, silt, and clay
are carried. That’s why in hilly areas, these riverbeds consist of big rocks and
boulders because of the heavy flowing of the river, and in plain areas where the
speed is comparatively slow, you will find soft sand on the riverbed. So
wherever you see soft silt and sand touch the floodplain, a riverbed is an active
floodplain, and the area near the riverbed is called an inactive floodplain.

This region consists of two types of deposits: flood deposits and channel
deposits. In plain areas, the river flows laterally, and they often change course.
That’s why they are called river meanders, and the meanders get filled up
gradually with sediments, and this is called channel deposits. Sludge deposits
are formed when a riverbed overflows and water in it spills above the bed.
Because of this overspill, the water then takes the sediment to the side of the

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riverbed, and that is what is called flood deposits.

Now, natural levees and point bars are also associated with floodplains. You see
this picture—this is what natural levees are. Natural levees are found along the
banks of large rivers. They are low, linear, and parallel ridges. During flooding,
as the water spills over the bank, the velocity of the water comes down, and
large-sized and high-specific gravity materials get dumped in the immediate
vicinity of the banks as ridges. They are high near the bank and slope gently
away from the river. Always remember, the meaning of the word ridge is a
long, narrow land that is uplifted, and here it happens because of deposition.

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Now, it’s point bars. Point bars are also known as meander bars. They are a
depositional feature made of alluvium that accumulates on the inside bend of
streams and rivers. Look at this diagram—when a river or a stream flows, it
forms meanders. The highest energy is near the outer edge of the riverbank.
The stream energy is much lower on the opposite side, that is, the inner side.
Here, it cannot carry as many sediments and becomes depositional. This is how
it goes on to form point bars. They are almost uniform in profile and width and
contain mixed sizes of sediments.

The fourth type of depositional landform is meanders. A meander is the flow of

a river in zigzag, curly turns—basically, it's a curve in a river. The position of
the curves changes over time. The river erodes sediments on the outside of the
curves and deposits them on the inside of the curves. If you see, a meander is

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not a landform but is only a type of channel pattern.

Think about this: when a river flows from a great height, because of the height,
the speed of the water is high, and the flow is usually straight. The moment the
height decreases, the speed of the water becomes extremely slow. Water then
flows leisurely and starts working laterally, sideways. Since the surface of the
Earth is irregular, the riverbank slowly transforms into a small curvature. In the
inner area of the curve, deposition of sediments takes place, and on the
outside, erosion occurs. If there were no deposition or erosion, then there
would be no meanders. As meanders grow into deep loops, the river eventually
takes a shortcut, and the leftover curve is called an oxbow lake.

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The fifth type of depositional landform is braided channels. Now, girls have this
hairstyle called braided hairstyles—it totally resembles how a braided channel
flows. This is what a braided channel looks like: when a straight-flowing river
diverts its flow, a little erosion takes place. Due to that, sediments get
deposited, forming tiny islands. These tiny, temporary islands create a number
of water channels, which form a braided pattern. So basically, the water flow is
divided into multiple threads. These thread-like streams of water rejoin and
subdivide repeatedly, giving a typical braided pattern. So these were the five
types of depositional landforms that exist due to running water.

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Climatology
ENSO
If you break it, ENSO stands for El Niño and Southern Oscillation because the
ENSO phenomenon mostly occurs in the Southern Hemisphere, just right below
the equator. When you look at the term oscillation, it gives us a hint that
something oscillates from one place to another or back and forth. Well, it's the
temperature that we are talking about, and not just any temperature, but
ocean temperature. It is the ocean temperature that oscillates back and forth
from warm temperature to cool temperature and vice-versa.

W E

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You see, the Pacific Ocean is this large pool of water that exists on the western
side of the American continent and the eastern side of the Asian and Australian
continents. This large pool of water gets intensely warm due to the fact that it
exists right at the equator, and we all know that the equatorial region receives
a great amount of sun rays all throughout the year.

To understand how ENSO occurs, we will need to break it into three phases.

The first phase is the neutral phase. Actually, there is no such thing as a
neutral phase when it comes to any of nature's phenomena. You see, nature
has a constant, ongoing cycle that has never stopped. But for our own
understanding, we will have to create a neutral state where we can see how a
particular thing starts and goes on. So, the first phase among the three phases
is the neutral phase. In this phase, the Central Pacific Ocean is warm.

Now, let's bring in the trade winds. Trade winds are these winds that blow in
the tropical region from the eastern side to the western side. They are also
known as tropical easterlies. So, as we know that the equator receives a great
amount of sun rays, that’s what warms the Pacific Ocean. The trade winds push
the warm ocean current towards the Asian side because trade winds blow from
east to west, and that makes the western Pacific Ocean warm. You know the
region around New Zealand, Australia, and Indonesia—this region is called the
western Pacific pool. Here, the ocean temperature is warm.

The warm ocean current affects the surrounding atmosphere by increasing the
temperature as well as the moisture content, and we know that warm air rises
high into the atmosphere. It is through the convection process, and that's how
clouds are formed, and then it rains. The warm air then travels east towards
the eastern Pacific Ocean. You know, the region near South America, especially
countries like Ecuador and Peru. The warmer air, when it goes up, reaches the
end of the troposphere, and if you know, the top of the troposphere is cold.
When warm air meets cool air, slowly it loses its moisture content, and the air
becomes dry. The dry air travels towards the eastern Pacific side and comes
down over the Peruvian coastal region, making the region cold.

This pattern of rising air in the west and falling in the east continues, and it is
known as Walker circulation. So, this was the neutral phase.

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Now comes the second phase—it’s called El Niño. So, in the neutral phase, we
saw that the trade winds played an important role in pushing the warm ocean
current towards the western Pacific. Now, in this phase, the trade winds are
weak. Yes, there are a few months in a year when the trade winds are weak.
When the trade winds are weak, the warm ocean currents do not get any kind
of push. So, what happens is the warm pool of ocean water at the western
Pacific slowly moves towards the central and eastern sides of the Pacific Ocean.

So, this is where the oscillation term comes in. You see, the warm ocean current
is replacing the cold ocean current that exists in the central and eastern Pacific.
When I say replace, what I mean is that the cold water is dense, and it settles
down in the deep ocean, and warm water goes up and takes over the surface of
the ocean. When this warm ocean current moves, everything that is associated
with it—like the convection process, the formation of rain clouds—everything
moves along with this warm ocean current.

What you will notice now is that the Walker circulation that we saw in the
neutral phase, that one big looping pattern, is now breaking into two parts. Just
look at this loop. As a result, the ocean temperature near Australia is cool, and
there is no rain. The inland parts of Australia witness severe drought
conditions. But on the other hand, near the Peruvian coast, the warm pool of
ocean current brings heavy rain and floods to the American continent. So,
whenever you hear the word El Niño, immediately think of warm ocean current.

And the third phase is La Niña. This is similar to the neutral phase. In this
phase, the trade winds are strong. Since trade winds blow from east to west,
they push the warm ocean current from the eastern Pacific toward the western
Pacific. Now, imagine this—cold water is dense, and it settles down in the deep
ocean, so that means the temperature of the ocean surface is warm. Now, if
the trade wind pushes the warm surface ocean current towards the western
Pacific, the cold water from the deep ocean immediately comes up to the
surface. There’s a word given to it—it’s called thermocline. Thermocline is the
rising path of water temperature, and the rest of the process is the same.

We saw that in the neutral phase, the western Pacific region of Australia,
Indonesia, and New Zealand gets heavy rains. The effect of La Niña is stronger
on these countries than El Niño. So, El Niño is a warm ocean current, and La
Niña is a cold ocean current. If El Niño is at the eastern Pacific, then La Niña will
be at the opposite region, that is, the western Pacific, and it oscillates back and
forth.

Easterlies, Westerlies, Subtropical highs, and

Subpolar lows.
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Atmospheric circulation and its patterns
Now, there are these two months in a year that you need to specifically
remember: January and July. During the month of January, the Northern
Hemisphere has the ongoing winter season, and I think you can easily figure
that out because, in the months of December and January, it's winter and chilly.
Now, what that means is the Northern Hemisphere of Earth is tilted away from
the Sun, and that makes the Southern Hemisphere exposed more towards the
sun rays. Likewise, in the month of July, the Northern Hemisphere witnesses the
summer season. This time, the Southern Hemisphere of the Earth is tilted away
from the Sun, making the Northern Hemisphere exposed more towards the sun
rays. Now, whether it is January or July, one thing you must keep in mind is that
near the equator, the sea-level pressure is always low, and the area is known
as the equatorial low. The reason behind that is, however the Earth moves or
rotates, the equator receives insolation all throughout the year, making the
equatorial region warm throughout the year. Warm temperature makes the
surrounding air normal, and as we know, warm air rises, leading to a low-
pressure zone

let's move from the equatorial region to 30 degrees north and 30 degrees
south. These two regions are called the subtropical region. It’s a tiny little place
between the tropical and temperate zones. This region has a lot of high-
pressure areas, and that's why it is known as the subtropical highs. Now, let me
explain why this region is called the subtropical high. The reason behind that is
the Hadley Cell. To understand the Hadley Cell, you will have to look at this
illustration. The Sun is the ultimate source of energy that drives the Earth's
weather. Now, this fact should be absolutely clear to you. Most of the energy of
the Sun reaches the equatorial region, and the least energy reaches the poles.
I’m talking about the North and South Poles. Now, if there is a lot of insolation
at the equatorial region, then obviously, it will make that place warm. Similarly,
the North and South Poles are cold because a minimum amount of solar energy
reaches there. If I have to say this concept in some other way, then just
remember this: as we go away from the equator towards the poles,
temperature drops. Now, let's try to understand the atmospheric circulation
pattern because this is what redistributes heat on Earth and makes life
possible. Alright, so moments back, I told you that however the Earth moves or
rotates, the equator receives insolation all throughout the year, making the
equatorial region warm. We also know that warm air expands and rises. Now,
having said that, the warm air at the equatorial region rises and moves towards
the poles. That’s why you will find clouds and rain in the tropical region, and
you will also find that the tropical region is moist. Now, the air rising near the
equator goes up to a height of 10 to 15 kilometers above the surface and starts

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moving towards the poles. While going on its way to the poles, it comes down
or sinks at the subtropical region. This pattern of atmospheric circulation is
called the Hadley Cell. It is named after George Hadley, a famous meteorologist
who proposed this mechanism. Anyways, as the air moves towards the
subtropics, it comes down over the oceans, creating a high-pressure zone. In
the Northern Hemisphere, these high-pressure systems are located over the
North Pacific and North Atlantic Oceans. The famous Bermuda Triangle is also
located in the North Atlantic Ocean, and that’s a high-pressure zone. So, if
anyone asks you the secret of the Bermuda Triangle, this is the possible logical
reason. The air that moves from the equator towards the subtropical region is
warm. Additionally, there is cold air flowing towards the low latitudes from the
poles. As I said, atmospheric circulation redistributes heat, meaning cold and
warm air keeps moving here and there.

