UNIT 2.

STRUCTURE OF THE
EARTH
Objectives
 Discuss Outer layers like:
 Atmosphere
 Hydrosphere
 Biosphere
 Describe all inner layers like inner core, outer core, sial, sima
and mantle.
 Analyze components of all layers of earth.
 2.1.External Earth Layers
The outer layers are:
 Atmosphere
Hydrosphere
Biosphere
2.1.1. Atmosphere
• The atmosphere is the envelope of gases surrounding the earth. It
contains the gases that support all forms of life on earth. This
envelope of air is dense at the sea level. It thins out with increase in
altitude.
• Atmosphere is the layer of gases surrounding the earth.
• It is composed different gases.
• It is about 360 km thickness.
 Composition of Atmosphere
Atmosphere composes:
 Gases exist as mixtures.
1. Nitrogen (78%)
2. Oxygen (21%)
3. Other gases (1%), Argon, Carbon dioxide, Helium, Methane etc.
 Dust particles. These are dust particles from the ground.
 Smoke particles
 Ash Particles
 Water Vopour ( Moistures)
Cont..
The structure of the atmosphere

• The atmosphere is a mixture of various gases

surrounding the earth. It provides all gases that are
essential for sustaining all life forms on the earth. Based
on temperature variation, the atmosphere is made up of
four layers: the troposphere, the stratosphere, the
mesosphere and the thermosphere.
Layers of Atmosphere
• Troposphere. This is the lowest layer of atmosphere.
• It is up to 15 km depth.
• It comprises majority of water Vopour in the atmosphere.
• It is where all dust particles, ash and smokes are concentrated.
Cont...
Atmosphere
Cont..
• Climatically, the troposphere is the most important because all
the elements of weather and weather phenomena occur in this
layer (e.g. evaporation, condensation, and precipitation of
different forms like fog, cloud, dew, frost, rainfall, snowfall,
thunder, lightning, atmosphere storms, etc.). This layer contains
about 75% of gaseous mass of the atmosphere, most of water
vapour, aerosols and pollutants.
Cont...
It is characterized by the following:
• It is the lowest layer of the atmosphere.
• The upper limit of the troposphere is called the tropopause.
• The temperature decreases with altitude at the rate of 6.5°C per
km or 3.6°F/1000ft.
• The atmospheric pressure decreases also with altitude and
reaches to 100 millibars and 250 millibars over the equator and
poles respectively at tropopause.
• It lies 15km above the sea level.
 Cont..
 All weather phenomena occur in this layer. These are
evaporation, condensation and precipitation. Condensation is
the conversion of Vopour or gas into a liquid of different forms.
Precipitation is water that falls to the ground as rainfall, snow
or hail.
 The height of tropopause is 17 km over Equator and 9 to 10 km over
the poles.
Stratosphere:

• The stratosphere is the layer which is extending from 16

to 50 km above the sea level.
It is characterized by the following:
• There is increase of temperature due to absorption of
ultraviolet solar radiation by ozone layer and lesser
density of air.
• There is nearly absence of weather phenomena
because of dry air and rare occurrence of clouds.
 Cont..
• The lower portion of the stratosphere having maximum
concentration of ozone is called ozonosphere, which is confined
between the heights of 15 to 35 km from sea level. Depletion of
ozone would result in the rise of temperature of the ground surface
and lower atmosphere. The main causes of ozone destruction are
halogenated gases called chlorofluorocarbons (CFCs: chlorine,
fluorine and carbon). This results to global warming, acid rain,
melting of continental glaciers and rise in sea level, skin cancer,
poisonous smoke, decrease in photosynthesis, ecological disaster
and ecosystem instability.
• The upper limit of the stratosphere is known as stratopause.
 Mesosphere

• The mesosphere extends between 50 km and 80 km.

• Temperature decreases as height increases. In fact, the rise of
temperature with increasing height in the stratosphere stops at
the stratopause.
• At the uppermost limit of the mesosphere (80 km), the
temperature drops at
• -80° C and may go down as low as - 100° C to -133° Celsius at
mesopause.
• This layer is characterized by very low air pressure ranging
between 1.0 millibars at 50 km altitude representing stratopause,
and 0.01 millibars at the mesopause (between 90 and 100 km).
Thermosphere

