UNIT THREE: THE PHYSICAL ENVIRONMENT OF THE EARTH

Unit outcomes:
Physical Environment of the World
The Earth in the Universe , Forces that Change the Surface of the Earth, Weather and
Climate , Natural Regions of the Earth , Ecosystem
Physical Environment of Africa
• Position, Size, and Shape of Africa
Geological and Relief Structure of Africa, Climate of Africa , Drainage in Africa
Natural Vegetation and Wild Animals of Africa and Soils of Africa
Physical Environment of Ethiopia
Location, Size and Shape of Ethiopia, Geological Structure and Relief of Ethiopia,
Climates of Ethiopia, Natural Vegetation, Wild Animals of Ethiopia and Soils of
Ethiopia
 The Earth in the Universe
oThe Universe is the totality of space and cosmos, in which everything is found.
All heavenly bodies, including all stars, together with the sun, comets, meteors,
planets and their satellites are found in the very vast space called the universe.
oThe universe is thought to have originated as many as 12-15 billion years ago
during a ginormous cataclysm known as the “big bang.” Matter, energy and space
came to existence with a single event called the big bang.

 Hydrogen and helium are still, however, the most abundant elements,
comprising more than 99.9% of the mass of the universe.
The birth of our solar system began as dust and gases (nebula). The nebula
contracted into a rotating disc and cooling made the nebula to condense into tiny
solid particles. Repeated collision caused the dust-size particles to change into
asteroid size bodies. Within a few million years, these bodies changed into the
planets.
A galaxy is a large group of stars. The universe contains over 100 billion galaxies.
The Milky Way is our galaxy. Within the Milky Way is our solar system.
Stars some celestial bodies that have their own heat and light. Stars are made up of
vast clouds of hydrogen and helium, gas and dust.
Planet: some celestial bodies don’t have their own heat and light. All planet revolve
around the sun. planet means wanderer
Satellite: the word satellite means a smaller companion to any thing. These satellites
revolve around their planets and follow them in their revolution around the sun.
The moon for example is a satellite of the earth.