When cold air from the poles arrives toward the low latitude and warm air from
the equatorial

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region moves toward the poles, what do you think will happen? Cold and warm
air will collide at mid-latitudes, which is the subtropical region. Always
remember this point: when warm air meets cool air, turbulence occurs. It’s a
highly unstable situation for pilots and the aviation industry. The air will
converge, meaning it will sink. Now, I want you to think for a while. When the
warm air moves up at the equatorial region, it reaches the end of the
troposphere. At the end of the troposphere, you will find a thin layer of cool air.
Always remember, air is warm at the bottom of the troposphere, near the
ground level, and as the altitude increases, it gets colder. So, this warm air has
to deal with the cool layer of the troposphere and the cool air from the poles.
You see, it’s a two-on-one situation, making it all the more easier for the warm
air to sink over the subtropical region and become a subtropical high because
converging means sinking, and that’s what creates a high-pressure belt.
Anyways, just keep in mind, warm air and cool air collide and sink in this
subtropical region, giving rise to the subtropical high. Another important point
to remember is that when air sinks and comes down closer to the surface, it
again gets divided into two parts: one part of the wind heads back to the
equator, and the other goes toward the pole. Just keep this in mind; I’ll get
back to this in a while. Now, let's go beyond the subtropical high. In between
50 to 70 degrees in the Northern Hemisphere and 50 to 70 degrees in the
Southern Hemisphere, this region also lies at the border of the temperate and
frigid zones and is a low-pressure belt. That’s why it is known as the subpolar
low. Now, think for a while. All this time, we read that low pressure is supposed
to develop due to warm air. If you look at the equator, that region is warm, and
warm air rises, creating a low-pressure belt near the equator. But over here, it
is supposed to be cold. I mean, from the temperate zone, it starts getting
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colder. So, how is it that this region is called the subpolar low? It sounds a little
confusing, right? The straightforward logic of temperature and its relation to
pressure doesn’t seem to apply well over here, right? So, what do you think
would be the reason? Now, let's go step by step and try to understand the
logic. The first thing that we are clear about is that the low pressure in this
region is not caused by temperature. The second thing you need to understand
is that the low-pressure belt is mainly found above the oceans because the
landmass, as we know, is cold or, in some places, covered with snow and ice.
Now, if you remember, moments back, we were talking about subtropical highs.
We learned that it’s a high-pressure zone, and we also saw how it becomes a
high-pressure zone. The warm air from the equatorial region rises and moves
towards the subtropical region, where it collides with the cold air coming from
the poles, making the air sink over the Atlantic and Pacific Oceans, thus
creating a high-pressure belt. Now, if you remember, I told you that the air that
sinks at the subtropical region, forming the subtropical high, gets divided into
two parts. One part goes towards the equatorial region, and the other part goes
towards the poles. The same thing that happened in the subtropical region
happens here as well. The part of the wind that goes towards the poles collides
with the wind coming from the poles, but the wind collides nearer to the
surface. These are cool, dry winds. When they collide and converge near the
surface, they don't have any place to sink, so they rise. When air rises, it is
associated with clouds and precipitation. You see, it's creating a similar
condition that exists in the skies of the equatorial region. That's how it creates
a low-pressure zone, which is called a sub polar Low. Over here, the name of
the atmospheric circulation pattern is called the Ferrel Cell. Again, the air that
rises at the subpolar low gets divided into two parts—one goes towards the
poles, like the extreme part of the poles, and the other goes towards the
subtropics. That's how a chain or a loop is created where the air keeps moving
from the equator to the poles and vice versa. Always remember, the equator
has a low-pressure zone, the subtropical region has a high-pressure zone, then
comes the Sub polar region with a low-pressure zone, and finally, the poles
have a high-pressure zone. All these pressure positions keep changing with the
movement of Earth on its axis because that's what affects the Sun's heating of
the surface. For example, during January, when the Northern Hemisphere is
tilted away from the Sun, that's when the Northern Hemisphere has a winter
season, and the Hadley Cell moves towards the lower latitude of the Northern
Hemisphere. Likewise, in the month of June or July, it is somewhere in the
Northern Hemisphere, and the Hadley Cell shifts to higher latitudes of the
Northern Hemisphere. So with this, I hope you understood atmospheric
circulation and its patterns. Now, let's quickly understand what these westerlies
and easterlies are. Before I begin explaining that, you need to understand that
the Coriolis force affects the velocity and direction of the wind to a great

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extent. So all that we have read till now—the creation of low-pressure and high-
pressure zones—is all due to the movement of air from one place to another.
Basically, atmospheric circulation is the large-scale movement of air, which
redistributes heat energy on the surface of the Earth. So, what is the Coriolis
force? We know that Earth spins on its own axis—that's how we witness day
and night every day. The Sun rises in the east and sets in the west, which
means the Earth is spinning on its axis from west to east. Since Earth is a
sphere and wider at the equator, the rotational velocity of Earth at the equator
is more than what it is at higher latitudes. For example, at 30 degrees north
and south, the rotational velocity is less than what it is at 0 degrees equator.
Due to the rotational velocity of the Earth, winds get deflected. Now, an easy
example to understand the concern—you must have taken a ride on a revolving
circular platform in a playground or some amusement park. Now, if two people
sitting on opposite ends of this ride throw a ball at each other, you'll notice that
the ball will change its direction. With this demonstration, you can easily
understand how wind on Earth gets deflected due to the rotational velocity of
the Earth, and this phenomenon is known as the Coriolis Effect. Now, coming to
westerlies—if a moving object is going towards the north or south from the
equator, it will deflect towards the east due to the Coriolis force. So, westerlies
are prevailing winds that blow from west to east between thirty to sixty
degrees north and south. Similarly, if a moving object is going from the north or
south towards the equator, it will deflect towards the west, again due to the
Coriolis force. So, easterlies are prevailing winds that blow from east to west in
polar and tropical regions.

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composition of the atmosphere
The composition of the atmosphere refers to the different gases that make
up Earth's atmospheric layers. The three major constituents of the atmosphere
are Nitrogen (N₂), Oxygen (O₂), and Argon (Ar), which can be remembered
using the acronym NOA. These gases exist in different proportions, with
Nitrogen being the most abundant, followed by Oxygen and Argon in smaller

amounts.

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Apart from these primary gases, the atmosphere also contains carbon dioxide
(CO₂) and water vapor (H₂O), but they are found only up to 90 kilometers
from the Earth's surface. This means that these gases exist until the initial
boundary of the thermosphere, which is the fourth layer of the atmosphere.

The atmosphere is divided into five layers:

1. Troposphere – Extends up to 10 km and is the closest layer to Earth's

surface.
2. Stratosphere – Lies above the troposphere.
3. Mesosphere – Comes next, followed by...
4. Thermosphere – Where carbon dioxide and water vapor reach their upper
limit of 90 km.
5. Exosphere – The outermost layer, merging into space.
This structured composition of the atmosphere plays a crucial role in sustaining
life by regulating temperature, filtering harmful radiation, and enabling
essential weather phenomena.

Gaseous carbon dioxide is an important gas. It is transparent for the incoming

sunrays but opaque to the outgoing terrestrial radiation. Now, you must be
aware of the phenomenon that the differential heating of land and water is the
reason behind rainfall and precipitation. Having said that, we now clearly know
that Earth's surface gets heated up due to sun rays, and because Earth's
surface heats up due to the incoming sun rays, that heat has to go somewhere.
It is because of carbon dioxide that the heat is trapped within the Earth's
atmosphere. This is what is causing climate change. Now, you must have heard
about greenhouse gases; they are methane, nitrous oxide, sulfur dioxide,
ozone, and carbon dioxide. These are a bunch of gases in the atmosphere that
block the Earth's radiation from going out into space. These greenhouse gases
trap the heat within the Earth's atmosphere and make the Earth warmer. Now,
the interesting part to note is that the volume of other gases is constant, but
the volume of carbon dioxide has been rising in the past few decades, mainly
because of the burning of fossil fuels. Since the Industrial Revolution, that is,
from the mid-18th century, the amount of carbon dioxide has increased.
Machines on a daily basis are using fossil fuels like diesel and petrol, which
emit more and more carbon into the atmosphere, increasing the overall carbon

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content. Now, ozone is another important component of the atmosphere that is
found between 10 and 50 kilometers above the Earth's surface. Basically, it's
located in the stratosphere. What the ozone layer does is act as a filter and
absorb the ultraviolet rays that come from the Sun. UV rays are very harmful if
taken in excess; they can cause sunburn, skin cancer, etc. In a nutshell, they
are harmful rays. The ozone layer is protecting us from UV rays by filtering
them, but this layer is depleting purely due to man-made activities. Ozone
layer depletion is one of the most serious problems faced by our planet Earth.

Water vapor is the amount of moisture present in the atmosphere. When we

think of water, it is in a liquid state, but with vapor, it becomes a gas. Water
vapor, therefore, refers to water in both its liquid and gaseous states. The
amount of water vapor present in the atmosphere is called humidity. In India,
coastal areas are more humid because the sea in front of them releases a lot of
water vapor into the air. However, humidity is not uniform across the Earth.
Water vapor decreases from the equator toward the poles. The equatorial
region is known for its warm and wet climate because it receives direct
sunlight, leading to high evaporation, which increases water vapor levels in the
atmosphere. In contrast, polar regions have little to no moisture, resulting in
dry air. This is why cold regions cause dry skin and cracked lips due to a lack of
humidity.

Water vapor plays a crucial role in regulating Earth's temperature. It absorbs

parts of the sun’s rays, preventing the surface from becoming excessively
warm. At the same time, it also blocks some heat from escaping into space,
ensuring that the planet does not become too cold. This balance helps maintain
a stable temperature suitable for life, much like a blanket that keeps the Earth
neither too hot nor too cold. Water vapor also contributes to the stability and
instability of the air. The amount of water vapor in the atmosphere is directly
related to temperature—higher temperatures lead to more water vapor, while
lower temperatures reduce it.

If the Earth's temperature were to increase—whether due to natural causes or

the rise in carbon dioxide from burning fossil fuels—more water would
evaporate from the oceans, increasing the amount of water vapor in the
atmosphere. More water vapor leads to higher humidity, making the air feel
warmer. In humid regions, warm air rises and eventually meets cooler air. When
warm air comes into contact with cool air, it causes turbulence, leading to
rainfall and precipitation. This cycle illustrates how water vapor contributes to
both the stability and instability of the atmosphere.

So far, we saw that the tons of water vapor in the atmosphere but I want you to
know that atmosphere has a sufficient capacity to keep small solid particles.

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Now what are these particles these are dust particles that originated from sea
salts fine soil smoke from incomplete burning ash pollen dust and disintegrated
particles of meteors since dust particles are fairly heavier than water vapor
therefore they are generally found in the lower layer of the atmosphere which
are troposphere and stratosphere now it is the air movement that takes these
dust particles to create a height and a longer distance now I want you to
remember this point the higher concentration of those particles is found in
subtropical and temperate regions due to dry winds I'll show you sub tropical
and temperate regions on this world map so here the veins are try remember
moments back we read that water vapor decreases as we go away from the
equator towards the poles that means at equatorial region the moisture
content in the atmosphere does not allow the particles to rise but then as we
go away from the equatorial region moisture content in the atmosphere
decreases and drivin carries the dust particles and as we go further away at
poles area I'm talking about North Pole and South Pole there you will hardly find
any dust particle you will mostly see ice crystals I don't know if that can be
called as dust particle another important point is that dust particles are a major
component behind cloud formation now if you see there is water around us all
the time in the form of tiny gas particles which is also known as water vapor
then there are also tiny dust particles floating around in the air now if you look
closely at a black background you can see the dust particles so the
combination of this water vapor and dust particles together form the cloud
obviously you must have heard that cloud is a result of condensation where the
water vapor turns into visible water droplets but then if there isn't anything to
hold them up in the air how will a cloud form otherwise droplets will fall and it
will simply drain so to hold this condensed water droplet floating dust particles
come into picture these are called aerosols these aerosols attract the
condensed water droplets and large combination of these forms a cloud so

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that's the role of dust particles.

Now let's get to know quickly about different layers of the atmosphere. So this
is the picture of different layers of the atmosphere from the lowermost layer to
the outermost layer. Overall, there are five layers—remember this order. Now
these layers have different density and temperature. Density is highest near
the surface of the Earth because of the gravitational pull of the Earth, and as
we go higher, the density decreases. Now coming to the temperature part, the
lowest layer, that is the troposphere, is hotter because it's nearer to the Earth's
surface, so heat from the Earth warms up the air of this layer. As the height
increases, the number of air molecules decreases, and that certain pressure
decreases, and this continues till the end of the mesosphere. Now this place is
also called the mesopause. This is the coldest part of Earth's atmosphere,
where temperature falls up to minus 90 degrees Celsius. Now after the
mesosphere, we have the thermosphere. By the word "thermo," you can relate
it to the word "thermal," which means heat. Here, the temperature goes up to
500 to 2,000 degrees Celsius. Now after this, we have the exosphere. It is also
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the first layer to come into contact with and protect the Earth from meteors,
asteroids, and comets. Basically, after this layer, space starts. The temperature
here varies from zero to over 1,700 degrees Celsius, meaning it is colder at
night and much hotter during the day. I also remember watching some NASA
astronauts’ interviews where one astronaut said that when they go on a
spacewalk, the spacesuit they are wearing is like a mini spaceship that protects
them from the heat of the Sun. He said something which I will always
remember—when they face the side where the Sun is, that side is illuminated
by the Sun, making the front part of the suit extremely hot, while the backside
of the suit is freezing cold.