• It extends from 80 km to 360 km. It is composed of Ionosphere and

Exosphere.
• Its second name is The ionosphere.
• thermosphere is a layer of Earth's atmosphere that is directly above the
mesosphere and below the exosphere. It extends from about 80 km to
between 360-800 km above Earth's surface.
• It is very hot layer
• Temperatures rise as the altitude increases because the solar
radiation heats upper parts of thermosphere.
Cont...
The boundary between the thermosphere and the exosphere above
it is called the thermopause. At the bottom of the thermosphere is
the mesopause, the boundary between the thermosphere and the
mesosphere below.
Although the thermosphere is considered part of Earth's
atmosphere, the air density is so low in this layer that most of the
thermosphere is what we normally think of as outer space. In fact,
the most common definition says that space begins at an altitude of
100 km (62 miles), slightly above the mesopause at the bottom of
the thermosphere.
 Significances of Atmosphere
• Earth’s atmosphere is a thin blanket of gases and tiny
particles: together called air. We are most aware of air
when it moves and creates wind. All living things need
some of the gases in air for life support. Without an
atmosphere, Earth would likely be just another lifeless
rock. Earth’s atmosphere, along with the abundant liquid
water at Earth’s surface, are the keys to our planet’s
unique place in the solar system. Much of what makes
Earth exceptional depends on the atmosphere. Let’s
consider some of the reasons we are lucky to have an
atmosphere.
 a) Indispensable for Life of Earth
Without the atmosphere, Earth would look a lot more like the Moon.
Atmospheric gases, especially carbon dioxide (CO 2) and oxygen
(O2), are extremely important for living organisms. How does the
atmosphere make life possible? How does life alter the atmosphere?
In photosynthesis plants use CO2 and create O2. Photosynthesis is
responsible for nearly all of the oxygen currently found in the
atmosphere. By creating oxygen and food, plants have made an
environment that is favorable for animals. In respiration, animals use
oxygen to convert sugar into food energy they can use. Plants also
go through respiration and consume some of the sugars they
produce.
 b) Crucial Part of the Water Cycle

As part of the hydrologic cycle, which was detailed in the Earth’s

Fresh Water chapter, water spends a lot of time in the atmosphere,
mostly as water vapor. All weather takes place in the atmosphere,
virtually all of it in the lower atmosphere. Weather describes what
the atmosphere is like at a specific time and place, and may
include temperature, wind, and precipitation. Weather is the
change we experience from day to day. Climate is the long-term
average of weather in a particular spot. Although the weather for a
particular winter day in Tucson, Arizona, may include snow, the
climate of Tucson is generally warm and dry.
c) Ozone Layer Makes Life Possible

• Ozone is a molecule composed of three oxygen atoms, (O3).

Ozone in the upper atmosphere absorbs high-
energy ultraviolet (UV) radiation coming from the Sun. This
protects living things on Earth’s surface from the Sun’s most
harmful rays. Without ozone for protection, only the simplest life
forms would be able to live on Earth.
 d) Moderates Earth’s Temperature
Along with the oceans, the atmosphere keeps Earth’s
temperatures within an acceptable range. Greenhouse gases trap
heat in the atmosphere so they help to moderate global
temperatures. Without an atmosphere with greenhouse gases,
Earth’s temperatures would be frigid at night and scorching during
the day. Important greenhouse gases include carbon dioxide,
methane, water vapor, and ozone.
2.1.2. Hydrosphere
Hydrosphere is the layer of water that covering the earth. It is the
total amount of water on a planet. It covers or occupies about 360
million on the earth's total surface area which is 510 million . Water
covers up to 71% on the earth’s surface It includes water on the
surface of the planet, underground, and in the air. This layer is
habitat for huge number of living organisms or aquatic life.
The salt water occupies on the earth’s surface is estimated to be
97.5% of surface water.
Fresh water is only 2.5% which small amount of them can be
accessible for human use.
Cont.…
• It is a layer composed the masses of water bodies like:
1. Oceans including Pacific, Atlantic, Indian, Southern(Ant-
arctic), Arctic Oceans.
2. Seas including Mediterranean, Red Sea, Dead sea, Baltic
sea, Okhotsk sea etc.
3. Lakes including Lake Superior and Lake victoria.
4. Rivers like River Amazon, River Nile and yellow river.
 Importance of Hydrosphere
The major importance of the hydrosphere is that water sustains
various life forms and plays an important role in ecosystems and
regulating the atmosphere.
The following are the functions of a hydrosphere.
a) Water is the most important part of living cells
Every cell in a living organism is built up of about 75% of water, hence
allowing the cell to function appropriately. Cells would not be able to
carry out normal functions and life cannot exist without water.
b) Human needs
Humans use water in many ways. Drinking water is the most obvious
use, but it is also used for domestic purposes like washing and
cleaning and in industries.
 Cont..
c) Water provides habitat
Hydrosphere provides a place for many plants and animals to live in. Many
gasses like CO2, O2, nutrients like ammonium and nitrite(NO–2) as well as other
ions are dissolved in water. The presence of these substances is essential for
life to exist in water.
d) Regulate Climate
The water’s specific heat is its unique characteristic. This indicates that water
takes a lot of time to heat up and a lot of time to cool down. It helps in
regulating temperatures on earth as they stay in a range that is acceptable for
life on earth to exist.
 Cont.
e) Water are solvents which dissolves soluble substances like rock minerals.
f) Water is a source of electricity. Water is also utilized in generating
electricity through hydropower.
g) Irrigation. Water is used for irrigation of agriculture and domestic
animals.
h) Transportation. Some water bodies like Oceans, Seas, Lakes and
even rivers are used for transportation of people and goods from one
location to another.
i) Minerals. Some water bodies are source of minerals like salts, Crude
oil, natural gas, limestone manufactured for cements and others.
j) Atmospheric moisture absorbs terrestrial heat and radiates it back to
the earth’s surface keeping lower atmosphere warm.
 3.1.3. Biosphere
Biosphere is the layer of earth where life can exists. This is the zone
where all living organisms live together. It consists the lithosphere,
lower atmosphere and hydrosphere.
The biosphere, which includes the ground and the air, is characterized as
the region of the planet where organisms live. The biosphere is defined as
the region on, above, and below the Earth’s surface where life exists.
The biosphere is a narrow zone on the surface of the earth where soil,
water, and air combine to sustain life. Life can only occur in this zone. From
fungi and bacteria to large animals, there are several different types of life.
 Cont.…
The biosphere is related to the lithosphere, hydrosphere, and
atmosphere, which are all spheres of the physical world. The
lithosphere is the Earth’s solid outer layer, which contains rocks,
sand, and soil.
The biosphere is characterized as an environment that contains all
living organisms and the products of their activities. As a result, it
plays a vital role in the conservation of ecosystems, i.e., the life of
species and their reciprocal interactions. And the biosphere is
critical for climate regulation.
Any of the main greenhouse gases, such as methane, carbon
dioxide, and nitrous oxide, are affected by the biosphere.
 Cont..
Various environmental conditions, such as favorable temperature
and moisture, are needed for organisms to live on Earth. Energy and
nutrients are also needed by the species. The biosphere of the Earth
contains all of the mineral and animal nutrients needed for life.
The components of the biosphere are categorized as biotic,
abiotic, and energy components. Abiotic components include non-
Components of Biosphere