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Solar Radiation, Heat Balance, and Temperature

Now, it is a well-known fact that we live at the bottom of a huge pile of air.
Basically, air is around us all the time, though we cannot see it, but we can
definitely feel it. Let me show it to you with an illustration. Now, this is planet
Earth. Our Earth is surrounded by the atmosphere, so basically, this layer of
atmosphere does not allow important life-essential gases, including oxygen, to
go out into space. Similarly, it also doesn’t allow harmful excessive sun rays to
come inside. This layer of atmosphere that we just saw has some weight, and it
exerts some pressure on the Earth. That is what is known as atmospheric
pressure. Now, in the previous chapter, that is Chapter 8 – Structure and
Composition of Atmosphere, we came across some list of gases that exist in the
atmosphere. So here’s the list of gases, and the top three gases are more in
percentage, and I’ve also told you to remember them specifically, that is
nitrogen, oxygen, and argon. So anyways, coming to the present chapter, in
this, we are going to read about how and what leads to the heating and cooling
of the atmosphere. As I’ve told you, the atmosphere acts like a blanket that
protects the Earth from excessive sun rays, and it also blocks some heat and
some life-essential gases from going out into space. And we also know that not
every place on Earth receives the same amount of heat due to the natural tilt
in the Earth's axis that causes the sun rays to not reach all the places on Earth
equally. Because of this, the amount of heat received by different parts of the
Earth is not the same. When temperature is not the same everywhere, that
causes pressure differences in the atmosphere, that is, high pressure and low
pressure system, and this further leads to the transfer of heat from one region
to another by winds. So basically, these are the things that we are going to
study in this chapter: Solar Radiation – The energy emitted by the Sun in the
form of light and heat; Heat Balance – How the Earth maintains a balance
between the heat received from the Sun and the heat lost back into space; and
Temperature – How different parts of the Earth experience different
temperatures due to variations in solar radiation.

We are going to read in this chapter, so let's go to the first topic. Solar
Radiation—the meaning of the word solar radiation is the radiant energy
emitted by the Sun. Therefore, the energy that comes from the sun rays and is
received by the Earth is known as incoming solar radiation. Another term for
this is insolation. As I told you before, the Earth is surrounded by the

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atmosphere, and this layer of the atmosphere works as a blanket. Hence, we
can also say that this layer intercepts a huge quantity of the Sun’s energy.
Now, if you observe, the sun rays contain a mixture of electromagnetic
waves, ranging from infrared rays to ultraviolet (UV) rays. Among them,
UV rays are harmful to human beings, as direct contact with them may result in
skin cancer, sunburns, and other health issues. The atmosphere plays an
important role in filtering these harmful rays, preventing them from directly
reaching the Earth's surface. We all know that the Earth is a geoid
resembling a sphere, meaning it does not have a perfect shape—it has an
irregular shape. The amount of solar energy reaching the Earth's
atmosphere is approximately 1.94 calories per square centimeter per
minute. What does that mean? As I mentioned earlier, the atmosphere blocks
most of the sunlight, and only a small portion of the sun rays actually reach the
Earth. In the previous chapter, we learned about the five layers of the
atmosphere, with the outermost layer being the exosphere. The sun rays
first hit this outer layer, and not all of the radiation that reaches it is received
by the Earth's surface. This is because the atmosphere absorbs most of the sun
rays and reflects or sends a significant portion of them back into space. This
filtering mechanism helps maintain a balanced temperature system on
Earth, ensuring that our planet is neither too hot nor too cold throughout the
year. This was an overview of how much solar radiation reaches Earth. Another
important aspect is that the amount of sun rays reaching Earth's
atmosphere varies slightly throughout the year. You must have seen the
typical picture of how the Earth revolves around the Sun, where the orbital
motion appears to be a perfect circle. However, that is not true. The Earth’s
orbit is actually elliptical, meaning it follows an oval-shaped path with the
Sun positioned slightly off-center. This is the actual way in which the Earth
revolves around the Sun. One crucial point to mention is that after completing
one full revolution, Earth does not return to the exact same starting
point. There is a deviation in the elliptical path every year, and the reason
behind this deviation is the gravitational attraction of other planets. Large
planets like Jupiter and Saturn, which are much bigger than Earth, exert
gravitational forces that slightly affect Earth's orbital path. As a result, Earth
never returns to the same exact point after a full revolution. This is also
the reason why we need to adjust our calendar with leap years to account
for these orbital shifts. If I were to simplify this concept, just remember this:
Earth is not at the exact same spot in its orbit on your birthday every
year. I hope this concept is clear now. Additionally, the Earth’s speed in its
elliptical orbit is not constant. It is fastest when closest to the Sun and
slowest when farthest from the Sun. On 4th July, the Earth is farthest
from the Sun, a position known as aphelion, where the distance is about
152.6 million kilometers. On 3rd January, the Earth is closest to the Sun,

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a position called perihelion, where the distance is about 147.5 million
kilometers. As a result, the amount of incoming solar radiation, or insolation,
is greater on 3rd January and less on 4th July every year. Please remember
these dates. However, in reality, you will not feel any major temperature
difference on these dates. For example, on July 4th, you won’t necessarily
feel cooler temperatures, and on January 3rd, you won’t feel an
unusual increase in warmth. This is because the effects of aphelion and
perihelion get masked by other climatic factors, such as temperature
variations between land and sea, atmospheric circulation, and
pressure differences. These factors influence global temperatures more
significantly than the slight difference in Earth’s distance from the Sun.

The variability of insolation at the surface of the Earth refers to the changes in
incoming solar energy due to various factors. The amount and intensity of
insolation vary throughout the day, across seasons, and throughout the year.
For example, the afternoon is usually warmer than the morning or evening, and
summer is generally hotter than winter, monsoon, or spring. This variation in
solar energy occurs due to five main reasons. The first reason is the rotation
of the Earth on its axis, which takes approximately 23 hours and 56 minutes,
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causing day and night and leading to temperature differences, with nights
being cooler than days. The second reason is the angle of inclination of sun
rays; the sun's rays are direct and intense at the equator but become slanted
as they move toward the poles, reducing temperature as latitude increases.
The third reason is the length of the day, which is determined by the Earth's
rotation. However, due to the tilt of the Earth's axis, the duration of day and
night varies throughout the year, leading to the phenomenon of summer and
winter solstices, where the length of daylight changes. The fourth reason is
the transparency of the atmosphere, which determines how much solar
radiation reaches the surface. Factors such as volcanic eruptions, forest fires, or
pollution can make the atmosphere opaque, blocking solar radiation and
preventing heat from escaping, contributing to climate change. The fifth reason
is the configuration of land in terms of its aspect, which refers to the
influence of topography. Land heats up faster than oceans, contributing to
temperature variations and influencing overall climate patterns. The Earth's
axis is tilted at 66.5 degrees to the plane of its orbit around the Sun, affecting
insolation across different latitudes. During the summer solstice in June, the
Northern Hemisphere is tilted toward the Sun, receiving more solar
energy, making it summer there. By autumnal equinox in September, both
hemispheres receive equal sunlight, making day and night of equal length.
During the winter solstice in December, the Southern Hemisphere tilts
toward the Sun, receiving more energy, while the Northern Hemisphere
experiences winter. This explains why Australia, in the Southern Hemisphere,
experiences summer in December. By vernal equinox in March, both
hemispheres again receive equal sunlight, making day and night equal. These
variations in insolation due to Earth's rotation, axial tilt, and atmospheric
conditions play a crucial role in shaping global climate patterns.

The passage of solar radiation through the atmosphere is influenced by the

Earth's transparent atmospheric layers, which filter and regulate incoming solar
energy. The atmosphere plays a crucial role in preventing excessive heat from
escaping into space, making it essential for the survival of all living organisms.
As solar radiation travels through the atmosphere, it passes through various
gases, water vapor, dust particles, and ozone, primarily present in the
troposphere, the lowest layer of the atmosphere. Some of the incoming solar
energy is absorbed by these elements, altering the amount of radiation that
reaches the Earth's surface. Additionally, as sunlight interacts with atmospheric
gases, water vapor, and dust particles, it undergoes scattering, which leads to
visual phenomena such as the blue color of the sky and the red hues of
the rising and setting Sun. This scattering effect directly influences the

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colors we observe in the sky and is a fundamental consequence of the
atmosphere’s interaction with solar radiation.

Condensation
how condensation actually takes place, going a little deeper into the concept. A
very simple form of condensation is to take a bottle of cold water from the
fridge and keep it outside for some time. You'll notice water droplets start to
form on the outer surface of the bottle. So what do you think is happening?
Since the bottle has cold water inside, naturally, the bottle itself will be cold.
Now, we know that there is moisture in the air, which is also called humidity. If
we look closely at the outer surface of the bottle, air molecules in the
surroundings constantly hit the bottle from all directions. Since the bottle is
cold, the air right next to it also gets colder. This means the air, which already
has moisture, cannot hold any more water when it is closer to the surface of
the bottle, and that’s how moisture or water vapor transforms into liquid
droplets. Now, this is a tiny example, but the process is the same in the
formation of clouds and rainfall. The next interesting question to think about is:
what is inside a water droplet, or in other words, what is holding the water
together in the shape of a drop? The answer to that question is hygroscopic
condensation nuclei. It may sound like a big term, but it is fairly easy to
understand. If we study particle physics, the structure of a material in
decreasing form goes something like this: first, we have a solid block, which
could be any object around us. Then, we have molecules that give structure to
the solid block. Molecules are formed when two or more atoms combine, and
an atom is the smallest unit of matter. Inside an atom, we find subatomic
particles like protons, electrons, and neutrons. A combination of these
subatomic particles forms the nucleus, which is the center of an atom. The
plural of nucleus is nuclei. Essentially, everything around us comes down to this
single particle called nuclei. Therefore, when water droplets are formed during
condensation, there is a central nucleus that holds the water together in the
shape of a drop. So what is this nucleus? It consists of extremely tiny particles
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of dust, smoke, and ocean salt. These particles are called aerosols. Aerosols
have an amazing property of attracting and holding water molecules from the
surrounding environment, which is why they are called hygroscopic. So, if
anyone asks you what is inside a water droplet or what holds the water
together in the shape of a drop, you should be able to say that tiny particles of
dust, smoke, and salt absorb water molecules from the surrounding
environment. This is what is known as hygroscopic condensation nuclei.

Water in the Atmosphere

Now, when you hear the word water, immediately think of water vapor. Water
vapor is the gaseous state of water, and it is invisible to the human eye. In
previous chapters, we have learned that air contains water vapor, and it's due
to evaporation. You know the Sun's energy directly falls over land and ocean
bodies and makes them warm. Then, water molecules, after getting warm,
rapidly move and vibrate and then quickly escape into the atmosphere as
molecules of water vapor. Now, a similar process also takes place in plants; we
call it transpiration. Again, here also, due to the heat from the Sun, water
content from plants evaporates through its aerial parts such as leaves, stems,
and flowers. So, if you see, the important thing is heat. Heat from the Sun
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makes the evaporation process occur. Now, there is another natural
phenomenon called condensation and precipitation. Condensation is called the
reverse of evaporation. A good example is when you take a cold water bottle
out of your fridge and keep it out for some time. You'll notice a change in the
physical state of matter from gas into liquid—you'll see water droplets on the
outer side of the bottle. A similar thing happens in the atmosphere when warm
air rises due to evaporation, and as it goes higher and higher, it cools and loses
its capacity to hold water vapor. That's how clouds are formed. Water vapor in
the gaseous state turns into liquid. Once clouds are formed, the next step is
precipitation. That means the water in the cloud will fall due to surface tension,
and that's how rain, snow, and hail occur. So, if I have to quickly sum it up, it all
begins with evaporation, wherein liquid turns into gas—that is, water vapor.
After that, condensation takes place, wherein the water vapor, which is in the
gaseous state, turns back into liquid. Then, precipitation takes place, in which
water comes down to the surface as rain, snow, or sometimes as hail. Hail is
frozen rain. So, you see, now there's another physical state of matter, which is
solid. With this, we know that water is present in the atmosphere in three
forms: gaseous, liquid, and solid. More than anything else, you must
understand that there is a continuous exchange of water between the
atmosphere, and if you read here, it absolutely makes sense. It says the ocean
and the continents, through the process of evaporation, transpiration,
condensation, and precipitation, maintain a constant exchange of water
between the atmosphere.

Now, let's understand humidity in coastal regions. Always remember this point:
the amount of water vapor present in the air is known as humidity. That's why
when you go to any coastal region during summer, let's say Goa, Chennai, or
Puducherry, you will find these places to be very humid. You'll sweat like
anything because these places are at the same level as the sea level, and
that's how you can see the sea right in front of you. Again, the point is that
when you have a large ocean body, like a sea, in front of you, the evaporation
will be extreme. Evaporation is the rising of water molecules into the air, so
naturally, the surrounding region will be affected. In this case, it will have a lot
of humidity, and that is how coastal regions are humid.

Now, we are going to quickly understand these terms: absolute humidity,

relative humidity, air saturation, and dew point. The first one is absolute
humidity. I have told you the meaning of the word humidity, right? It is the
amount of water vapor present in the air. Now, when you look at the word
"absolute," it means complete or non-relative. In other words, we are talking
about the complete humidity present in the atmosphere. So, the formal
definition here says: the actual amount of water vapor present in the
atmosphere is known as absolute humidity.
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Now, if you recollect, water vapor is formed when water is warmed. To warm
the water, you need a high temperature, which means temperature is an
important factor in the formation of water vapor. However, when we calculate
absolute humidity, we do not take into account the temperature. That is
what the meaning of the word "absolute" implies—only considering the
humidity part in the atmosphere and not the temperature. Absolute humidity is
calculated by taking the weight of the water vapor per unit volume of air.

Now, let's look at relative humidity. In this, we need to take into account the
temperature as well. Hence, we can say that the percentage of water
vapor present in the atmosphere at a given temperature is known as
relative humidity.

As we know, temperature is an important factor in the formation of water

vapor. This means that if the temperature changes, moisture levels will also
change accordingly. That’s why at sea level, moisture is high because the
temperature is high. However, as altitude increases, temperature
drops, and air loses its capacity to hold water vapor. This is how we
conclude that a change in temperature directly affects relative
humidity.

Relative humidity is greater over the ocean because that is where

evaporation mostly occurs. On the other hand, over the continents, this is
not the case, making relative humidity lower over land areas.

The next one is saturation is something which dissolves or gets absorbed to a

certain degree since here we are talking about air saturation that means it is
the air that gets dissolved or absorbed now the question is what is the other
thing in which the air gets saturated since this chapter is mostly about water
vapor that means air is getting dissolved or absorbed by the water vapor so in
other words the air is incapable of holding any additional amount of water
vapor or moisture I'll explain this concept by taking a simple example take two
cups of water and imagine one of the cups contain hot water and the other is
cool let's assume that the right cup has hot water and the left has cold water
you'll notice that the right cup is steaming because it contains the hot water
now you will not actually see any water vapor because the cups are not
covered rather you will just see that the water vapor is evaporating now
evaporation also takes place in the left cup but at a very less rate compared to
the right cup now let's put a couple on these two cups I'll draw some arrows
that will represent different rates of evaporation since the warm cup is on the
right side and it is evaporating faster I'll draw three arrows which represents
the rate of evaporation to be three times faster similarly in the left cup I'll draw
one arrow which represents the rate of evaporation is three times lesser than

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the right cup now I have just give the numbers 1 & 3 randomly because the
actual numbers are not important the only thing that you need to understand is
that the right cup containing warm water evaporates more quickly than the
cold water so in this example both cups are half-empty meaning the remaining
portion of the cups contain air since both cups are evaporating at different
grades water vapor will start to build up in the air above each cup however in
the right cup the air is not able to accommodate as much water vapor as in the
left cup this happens because air is saturated in both cups but you will find
more water vapor in the right cup which has high temperature that means the
air in the right cup has saturated or dissolved and cannot hold any more
moisture that's why it condenses and returns to liquid form with this example I
hope you have understood what air saturation means.

Now let's understand dew point. Basically, you just have to understand what
dew is. You have seen it on grass blades, plant leaves, and stones during cold,
chilly mornings. Dew consists of water droplets found on cooler surfaces,
formed from moisture, which is water vapor. Moments back, we read about air
saturation, where we saw that there is a point at which the air becomes
incapable of holding any additional amount of water vapor or moisture. Now,
that particular point—where the air cannot hold any more water vapor—
because right after that, the water vapor turns into liquid droplets, is called the
dew point. This is how dew is formed. So, the dew point is the exact
temperature at which air becomes fully saturated, leading to condensation.
Dew is basically water in the form of droplets, and it exists due to
condensation. Since condensation is the reverse of evaporation, dew forms
when warm, moisture-laden air cools down to its saturation point, causing
water vapor to condense into visible droplets.

Evaporation and condensation are responsible for the continuous interaction of

water and the atmosphere. The name of this chapter, "Water in the
Atmosphere," perfectly reflects this process. Evaporation converts water into
water vapor, meaning it changes from a liquid to a gaseous state, while
condensation is the reverse process, where water vapor converts back into
liquid form. The temperature at which water starts evaporating is called the
latent heat of vaporization. Condensation is formally defined as the
transformation of water vapor into water, which means the gaseous state
changes back to liquid, making it the reverse of evaporation. During
condensation, heat is lost. When the air cannot hold any more water vapor or
moisture, the excess water vapor turns into liquid. However, if the water vapor
condenses directly into a solid form instead of liquid, this process is known as
sublimation. A perfect example of sublimation is hail, known as "Oly" in Hindi.
Hail consists of ice pellets that are spherical or sometimes conical in shape.

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Since hail is a piece of ice, it exists in a solid state, making it an example of
sublimation, where water vapor directly transforms into a solid form.

Condensation is a process that can be easily observed in everyday life. A

simple example is taking a cold water bottle from the fridge and placing it
outside for some time. Soon, water droplets start forming on the outer surface
of the bottle. This happens because the cold water inside makes the bottle
itself cold. The air around the bottle contains moisture, also known as humidity.
When air molecules near the bottle come in contact with its cold surface, they
cool down, reducing their ability to hold moisture. As a result, the excess water
vapor condenses into liquid droplets on the bottle’s surface.

For condensation to take place, four main conditions must be met:

1. Volume of Air – Air carries moisture, and when a given volume of air
exceeds its ability to hold more moisture, water vapor transforms into
liquid.
2. Temperature – Condensation requires a drop in temperature. When warm,
moisture-laden air comes into contact with a cooler surface or
environment, it loses its ability to hold moisture, leading to condensation.
3. Pressure – Pressure plays a crucial role in condensation. In a gaseous
state, molecules are far apart and move freely. To turn gas into liquid or
solid, high pressure is needed to bring molecules closer. Conversely,
evaporation requires low pressure as molecules move farther apart. This
principle is also observed in atmospheric systems—cool air (high pressure)
moves towards warm air (low pressure), causing condensation.
4. Humidity – Humidity refers to the moisture content in the air. Warm air
holds more moisture, and when it meets a cooler temperature and high
pressure, condensation occurs, transforming water vapor into liquid.
Among these four conditions, temperature decrease is the most crucial
factor. Without a drop in temperature, condensation cannot occur. Once
condensation happens, water vapor in the atmosphere transforms into dew,
frost, fog, and clouds, meaning it changes from a gaseous state into either
liquid or solid form.

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Dew is the first liquid form that appears after condensation, where water vapor
transforms into tiny water droplets. The temperature at which dew forms is
called the dew point. Dew can be seen on stones, grass, and plant leaves,
especially during long winter nights. Dew forms only if the temperature is
slightly above 0°C. If the temperature drops to freezing or below, ice forms
instead of dew. More moisture in the air increases the chances of condensation,
leading to dew formation. If strong winds are present, cold, dense air cannot
settle down, making it difficult for condensation to occur. Thus, dew formation
requires cool temperatures, high humidity, and still air for condensation to take
place efficiently.

Frost is another form of condensation, commonly seen in refrigerators and cold

outdoor surfaces. Frost forms when water vapor directly turns into ice, meaning
the temperature must be below the freezing point of 0°C. To put this into
perspective, the temperature must also be below the dew point because, unlike
dew, which forms water droplets, frost consists of tiny ice crystals. The ideal
conditions for frost formation are the same as those for dew, except that the air
temperature must be below freezing.

Fog and mist are also forms of condensation. Fog is essentially a cloud that
forms very close to the ground. The primary difference between fog and mist
lies in visibility. If visibility is less than one kilometer, it is classified as fog; if
visibility exceeds one kilometer, it is considered mist. In urban and industrial
areas, air pollution plays a significant role in fog formation. Smoke and
pollutants act as condensation nuclei, attracting moisture and leading to
denser fog or mist. When fog mixes with smoke, it is called smog. A well-known
example is the severe smog in Delhi, which causes major air pollution issues.

Both fog and mist are a form of condensation, which means they contain water
droplets in the air, as condensation is the reverse of evaporation where water
vapor (gas) transforms into liquid. In both fog and mist, the surface tension of
these water droplets is low, which causes them to fall slowly. However, in the
case of rainfall, the surface tension is high, making the droplets fall quickly as
rain. Now, both fog and mist contain tiny particles of dust, smoke, and salt,
known as hygroscopic condensation nuclei, which help in holding the water
droplets. This means that at the most basic level, both fog and mist have these
nuclei at their center. To understand the difference between fog and mist, we
need to look at what happens around these nuclei. In mist, the layer of
moisture around the nuclei is thick, which makes mist appear whiter and
denser. That is why, when you walk on a misty morning, you may notice water
droplets forming on your jacket. On the other hand, fog is basically a cloud at
ground level and is drier than mist. This means the moisture layer around the
nuclei in fog is not as thick. Since fog contains less moisture, its tiny water
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droplets remain suspended in the air for a longer time, causing poor visibility.
The lesser the moisture content, the longer the nuclei float in the air, making
fog denser and leading to reduced visibility. In simpler terms, mist has more
water content and appears thicker, while fog has less moisture, making it
lighter but causing greater visibility issues.

The fourth form of condensation is clouds. Many times, it has been mentioned
that both rainfall and clouds are a result of condensation. Now, let’s quickly
understand how clouds are formed. When we look at a cloud, it appears as a
white, fluffy, gaseous mass moving around in the air. However, clouds are
actually a large collection of tiny water droplets consisting of liquid water and
ice crystals formed by the condensation of water vapor in free air. The cloud
formation process begins with the Sun heating the Earth's surface, which in
turn warms the surrounding air. This warm air rises from the ground and carries
moisture along with it. As altitude increases, the temperature decreases, which
leads to the cooling of the rising warm air. As the temperature drops, the air
becomes incapable of holding excess moisture. Now, another important factor
to consider is the presence of tiny particles of dust, smoke, and salt in the air,
known as aerosols. These aerosols act as hygroscopic condensation nuclei,
meaning they have the ability to attract water molecules. As the air cools,
excess water vapor condenses onto these condensation nuclei, forming tiny
cloud droplets. Since aerosols are present in large quantities in the
atmosphere, they provide the necessary surface for water vapor to condense.
When enough water molecules accumulate on these nuclei, cloud droplets are
formed. These droplets are extremely small, and when they gather in large
numbers, they form a big, fluffy cloud, which can weigh several tons. Despite
their weight, these cloud droplets are so tiny that they remain suspended in the
air. When the cloud droplets combine to form larger drops or ice crystals, they
eventually become too heavy. Due to surface tension, these heavier droplets
fall from the sky as rain.