living elements such as the lithosphere, atmosphere, and

hydrosphere, while biotic components include plants, animals,
and microorganisms.
 Cont..
Abiotic components of Biosphere
I. Lithosphere (Geosphere)
It forms the terrestrial portion of the biosphere.
It is the stiff, rocky outer layer of the Earth which is made up of the crust (the
rocks that make up the continents and the ocean floor) and the upper mantle’s
solid outer layer. These layers support life by giving shelter and sustenance
from tiny bacteria to big mammals and lofty trees.
It also stretches to a depth of almost 60 kilometers, and its lower mantle and
core are the only parts that do not support life and are not a part of the
biosphere.
 Cont..
II. Atmosphere
It is the region that contains different gases like oxygen, carbon dioxide, and other
gases.
This gaseous envelope makes it possible to see insects, birds, and other creatures soar
high or fly above 2000 meters in the sky.
With the increase in height, the concentration of oxygen level goes on decreasing,
which limits the availability of organisms in the atmosphere. The region in the
atmosphere up to which animals or other forms survive or sustain makes up the
biosphere.
Besides providing oxygen for respiration, the ozone layer of the atmosphere plays a
crucial role in protecting living forms from the sun’s harmful ultraviolet rays.
 Conti..
Hydrosphere
It forms the aquatic portion of the biosphere as all the water
components of the Earth, such as waterways, ponds, oceans, etc.,
are included in it.
However, several solid forms, such as glaciers, are also included
under the hydrosphere.
It maintains the ecosystem by temperature regulation on Earth and
supplying water to all living things.
Every component of the hydrosphere is responsible for the existence
of living forms.
 Biotic components of Biosphere
Biotic components of Biosphere
Plants: These are autotrophic organisms that manufacture their food
themselves through a process called photosynthesis. These are the
primary producers, becoming the only primary source for all living
organisms.
Animals: These are heterotrophic organisms that depend on primary
producers or other animals for their food, release energy and reserve it
for future purposes. Thus, they are known as consumers.
Microorganisms: They serve as decomposers that obtain their
nutrition through the breakdown of waste or dead and decayed bodies.
Fungi, bacteria, algae, viruses, etc., are under this category.
 Energy components of Biosphere
It is the third and most important part of the biosphere,
without which life on this planet would not have been
conceivable. All biological forms on this planet depend on it
for generation and reproduction.
Every living thing functions like a machine that transforms
one form of energy into another while also using it to do
work. Sun is the ultimate source of energy for all living
organisms in the biosphere for existence.
Biosphere boundaries and interactions between components
The boundaries of the biosphere are not fixed and can vary. The
relationships between the atmosphere, lithosphere, hydrosphere, and living
organisms are complex and interrelated.
For example, the atmosphere plays a crucial role by providing gases and
regulating the climate necessary for supporting life. The lithosphere provides
physical habitats and vital nutrients for organisms.
Similarly, the hydrosphere contributes water and aquatic ecosystems to the
biosphere. These components involve nutrient cycling, energy flow, and gas
exchange, affecting ecosystems’ distribution and functioning within the
biosphere.