Clouds are grouped based on height, size, density, and transparency, and the
first type is cirrus clouds. These clouds are formed at high altitudes, around 8
to 12 kilometers, which is roughly the height of Mount Everest. They appear
thin and feathery, and because they are formed at such high altitudes, the
temperature is very low, so they consist of ice crystals rather than water
droplets. The second type is cumulus clouds, which form at a height of 4 to 7
kilometers, lower than cirrus clouds but still quite high in the sky. These clouds
are fluffy and cotton-like, with a flat base that can resemble a cauliflower.
Cumulus clouds often appear in scattered patches, and though they may not
always produce rain, if they gather together and grow in size, they can lead to
heavy rainfall. Since cumulus clouds are larger than cirrus clouds, they contain
more water vapor or ice crystals. The third type of cloud is the Stratus cloud.
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"Stratus" means existing in layers, so these clouds appear as horizontal,
layered formations that cover large portions of the sky. Stratus clouds are
classified as low-altitude clouds, typically found at a height of less than 2
kilometers. They are usually white or gray in color, and because they are at a
lower altitude, they can sometimes descend to the Earth's surface as mist or
fog. In a sense, Stratus clouds are similar to fog, though they don’t quite reach
the ground. These clouds block sunlight, often making the day appear dull and
overcast. The fourth and final type of cloud is the Nimbus cloud. Nimbus clouds
are typically black or dark gray and also form in layers, similar to Stratus
clouds, but they are distinct in some ways. These clouds form at low altitudes,
around 3 kilometers or so, and sometimes even closer to the surface. Their
dark color indicates that they are dense and contain a large amount of water
vapor, which prevents sunlight from reaching the Earth's surface. Nimbus
clouds are thick and do not have a specific shape, and their density makes
them capable of bringing heavy rain.

Now, let's move on to the next topic: precipitation. So far, we’ve learned about
condensation. Precipitation is a direct result of condensation. While
condensation is the process in which water vapor transforms into water or a
solid, precipitation refers to when these condensed water droplets fall to the
Earth's surface due to surface tension. The line, "After the condensation of
water vapor, the release of moisture is known as precipitation," perfectly
describes this. Precipitation can occur in both liquid and solid forms. If it’s in
liquid form, we call it rainfall, which happens when the temperature is above
the freezing point. On the other hand, if precipitation occurs in solid form, we
call it snowfall or hailstones, and this happens when the temperature is below
the freezing point. Just remember that for snowfall and hailstones, the
temperature has to be below freezing, which is why they generally occur at
higher altitudes, where temperatures are naturally colder.

Now, let's dive into the topic of types of rainfall. Rainfall is classified into three
main types, and the first one is convectional. The term "convectional" might
remind you of convection currents, which refer to the transfer of heat energy
from one place to another. These currents can occur in gases, liquids, and even
in molten rocks. For instance, convection currents are found in the Earth's
mantle, where heat from magma rises toward the lithosphere. In the
atmosphere, convection currents are formed when the Sun heats up the land
surface. This warming of the land also heats the surrounding air, causing the
warm air to rise and reach the cooler troposphere.

With this understanding of convection, convectional rain occurs when the

Sun's energy heats the land surface and the surrounding air. As the warm air
rises, it forms convection currents, transferring heat energy upward. As the air
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rises, it loses heat and reaches cooler regions in the sky, causing condensation
and cloud formation. Once clouds are formed, rainfall takes place. The ideal
conditions for convectional rain include a warm climate, such as during the
summer season, with the equatorial region being the most common location,
as it receives direct sunlight throughout the year. Convectional rain is
particularly common in the interior parts of continents because the land heats
up faster than water. Additionally, convectional rain is more prominent in the
northern hemisphere, where there is more land, meaning the northern
hemisphere heats up faster during summer than the southern hemisphere.

Orographic rain is a type of rainfall that occurs due to the presence of

mountains. The term "orographic" is related to autogenic processes, and we
previously encountered the term "orogenic process" in diastrophism, which
refers to mountain-building processes. When crustal plates move horizontally,
they either come closer, move apart, or slide past each other. Mountains are
formed when two crustal plates come closer, with one plate sliding under the
other, causing the land surface to elevate. This process plays a crucial role in
orographic rain. The key element in orographic rain is the presence of
mountains. The land and water surfaces heat up due to solar energy, but water
surfaces experience intense evaporation. Warm air containing water vapor rises
but does not move in a perfectly straight pattern due to horizontal air currents.
According to the laws of thermodynamics, heat moves from areas of higher
temperature to areas of lower temperature, which determines the movement of
warm air. Land surfaces heat up and cool down faster than water, and the top
of a mountain heats and cools faster than the valley floor, making mountains
relatively cooler. As warm air from the ocean rises due to evaporation, it moves
towards colder regions, such as the mountaintops, before reaching the cold
troposphere at around 10 to 12 kilometers in altitude. The warm air is pushed
upwards along the mountain slope by horizontal winds. As it ascends,
atmospheric pressure decreases, causing the air to cool and the water vapor to
condense, forming clouds and leading to rainfall. Once the air reaches the
summit and descends, the temperature rises, increasing its capacity to hold
moisture, preventing rain on the leeward side of the mountain. This dry area is
known as the rainshadow region. Orographic rain occurs when warm air is
forced to rise over a mountain or hill, cools, condenses, and forms rain. In the
Indian subcontinent, orographic rain is observed in the Western Ghats when the
southwest monsoon winds encounter the hills and mountains. Similarly, the
Himalayan mountain range blocks monsoon winds, leading to heavy rainfall at
higher elevations. The 2013 Kedarnath disaster, caused by a sudden cloudburst
resulting in flash floods and landslides, is a significant example of orographic
rain.

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Cyclonic rain is a type of rainfall caused by cyclonic activity, which involves a
large-scale air mass rotating around a low-pressure zone. Air always moves
from high-pressure to low-pressure areas, and this movement is driven by
temperature differences. Sunlight does not heat all parts of the Earth's surface
equally, leading to variations in pressure. Warm air holds moisture, while cold
air is dry. When a warm air mass meets a cold air mass, the boundary between
them is called a front. There are two types of fronts: the warm front, where air
rises, and the cold front, where air sinks. Since warm air is lighter than cold air,
it rises gently over the cooler, denser air. As the warm air ascends into the
troposphere, where temperatures are lower, it begins to cool. The moisture in
the warm air condenses, forming clouds, and eventually leads to rainfall.
Cyclonic rainfall occurs when two air masses of different temperatures collide,
causing the warm air to rise rapidly, lose heat, condense its moisture, and
produce rain.

world distribution of rainfall

Different regions of the Earth receive varying amounts of rainfall throughout

the year and in different seasons. This variation is primarily due to differences
in solar heating, evaporation, and atmospheric circulation patterns. Rain is a
result of condensation, which occurs when there is enough evaporation.
Evaporation is driven by the Sun’s heat, which warms the Earth's surface,
causing warm air to rise and condense. As we move away from the equator
towards the poles, rainfall steadily decreases because humidity levels drop.
This happens because temperature decreases at higher latitudes, and cold air
holds less moisture than warm air. Coastal areas receive more rainfall than the
interiors of continents because evaporation is higher over large water bodies
like oceans and seas, making coastal regions more humid. In latitudes between
35° and 40° north and south of the equator, rainfall is heavier on the eastern
coasts and decreases towards the west. However, between 45° and 65° north
and south, westerlies bring rain first to the western margins of continents
before decreasing towards the east. In regions where mountains run parallel to
the coast, rainfall is higher on the windward side and decreases towards the
leeward side due to orographic rainfall.

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World Climate and Climate Change

Broad Classification of Climate

Climate is classified into three main categories:

1. Empirical Classification – Based on observed and recorded data such as

temperature, rainfall, and pressure over time. Example: Meteorological
departments maintaining climate datasets.

2. Genetic Classification – Focuses on the causes or origins of climate

variations, such as solar radiation, atmospheric pressure systems, and wind
patterns.

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 3. Applied Classification – Climate classification for practical applications,
such as agriculture, construction, and energy planning, to support
economic and social decision-making.

Koeppen’s scheme of classification of climate.

Wladimir Köppen, a Russian-German climatologist, classified the world's

climate based on its relationship with vegetation. His goal was to create a chart
using formulas and notations to define climatic boundaries that closely
matched natural vegetation patterns. By analyzing regional plant life, he
identified distinct climate types and categorized them into groups with specific
traits.

Koeppen’s Climatic Classification

Playlist

Climate change -

It is important to understand that weather changes daily, while climate remains

stable over long periods. Weather is observed over short durations, whereas
climate reflects the atmosphere's long-term behavior. The climate we
experience today has likely prevailed for the last 10,000 years with minor
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fluctuations, as there have been no major physiographical or geological
changes. Around 8000–7000 BCE, early humans, living in small populations,
relied on wild plants and animals before settling down, domesticating animals,
and practicing agriculture. Their settlements were influenced by climatic
patterns, which later grew into cities and towns. The overall climate has
remained stable, with only minor changes. Significant shifts would have forced
early humans to migrate. Today, slight climate variations result from human
activities like burning fossil fuels, leading to pollution and waste generation.
Climate change, a pressing issue, has been both a natural process and
increasingly human-driven in recent times. Natural evidence, such as glacier
movements shaping landforms and sediment deposits in glacial lakes, shows
historical climate fluctuations. Tree rings also reveal past wet and dry periods,
proving climate has always been evolving.

In higher latitudes, steep landforms were shaped by glacier movement and

melting over time. As temperatures changed naturally, glaciers melted from
their lower ends, creating friction with the land beneath and eroding the
bedrock, forming steep landforms. Sediment deposits in glacial lakes further
confirm past warm and cold periods, as glaciers erode rocks into tiny sediments
that accumulate in these lakes. Tree rings also provide insights into past
climate variations, with larger rings indicating colder years and smaller rings
indicating warmer years.

A relevant example of climate change in India is the Rajasthan desert. Around

8000 BCE, Rajasthan experienced a wet and cool climate, meaning it once
received heavy rainfall. The desert’s sand could have resulted from either
massive geological changes due to the movement of Earth's lithosphere or the
erosion and transportation of sediments by rivers. This suggests that a
significant part of Rajasthan may have once been under a river, covered with
vegetation. This example reinforces the idea that climate change is a natural
and continuous process, and the climate we experience today has likely
prevailed over the last 10,000 years with minor fluctuations.

——-

about this little paragraph I'll make a separate video on Earth's geological
timescale in that I'll explain what the earth went through at different period of
time and it will give you a broad understanding about the Earth's history with
respect to time and relationships of events alright

Climate in the Recent Past (Last 100–200 Years)

The Industrial Revolution, which began in the 19th century (around 1880),
marked a turning point in climate change. Since then, Earth's temperature has
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risen continuously. While the Industrial Revolution made life easier, it came at
an environmental cost. It relied on three key natural resources: iron, coal, and
water—iron for machinery, water for power and transport, and coal for steam
engines. The burning of vast amounts of coal, a fossil fuel, released enormous
amounts of smoke, leading to air pollution and climate change—a problem
that persists and has intensified today.

Global temperature data since the Industrial Revolution show a steady

increase, with even a 1°C rise significantly impacting oceans, land, and
the atmosphere. Historical climate records highlight key events:

1990s – Warmest temperatures of the century; severe global floods.

1960s–70s – Extreme drought in the Sahel region (a transition zone below
the Sahara Desert, spanning Mauritania, Mali, Niger, Chad, and Sudan).
1930s – Severe drought in the Great Plains of the USA, leading to massive
crop failures, economic decline, and migration.
10th–11th centuries – Europe experienced warm, wet, cold, and dry
periods.
The Ice Age, when much of Earth was covered in glaciers, lasted until 11,700
years ago. Since then, Earth has been in the Holocene or interglacial
period, with temperatures gradually rising. However, since the Industrial
Revolution, human activities have accelerated climate change, pushing
temperatures upward at an alarming rate.

Causes of Climate Change

Climate change is driven by four main factors, broadly categorized into

Astronomical Causes (external, beyond Earth’s control) and Terrestrial
Causes (internal, occurring within Earth’s atmosphere).

1. Sunspots: Astronomical Causes (Related to celestial or planetary

factors)

Sunspots are dark, cooler regions on the Sun’s surface with lower
temperatures than the surrounding solar surface.
The Sun’s surface temperature is around 6,000 Kelvin, whereas
sunspots are cooler at 3,700 Kelvin.
Increased sunspots → Cooler and wetter climate on Earth.
Decreased sunspots → Warmer and drier conditions due to higher
solar radiation reaching Earth.

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 Since some sunspots are larger than Earth, their position relative to
Earth can impact the amount of incoming solar radiation, affecting
climate patterns.
2. Milankovitch Oscillations (Astronomical Cause of Climate
Change)

Milankovitch Oscillations refer to variations in Earth's orbital motion

around the Sun. Since this is an astronomical factor, it is beyond human control
and affects Earth's climate over long geological periods.

Key Aspects of Milankovitch Oscillations:

1. Earth’s Orbit is Elliptical, Not Circular

The common image of Earth's orbit as a perfect circle is incorrect—it

follows an elliptical path where the Sun is closer to one end.
This elliptical orbit constantly shifts due to gravitational
interactions with massive planets like Jupiter and Saturn.
Because of these shifts, Earth does not return to the exact same
starting point in its orbit every year.
2. Effect of Earth's Distance from the Sun

The Earth's speed in its orbit varies depending on its distance from the
Sun:
Aphelion (Farthest from the Sun - July 4th)
Distance: 152.6 million km
Solar radiation is slightly lower
Perihelion (Closest to the Sun - January 3rd)
Distance: 147.5 million km
Solar radiation is slightly higher
3. Impact on Climate

This variation in solar energy received is called insolation (incoming

solar radiation).
Even though this change is not immediately noticeable in daily life
due to atmospheric factors, over long time scales, it contributes to
climate fluctuations.
These oscillations have been linked to glacial and interglacial
periods (ice ages and warm periods).
Milankovitch Oscillations help explain why Earth has long-term climate
changes and why ice ages occur periodically.

3. Volcanism (Terrestrial Cause of Climate Change)

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 Volcanism falls under terrestrial causes because volcanoes exist on Earth's
surface.
Volcanic eruptions release aerosols into the atmosphere, which remain for a
long time and cause a dull and gray sky.
These aerosols block incoming solar radiation, reducing the amount of
sunlight reaching Earth.
Volcanic eruptions emit gases and particles such as:
Carbon dioxide (CO₂)
Sulfur dioxide (SO₂)
Hydrochloric acid (HCl)
Hydrofluoric acid (HF)
These emissions can poison lakes and rivers, turning them into acidic
pools that dissolve marine organisms.
Aerosols also block outgoing radiation, contributing to climate change.
4. Increase in Greenhouse Gas Concentration (Terrestrial
Cause of Climate Change)

Greenhouse gases trap heat within Earth's atmosphere, preventing it from

escaping into space, leading to global warming.
The major greenhouse gases include carbon dioxide (CO₂), methane
(CH₄), nitrous oxide (N₂O), and water vapor.
Unlike other atmospheric gases, CO₂ levels have been rising due to
burning fossil fuels like diesel and petrol, especially since the Industrial
Revolution (mid-18th century).
This increase in CO₂ is an anthropogenic effect, meaning it results from
human activities.
Since this occurs within Earth's atmosphere, it is classified as a terrestrial
cause of climate change.
now if you're interested in watching a video on understanding the greenhouse gases and
greenhouse effect then I have
a video on it as well I'll put the link of that video in the description just have a look at it
how does climate change affects humans and nations both socially and economically ?
Climate change is real, and it is primarily caused by human activities like
burning fossil fuels, which release greenhouse gases such as carbon dioxide,
methane, and nitrous oxide. These gases trap heat in the Earth's atmosphere,
making the planet warmer. Since the Industrial Revolution, carbon emissions
have risen due to increased machine usage and deforestation, which reduces
the Earth's ability to absorb carbon dioxide. Scientists warn that if global
temperatures rise beyond 2°C, ice at the North and South Poles will melt,
causing sea levels to rise. When sea levels rise, coastal areas will face floods,
hurricanes, and destruction, leading to mass migration. For example, in
Bangladesh, rising water levels in the Bay of Bengal are pushing people from

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low-lying areas to cities, increasing population pressure, unemployment, and
poverty. This internal migration leads to overcrowding, strain on resources, and
economic inequality. The melting of Arctic ice and large icebergs, like the
trillion-ton iceberg that broke off Antarctica, further accelerates sea-level rise,
putting low-lying regions such as parts of the United States, India, and
Bangladesh at risk. The consequences of climate change are not just
environmental but also social and economic, affecting millions of people
worldwide.

Oceanography
Planet Earth is also called the blue planet due to the abundant water on its surface. In
the entire solar system, liquid water is a rare commodity, with over 70% of it found on
Earth's surface. In fact, human bodies, plants, and animals are mostly made up of
water, making it an essential and rare resource. The first topic in this chapter is the
hydrological cycle, also known as the water cycle. The water cycle describes the
continuous movement of water on, above, and below the Earth's surface through the
processes of evaporation, condensation, and precipitation. Essentially, water is being
reused as it moves from the ocean to the land and back, forming a cycle that has been
ongoing for billions of years. Since Earth is estimated to be 4.5 billion years old, this
cycle has played a crucial role in sustaining life. If the cycle were to stop, living beings
would not receive sufficient water, which could have detrimental effects on all life
forms. The distribution of water on Earth is quite uneven, with only 3% of it being fresh
water, while the remaining 97% is ocean water, which is too salty for human
consumption. Of the 3% fresh water, 69% is found in glaciers, 30% exists as
underground freshwater extracted through borewells, and less than 1% is located in
lakes, rivers, and swamps. Additionally, some regions on Earth have an abundance of
water, while others have very limited quantities, making water a rare and highly
exploited resource. The hydrological cycle ensures the circulation of water within
Earth's hydrosphere in liquid, solid, and gaseous forms. Evaporation is the process
where water is converted into water vapor with the help of heat. After evaporation,
condensation occurs, turning water vapor into liquid or solid depending on the
temperature. This is followed by precipitation, which can occur in the form of rainfall
(liquid state) or snow and ice pellets (solid state). This is how water circulates within
the Earth's hydrosphere. While the renewable water supply on Earth remains constant,
the demand for water is increasing tremendously, leading to water crises in different
parts of the world.
The next topic is the relief of the ocean floor. In geography, "relief" refers to the
topography of an area, so the relief of the ocean floor means the topography or
physical features of the ocean bed. If we take a model of planet Earth and create a
depression on its outer layer, that is where oceans are formed. Essentially, oceans are
the great depressions of Earth's outer layer where water accumulates. If we look at the
world map, continents are not necessarily merged with each other, except for Europe
and Asia, which are connected. However, continents like North America, South
America, Africa, Australia, and Antarctica remain separate. In contrast, oceans
naturally merge into one another, making them interconnected. Despite this natural
connection, geographers have divided the world's oceanic part into four major oceans:
the Pacific, Atlantic, Indian, and Arctic. Various seas, bays, gulfs, and other inlets are
part of these four large oceans because all rivers and inland waterways eventually
drain into a sea, which in turn is part of the ocean. If one were to dive into an ocean,
they would find that the major portion of the ocean floor lies between three to six
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kilometers below the sea level. It is important to note that sea level refers to the
surface of the ocean, while the ocean floor lies much deeper. Upon reaching the ocean
floor, we can observe that the land beneath the water has similar physiographic
features as seen on landmasses. This means the ocean floor contains large mountains,
deep trenches, and vast plains, just like the Earth's surface. The formation of these
underwater features is primarily due to tectonic activities, volcanic eruptions, and
depositional processes. This indicates that the underwater world has landscapes
similar to those found on land.
The ocean floors can be divided into four major divisions. The first one is the
continental shelf. The top layer of the Earth is called the crust, which is
divided into continental crust and oceanic crust. The continental crust is
the part on which we live. Suppose you go to a beach and start walking
towards the water; you will notice that the water level appears to rise.
However, in reality, the land gradually descends underwater. Then, all of a
sudden, the continental crust ends at a very steep slope. This point is called
the continental shelf break. The region between the continental shelf break
and the beginning of the beach is known as the continental shelf. This region
is the shallowest part of the ocean. The width of the continental shelves
varies from one ocean to another. The average width of a continental shelf is
about 80 kilometers. These shelves are almost absent or very narrow
along some coastal margins, such as the coast of Chile and the west coast
of Sumatra. On the contrary, the Siberian Shelf in the Arctic Ocean is the
largest in the world, stretching 1,500 kilometers in width. The depth of
the shelves also varies. In some areas, it may be as shallow as 30 meters,
while in others, it can be as deep as 600 meters. On a beach, when we walk
towards deep water, the land gradually descends. Beaches are composed of
sediments. In addition, rivers, glaciers, and winds carry massive
amounts of sediments from the land. Naturally, these sediments follow the
same path and get deposited on the continental shelf. In other words, the
continental shelves are covered with sediments brought by rivers,
glaciers, and wind from the land. Over time, these massive sedimentary
deposits on the continental shelves become a source of fossil fuels.

The second division of the ocean floor is the continental slope. Using the
same illustration as for the continental shelf, the continental shelf break
marks the point where the shelf ends and a steep slope begins. This steep
slope is called the continental slope, which connects the continental shelf
with the ocean floor. The gradient of this slope varies between 2 to 5
degrees, and its depth ranges from 200 to 3,000 meters. The continental
slope boundary marks the transition from continental crust to oceanic
crust. This region is also characterized by the presence of canyons and deep
trenches.

The third division of the ocean floor is the deep-sea plain. Once the
continental slope ends, a horizontal and flat underwater region begins.
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This is known as the deep-sea plain. It is generally found between the foot
of the continental slope and an oceanic ridge or trench. An oceanic
ridge is an uplifted landform similar to a mountain, while a trench is a
long, narrow depression in the ocean floor. Deep-sea plains are the
flattest and smoothest regions in the world, with depths ranging from
3,000 to 6,000 meters. These plains are covered with fine-grained
sedimentssuch as clay and silt, which settle over time, making the ocean
floor extremely smooth.

The fourth major division of the ocean floor is the oceanic deeps or trenches.
These are the deepest parts of the ocean, resembling long, narrow ditches or
cavities in the ocean bed. The most well-known trench is the Mariana Trench,
which reaches a depth of 10,994 meters below sea level, making it the deepest
point on Earth. Oceanic trenches are formed due to a process called
subduction. Subduction is a geological process where one tectonic plate moves
under another, causing the ocean floor and outermost crust to bend and form a
V-shaped depression. This can occur in three scenarios: between two oceanic
plates, between an oceanic plate and a continental plate, or between two
continental plates (although this usually forms mountains rather than
trenches). So far, 57 deep oceanic trenches have been explored: 32 in the
Pacific Ocean (highest number), 19 in the Atlantic Ocean, and 6 in the Indian
Ocean. These four major divisions—continental shelf, continental slope, deep-
sea plain, and oceanic trenches—constitute the hidden world at the bottom of
the ocean.

Now we will look at some minor relief features. The first one is mid-oceanic
ridges. The meaning of the word "ridge" is a long, narrow hilltop, like a
mountain range. It is basically an elongated, uplifted landform, and since we
are talking about mid-oceanic ridges, it means these are located on the ocean
bed. Essentially, a mid-oceanic ridge is an underwater mountain system formed
by plate tectonics. Another term for this phenomenon is "seafloor spreading."
The Earth is divided into four layers: the crust at the top, followed by the
mantle, then the outer core, and finally the inner core. Just below the crust, the
mantle consists of hot molten magma, making it highly volatile. A convection
current occurs in the mantle, where hot molten magma continuously rises and
sinks in a circular pattern. This convection current in the mantle forces magma
to rise and spread the oceanic crust, uplifting it and creating an opening. The
magma then quickly emerges onto the ocean floor. Due to the cool ocean
temperatures, the deep magma cools, crystallizes, and forms new crust,
resulting in the formation of an uplifted landform known as a mid-oceanic ridge.
This process causes two oceanic plates to move away from each other due to a
hydrothermal vent beneath the oceanic crust, also called an oceanic volcano.
The eruption of magma leads to the spreading of the ocean floor, forming
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oceanic ridges. The mountain ranges in these ridges can have peaks as high as
2,500 meters, with some even rising above the ocean surface. A good example
of this is Iceland, which is part of the Mid-Atlantic Ridge.

The second minor relief feature is sea mountains. A sea mountain is a mountain with
pointed summits rising from the seafloor that does not reach the surface of the ocean.
If it does emerge above the ocean surface, it becomes an island or a cliff rock. Sea
mounts are volcanic in origin, meaning they are commonly found near the boundaries
of Earth's tectonic plates. The Earth's crust is divided into several plates that float over
the mantle, and at the boundaries of these tectonic plates, sea mountains are formed.
However, there is a key point to note—at these boundaries, two things can happen.
First, the tectonic plates may move away from each other, leading to seafloor
spreading and the formation of oceanic ridges. Second, the tectonic plates may move
towards each other, causing one plate to subduct beneath the other. This subduction
process results in tectonic plate collisions, forcing one plate to move under another,
which in turn causes magma to rise from the mantle. When magma rises from the
mantle, a vent is naturally created, forming an undersea volcano. These volcanoes on
the ocean floor eventually become sea mounts. Essentially, sea mounts are individual
volcanoes on the ocean floor. They tend to be circular or conical in shape, similar to
volcanoes on land. Their height can range between 3,000 and 4,500 meters. A well-
known example is the Emperor Seamount chain, an undersea mountain range in the
Pacific Ocean, located near Hawaii.
The third minor ocean relief feature is submarine canyons. A canyon is a deep, narrow
valley with steep sides, typically formed due to weathering and erosion caused by
rivers. They are often referred to as V-shaped valleys because the river’s strong
stream cuts deep into the land, forming a steep-sided valley. Submarine canyons are
similar but are found underwater at the junction between the continental shelf and the
continental slope. They are formed when large rivers with strong streams drain into
the sea, carrying massive amounts of sediment. The high water pressure of these
rivers cuts deep into the seabed, creating deep, narrow channels known as canyons.
Due to their complex topographic features, submarine canyons serve as major
reservoirs of marine biodiversity.
The fourth minor ocean relief feature is Guyot (pronounced as "Gyo"). A Guyot
is an undersea mountain, specifically a seamount with a flat top. Since it is a
type of mountain, it is of volcanic origin. Volcanic activity forms all kinds of
underwater mountains. Guyots are usually found in deep ocean basins. The
reason the top of the mountain is flat is due to erosion by waves, which
destroys the peak of the seamount, giving it a flattened shape. Guyots are
most commonly found in the Pacific Ocean. These underwater structures stand
at least 3,000 feet above the seafloor, and the diameter of the flat top is at
least 660 feet.

The fifth and last minor relief feature of the ocean floor is Atoll. These are low
islands found in tropical oceans, consisting of coral reefs surrounding a central
depression. The formation of an atoll begins with an underwater mountain
created due to volcanic eruption, which eventually pierces the ocean surface.
Over time, a coral reef forms around this volcanic island or seamount. As more
time passes, the volcanic island sinks due to erosive activities of ocean waves,
making the top layer of the mountain flat—these are known as Guyots.

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Eventually, when the volcanic island completely submerges, all that remains is
the surrounding coral reef. The central depression left behind is called a
lagoon. This lagoon may or may not be connected to the sea. If it is
connected, it will be highly saline; if not, it can contain fresh or slightly salty
water.

Movements of Ocean Water

we study the various vertical and horizontal movements of ocean water. This
chapter covers waves, tides, and ocean currents, exploring their different
types, significance, effects, and formation in a detailed manner.

The ocean water is never still; it is constantly in motion. If we observe the world
map, we see that all five oceans—Pacific, Atlantic, Indian, Arctic, and Antarctic
—are interconnected. While these names are used for educational purposes, in
reality, Earth's oceans together form a single, vast water body covering about
70% of the planet’s surface.

The movement of ocean water occurs in two primary ways: horizontal motion
and vertical motion. Horizontal motion includes ocean currents and waves,
which move parallel to the ground in a particular direction. Vertical motion
refers to tides, which involve the rise and fall of sea levels. Tides occur due to
the gravitational attraction of the Sun and the Moon on Earth's water bodies.
Understanding these movements is crucial as they influence marine navigation,
climate patterns, and coastal ecosystems.

factors that influence the movement of ocean

water.
The first factor is temperature. The temperature of ocean water can either be
warm or cold, which results in warm currents and cold currents. This variation
in temperature is primarily due to the incoming solar energy. We also know that
temperature decreases as we move away from the equator toward the poles.
This means the equatorial region has higher temperatures, while the polar
regions have lower temperatures.

Now, understand this—when water is cold, its molecules contract, making it

denser. In contrast, when water is warm, the molecules expand and spread out,
making it less dense. Essentially, temperature affects the density of ocean
water. This means the density of ocean water is comparatively greater in polar

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areas. This variation in density leads to the formation of ocean currents and
also causes water to move up and down through the ocean layers.

A good example of this is the Gulf Stream, which carries warm water from the
equatorial region to the North Atlantic Ocean along the east coast of the United
States. Similarly, the Labrador Current, a cold current, flows from the Arctic
Ocean along the coast of Labrador toward the North Atlantic.

The second factor influencing ocean water movement is salinity. Salinity refers
to the amount of salt present in water, and ocean water is naturally saline.
Always remember that cold water is highly saline, while warm water has
comparatively lower salinity. This means that highly saline water (cold water) is
also denser, and dense water is more likely to sink. When this sinking water
pushes the water below it upwards, it creates a vertical movement. The
combination of sinking and rising of water in the same area causes ocean
currents. The third factor is wind. Wind is the single biggest factor in the
creation of surface currents. If you've ever stood at the coast facing the sea,
you may have noticed strong winds moving across the water's surface, which
causes the water to move as well. These winds blow continuously, both during
the day and night. The major global winds influencing ocean currents are
Westerlies (blow from west to east) and Trade Winds (blow from east to west).
In short, when the wind blows over the ocean's surface, it pushes the water,
creating friction between the wind and the water surface, which drives the
movement of ocean currents.

The fourth factor influencing the movement of ocean water is the Coriolis force,
which is caused by the Earth's rotation. When a rotating object collides with
another moving or stationary force, it creates a new motion. The Earth's
rotation generates two distinct oceanic movements: a clockwise rotation of
water in the Northern Hemisphere and an anti-clockwise rotation in the
Southern Hemisphere. When these currents are deflected by landmasses, they
form massive oceanic circulations known as gyres. A notable example is the
Sargasso Sea, which is unique because it is not surrounded by land but by four
ocean currents—the North Atlantic Current to the north, the Gulf Stream to the
west, the North Atlantic Equatorial Current to the south, and the Canary
Current to the east.

The fifth factor influencing the movement of ocean water is the Sun, which is
the ultimate source of energy. The heat from the Sun causes ocean water to
expand. Since the equator receives the maximum amount of solar radiation,
the ocean water near the equator is about eight centimeters higher in level due
to thermal expansion. As we move away from the equator toward the poles, the
temperature drops, creating variations in ocean water temperature and density.

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This leads to the formation of warm and cold ocean currents that continuously
replace each other, keeping the ocean in motion. The sixth factor is the
topography of the ocean floor. The ocean bed contains various geographic
features similar to land, such as mountains, volcanoes, plains, valleys, and
canyons, collectively known as deep ocean landforms. When ocean currents
move over a broad area and are suddenly forced into a confined space, they
become very strong due to the massive volume of water being compressed
through a narrow opening, generating powerful currents. Similarly, if a ridge or
underwater mountain exists, the moving water is forced upward, while if there
is a trench or ditch, the water moves downward. This sudden upward and
downward displacement of water results in the creation of ocean currents.
These are some of the key factors that influence the movement of ocean water.

A wave is a to and fro motion meaning back and forth around a reference point
when the energy is moving away from the source in the form of a disturbance.
Similarly, when you look at the waves in the ocean, they are actually the
energy and not the water, and through this energy, water particles travel. Now
the question is, what creates this energy? It is the wind that provides energy,
and that's why we say wind causes waves to travel. If you have to remember
this in a simple way, then think of it this way—there are three elements: wind,
energy, and water. The wind comes, creates energy, and this energy is in the
form of a wave, and through this energy, water particles travel. Finally, the
energy reaches the shoreline, and that's how you enjoy the beautiful
movement of seawater hitting your feet. Now I'll explain why the ocean has
waves. The first thing you need to understand is that wind pushes the water
body. When wind touches the water surface, it creates a wave, and this wave
can travel thousands of kilometers in the ocean. The second thing you need to
understand is that gravity also plays an important role. Gravity pulls the water
molecules of the ocean downward. When there is friction between wind and the
surface water, it creates a natural disturbance. That's how wave energy is
created. Now this wave has a crest—you can also call it the head portion of the
wave. Wave energy always moves in a circular motion. When water travels
because of this energy, the actual motion of the water is also circular, meaning
the water goes up and down in a circular motion. As I said, this is the crest; it is
the point on the wave where the water has the maximum upward
displacement, and this happens because of the wind. Likewise, there is
something called a trough—it is the lowest point of the water displacement,
and it exists because of gravity. So when the water rises, it forms a crest, and
when it falls, it forms a trough, and then the trough is pushed up again to
become a crest. This cycle goes on over and over again, and that's how waves
travel horizontally and keep moving in a circular motion.

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The characteristics of waves include several key concepts that define their
motion and behavior. The highest and lowest points of a wave are called the
crest and trough, respectively. The wave height is the vertical distance from the
bottom of a trough to the top of a crest. Wave amplitude is one-half of the wave
height, representing both the height between the sea level and the crest and
the depth between the sea level and the trough. The wave period refers to the
time interval between two successive wave crests or troughs as they pass a
fixed point, indicating how much time a wave takes to form the next crest or
trough. The wavelength is the horizontal distance between two consecutive
crests or troughs, which should not be confused with the wave period, as the
latter measures time while the former measures distance. Wave speed is the
rate at which a wave moves through the water, measured in knots. Wave
frequency refers to the number of waves passing a given point within one
second. A high-frequency wave has more cycles in one second, whereas a low-
frequency wave has fewer cycles. The frequency of a wave depends on the
time difference between two crests or troughs. The speed of a wave is
calculated using the equation V = F × λ, where V represents wave velocity, F
is wave frequency, and λ (lambda) is the wavelength. Since wavelength is the
distance between two crests or troughs and frequency is the number of waves
traveling per second, multiplying these two values gives the speed of the wave.

Tides
Tides are the rise and fall of sea levels, occurring once or twice a day due to
the gravitational attraction of the Sun and the Moon. The study of tides is
complex, but three major celestial bodies influence them: the Earth, the Moon,
and the Sun. Each of these bodies exerts a different gravitational pull, which
collectively creates tides in the ocean. The Earth is larger than the Moon, so the
Moon orbits around it, while the Sun, being much larger than the Earth, holds
the entire solar system in its gravitational field. Smaller celestial bodies orbit
around larger ones due to gravitational attraction.

Now, imagine the Earth with the Moon positioned above it. Both the Earth and
the Moon exert gravitational forces. On Earth, gravity keeps everything
grounded, which is why objects fall back when dropped. However, water is fluid
and moves more freely. When ocean water in a particular region is directly
beneath the Moon, it experiences a gravitational pull toward the Moon, creating
a bulge on the ocean's surface—this is a high tide. Simultaneously, on the
opposite side of the Earth, another bulge forms due to centrifugal force, which
counterbalances the Moon's gravity. This results in two tidal bulges on opposite
sides of the Earth: one due to the Moon’s gravitational force and the other due

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to centrifugal force. These bulges create high tides, while the regions
perpendicular to them experience low tides.

The Sun, being the largest celestial body, also influences tides. Its gravitational
pull can either enhance or weaken the Moon’s gravitational effect on Earth.
When the Earth, Moon, and Sun align in a straight line, the Sun reinforces the
Moon’s pull, leading to exceptionally high tides called spring tides. Conversely,
when the Moon and Sun form a right angle with the Earth, the Sun diminishes
the Moon’s gravitational pull, resulting in lower tides known as neap tides. This
interaction between gravitational forces from the Moon, Sun, and Earth
continuously drives the movement of tides across the oceans.

Tides refer to the periodic rise and fall of the sea level, occurring once or twice
a day due to the gravitational attraction of the Sun and the Moon. Tides are
classified into two main categories: one based on physical patterns such as
frequency, direction, and movement, and the other based on the relative
positions of the Sun, Moon, and Earth. Based on physical patterns, tides are
further divided into three types. The first is the semi-diurnal tide, which is the
most common type and features two high tides and two low tides each day,
both of equal height. The second type is the diurnal tide, which has only one
high tide and one low tide each day, both of equal height. The third type is the
mixed tide, which exhibits variations in height and characteristics of both
diurnal and semi-diurnal tides. Mixed tides are commonly observed along the
west coast of North America and many islands in the Pacific Ocean.

Tides are the periodic rise and fall of sea levels due to the gravitational forces
exerted by the Moon and the Sun. It occurs once or twice a day. Tides are
grouped into two categories: one based on physical patterns such as
frequency, direction, and movement, and the second based on the position of
the Sun, Moon, and Earth. Based on frequency, there are three types of tides:
Semi-Diurnal Tide, which is the most common, occurring twice a day with two
high and two low tides of the same height; Diurnal Tide, where only one high
and one low tide occur each day, both of the same height; and Mixed Tide,
which has variations in height and characteristics of both diurnal and semi-
diurnal tides, commonly found along the west coast of North America and in
many islands of the Pacific Ocean. Based on the positions of the Sun, Moon,
and Earth, there are two types of tides: Spring Tides, which occur when the
Sun, Moon, and Earth are in a straight line, enhancing the Moon's gravitational
pull and creating much higher tides. These occur twice a month, during the full
moon (Poornima) and the new moon (Amavasya). Neap Tides occur when the
Sun and the Moon are at right angles to each other, diminishing the Moon's
gravitational pull and creating lower tides. There is a seven-day interval
between spring tides and neap tides. The Moon’s position relative to the Earth
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also affects tides. When the Moon is closest to the Earth, it is called Perigee
(or Supermoon), causing unusually high tides. When the Moon is farthest, it is
called Apogee, resulting in lower tides. Similarly, Earth's orbit around the Sun
influences tides. When the Earth is closest to the Sun (on January 3rd), it is
called Perihelion, leading to high tides, especially in the Southern
Hemisphere. When the Earth is farthest from the Sun (on July 4th), it is called
Aphelion, leading to lower tides. An easy way to remember this is that "Peri" is
associated with high tides, while "Apo" is associated with low tides. The terms
Ebb and Flow describe the movement of water during tides: Ebb refers to the
outgoing phase when the water level falls, while Flow refers to the incoming
phase when the water rises again.

The importance of tides lies in the various benefits they offer to human society.
Since the position of the Moon, Earth, and Sun determines tides, modern
technology has made it easier to predict high and low tides. This predictability
provides several advantages. One of the main benefits of high tide is that it
aids navigation. During high tides, the water level rises, making it safe for large
ships to enter and leave harbors. Large ships can sail more easily in deep water
when high tide occurs, reducing the risk of getting stuck in shallow areas. Tides
also help remove pollutants and circulate nutrients in ocean waters. Estuaries,
where rivers merge with the ocean, often accumulate sediments and pollutants
from river discharge. High tides help circulate and flush out these pollutants,
keeping estuarine waters clean. Additionally, estuaries are one of the most
productive ecosystems in the world, serving as breeding areas for various
aquatic animals and plants. High tides play a role in moving floating organisms
from estuaries to deeper waters, contributing to biodiversity. Another major
advantage of tides is their use in generating electrical power. Tidal energy is
classified as a renewable energy resource, and it is harnessed through
underwater turbines that are moved by water currents. These turbines activate
generators that produce electricity. Countries like South Korea, the United
Kingdom, Canada, France, Russia, and China have some of the world's biggest
tidal power plants. In India, despite having a long coastline suitable for tidal
energy production, setting up tidal power plants is an expensive undertaking.
Currently, tidal energy is harnessed in three locations in India: the Gulf of
Khambhat, the Gulf of Kutch, and the Gangetic Delta in Sundarbans.

now we will go to the next

topic ocean currents now here it says

ocean currents are like river flows in

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oceans the reason it's called a river

flow because ocean currents are

continuous and directed movements of

ocean water if you look at the ocean the

water is never still it keeps moving

towards one direction

that's why ocean currents are referred

to as a river flow now we will see what

are the forces that influences the ocean

currents to flow I've made a separate

video on it I want you to watch that and

it will tell you what you need to know I

have put the link of that video in the

description please have a look at it we

will now go to the next topic types of

ocean currents now they have been

classified into two categories surface

current and deep ocean currents the

upper 400-meter of the ocean falls under

the category of surface currents and it

constitutes about 10 percent of all the

water in the ocean

usually these surface currents are moved

by the events and they are also exposed

to these sun rays therefore they also

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get warm quickly and expand generally it

is the equator that receives maximum

amount of sun rays

therefore the water at the equator also

warms up and expand due to which

currents develop and the warm water at

the equator flows towards the poles and

cool water at the poles flow towards the

equator

when it comes to deep water currents

they make up the other 90% of the ocean

water these are water movement patterns

which are below this ocean surface and

do not have any direct influence of the

wind now the question would be how deep

currents are formed and the answer is it

is the variation in the density of sea

water in terms of temperature and

salinity and if you are wondering how

does temperature and salinity creates

current then I suggest that you watch

the video factors affecting the movement

of ocean water in that video the first

two points talk about temperature and

salinity so watch that video again and

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you will get it the link of that video

is there in the description so this was

about ocean currents based on depth the

ocean currents are also classified based

on temperature you must have heard about

cold currents in warmed currents this

picture over here the blue arrows

represent cold ocean current and the red

ones represent warm ocean current I

think this picture is self-explanatory I

don't need to tell you much about it you

can see the blue arrows that is the cold

currents they bring cold water into warm

water areas one thing that you will

notice most of the cold ocean currents

they are usually found on the west side

of the continents especially in the

lower and middle latitude and if you go

to higher latitudes you'll find the cold

currents on the eastern side of the

continent that the question is why is it

like this and the answer to this

question lies in this picture

you must be aware of the westerlies and

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easterly straight Vin's

the westerlies flow from west to east

and easterlies flow from east to west in

tropical region the Tradewinds flow from

east to west with these vents the upper

water layer of the eastern part of ocean

also moved towards west the upper layer

of the water is relatively cold in

nature that's why the western coast of

continents has cold currents when it

comes to warm currents they mostly

originate at the equator and they move

towards cold water areas that is towards

the poles they are usually observed on

the east coast of continents in the low

and middle latitudes again if you look

at the westerly and

easterly

picture you'll see that the easterlies

move from east to west right now look at

this picture as I said warm ocean

currents are generated at the equator

and at the equator we have easterlies

the vents move from east to west so if

the surface water has to move because of

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the easterly trade winds they will move

towards the western side while doing so

most of the warm currents flow along the

edges of the continent that will be the

eastern coast of the continent so you

see how warm currents are usually found

on the eastern coast of continent in low

and middle latitudes and if you see the

higher latitudes here we will have to

look at in northern hemisphere because

the southern hemisphere in high latitude

do not have much of landmass when

compared to northern hemisphere in

northern hemisphere you will see at most

places the warm currents are still on

the eastern side of the continents

however at few places he will find warm

currents to be on the western side and

the reason behind that is when the warm

current makes it way towards the pool

area you will see that at most places

the edges of landmass are interlocked

because of this interlocking the warm

current circulates and forms gyres and

that saw at some places you will find

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the warm current to be on the western

side of the continent in high latitudes

just to be clear we have covered this

topic types of ocean currents one is

based on the depth and the other one is

based on temperature now we go to the

next topic major ocean currents so

Moomins back we read about different

types of ocean currents with respect to

their depth and temperature and I also

showed your picture with those red and

blue color arrows that represent warm

and cold ocean currents there are plenty

of places on the map that shows warm and

cold currents however within these

currents there are some major ocean

currents and that's what we are going to

look at in this topic now quickly I need

to tell you this ocean currents and it's

pattern is influenced by two major

reason one is the prevailing winds as we

have seen before that the events are

responsible for moving the surface water

of the ocean and then comes Coriolis

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force few minutes back I recommended a

video

in that I have covered how winds and

Coriolis force affect the movement of

ocean water so just watch that video you

will understand these points better

anyhow as I was saying that the major

ocean currents are influenced by the

pressure exerted by the prevailing winds

and Coriolis force by watching that

video I'm assuming you must have now

understood how so this part is covered

however it's written over here that the

oceanic circulation pattern roughly

corresponds to the Earth's atmospheric

circulation pattern now what does this

mean when you hear the word atmospheric

circulation you need to understand that

it is the large-scale movement of air we

are talking about like Hadley cell

Ferrel cell subtropical high subpolar

low I also have a separate video on this

where I have explained all these things

so if you are interested please watch

that anyhow it is the wind that moves

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the ocean current from one place to

another so naturally the oceanic

circulation pattern has a close

similarity to the Earth's atmospheric

circulation pattern so basically if you

want to understand this topic in the

best possible way keep these three

pictures side by side understand defend

and the atmospheric pattern and then

connected with the ocean currents you

will find close similarities once you

have these three pictures side by side

watch these two videos which I've told

you moments back the video on your left

will tell you all the factors that

affect the movement of ocean water

because once you understand the

important factors and then the video on

your right will tell you about the

atmospheric circulation pattern now

these two videos along with these three

pictures will make you understanding

about ocean currents damn easy if you

read these lines this is basically the

summary of what you will understand if

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you do what I have asked you to do and

look the point here is that you don't

have to go so much technical about all

of this as long as you don't plan to

pursue your further studies in geography

I am assuming many of you want to know

about this because you're preparing for

some competitive exam or maybe some

school exam so keep all these facts in

your mind as well as these three

pictures along with two videos that have

asked you to watch you do all of this

you'll get it

now let's finish the last topic of this

chapter Effects of ocean currents in

this very chapter if you go back we read

about this topic called importance of

nights just go back into this video you

will recollect that I have covered three

major points as to how the tides are

important to the human society but in

this topic we are talking about the

effects of ocean currents look the basic

difference between a tide and a current

is that it tide is the rise and fall of

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ocean water and we know how the rise and

fall of the ocean water occur it is

because of the gravitational attraction

of the moon and the Sun right I hope you

remember that it is the tide that

creates a current in the ocean so

basically current is a natural flow of

water it is generated due to tide

temperature wind salinity etc etc you

see there is a difference so please

understand this difference all right now

when we look at the effects of ocean

currents the only thing that should come

to your mind is the mixing of warm and

cold ocean currents for reference always

keep this picture in your mind you must

be familiar with Plankton's right these

are living organisms which are made up

of both tiny plants and tiny animals

that live in large bodies of water since

they are living beings they need oxygen

therefore the mixing of warm and cold

ocean currents creates a perfect

temperature that helps to replenish the

oxygen and growth of plankton another

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well-known fact is that wherever warm

and cold ocean currents meet those

places are considered to be the best

fishing grounds of the world and the

reason is very simple again the

temperature at these places are exactly

right and suitable for phytoplankton

which is the key source of nutrition in

marine food chain so if we were to see

this picture and find out places that

are the best fishing ground then we need

to look at places where warm and cold

ocean currents meet these are some

highlighted areas now I'm sure many of

you must be having this question how do

these places exist in other words how

does golden warm ocean currents meet

well the answer to that has already been

discussed just go back to the topic

types of ocean currents

and see the video again where I talk

about the classification of ocean

currents based on temperature

later on I make at that topic and upload

it as a separate video for more

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convenience meanwhile just go back and

watch it again I hope that isn't much of

a problem for you the last point that I

want to say before we end this chapter

these places very cold in warm ocean

currents meet here you will find fog

because the air above warm ocean

currents is warm and the air above cold

ocean currents is school when they meet

condensation of water vapor occur and

results in fog with this

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