The Sun is an ordinary star, one of billions of billions that exist in the universe. The
Sun at the center, its 10 orbiting planets, plus miscellaneous comets, meteors,
asteroids, and other materials (such as space dust) are collectively known as the
solar system.
The age of the solar system (and of Earth) is at least 4.6 billion/4600 million years.
 Planet Earth
Earth is a dense planet, as are other so-called terrestrial planets located relatively
close to the Sun: Mercury, Venus, and Mars.
The mass of these planets consists almost entirely of heavier elements such as iron,
nickel, magnesium, aluminum, and silicon.
These inner planets were formed by a selective condensing of heavier elements out
of the primordial planetary nebula (the disk of gases and other matter that slowly
rotated around the Sun during the early stages of formation of its solar system).
 Earth is the third-closest planet to the Sun.
 Earth is the only place in the universe that is definitely known to sustain life.
¶ Earth is a spherical body with a diameter of about 12,756 km. It revolves
around the Sun in an elliptical orbit, at an average distance of about 149 million
km, completing an orbit in 365.26 days, or one year. Earth also rotates on its
axis every 24 hours, or one day.
Rotation of the Earth
The spinning of the Earth around its axis is called ‘rotation’.
The axis has an angle of 23 1/2º and is perpendicular to the
plane of Earth’s orbit.
Importance of Earth Rotation
The Earth’s rotation creates the diurnal cycle of lightness and darkness,
temperature and humidity changes.
The Earth’s rotation causes tides in the oceans and seas.
Revolution of the Earth
The movement of the Earth around the Sun in a fixed path is called
a revolution. The Earth revolves from west to east, i.e., in the
anticlockwise direction. The one revolution of the Earth around the
Sun takes around one year or precisely 365.242 days.
Importance of Revolution
Revolution causes seasons.
Revolution creates perihelion and aphelion. Perihelion occurs
when the Earth is closest to the Sun. Aphelion occurs when the
Earth is far from the Sun.
Revolution has a direct influence on the varied length of day and
night time. The duration of days and nights are the same at the
equator. This is known as the equinox. The duration of days and
nights vary in the Northern and Southern hemispheres. This is
known as solstices.
 Its single moon has a diameter of about 3,474 km and a mass about 2% that of
Earth. The Moon revolves around Earth in an elliptical orbit at an average
distance of about 385,000 km, completed every 27.3 days (the lunar month).
 The Structure of the Earth
o The sphere of Earth is composed of four layers; the core, mantle, lithosphere
(crust) arranged in concentric layers like an onion.
The Earth's Crust
The crust is the outermost and thinnest layer. Because it is relatively cool, the crust
consists of hard, strong rock. Crust beneath the oceans differs from that of
continents.
 Earth’s crust has an extremely complex mineralogical composition. Oceanic
crust(sima) is between 4 and 7 kilometers thick and is composed mostly of dark,
dense basalt. In contrast, the average thickness of continental crust(sial) is about 20
to 40 kilometers, although under mountain ranges it can be as much as 70 kilometers
thick. Continents are composed primarily of light-colored, less dense granite.
 The world of people and all other living things is located in a narrow zone at
the top of the crust and the bottom of the atmosphere. Relative to its size, Earth’s
crust is about as thin as an apples skin about 0.01 percent in volume.
The Mantle
 Mantle is intermediate or the middle layer of earth lies between Mohorovic and
Gutanberg discontinuity. The mantle is a less dense region that encloses the core.
It is almost 2900 kilometers thick and makes up 80 - 84 percent of the earth’s
volume. The earth’s temperature and pressure increase with depth, these changes
cause the strength of mantle rock to vary with depth, and thus they create layering
within the mantle.
The mantle lies beneath the crust and contains almost 80% of the earth’s
volume.
The Core
 The third inner most layer, the core, is a dense, hot partly molten rock composed
mainly of iron and nickel. It is a sphere with a radius of about 3470 kilometers
 The core’s temperature is about 6200 degree Celsius , which is as hot as the sun’s
surface. The outer core is molten because of the high temperature at the center of
the core. Inner core is solid due to high pressure.
 It accounts 15% of the earths volume.

There are five discontinuities which becomes the boundary of different layers of
the earth
I. Mohorovic discontinuity; Crust - Mantle boundary
II. Guttenberg discontinuity; Mantle- Core boundary
III. Concard discontinuity; Inner – Outer crust
IV. Repetti discontinuity ; Inner- Outer mantle
V. Lehyvanahs discontinuity :Inner- Outer core
 The Geological Time Scale and Major Geological Events
The geological time scale is a record of Earth’s history, starting with Earth’s
formation about 4.6 billion years ago.
Each period of time is named based on events, fossil remains and age of rocks.
It is divided in to three sub-divisions: eras, periods and epochs.
The scheme of subdivisions is based upon:
Strong tectonic activity,
The appearance or disappearance of particular forms of life,
Extensive changes in environmental conditions.

There are four eras:

I. The Precambrian
II. The Paleozoic, whose name means ancient life
III. The Mesozoic, or middle life
IV. The Cenozoic, or recent life
 I. The Precambrian Era: 4.5 billion- 600 million years
 The Precambrian era is the longest geological time unit of Earth’s history. It
comprises 88% of the geological time scale.
 Crystalline basement complex rock is formed (metamorphic) due to high heat
and pressure.
 Geologic time with poorest fossil record.
 In Ethiopia, mountain building process takes place during Precambrian era.
II. The Paleozoic Era: 600 - 225 million years
 This is the era of first organisms (ancient life) with hard parts. Warm
shallow seas covered much of earth’s surface during the early Paleozoic era.
Because of this, most of the life forms were of marine origin (lived in oceans).
This era is characterized by denudation and penaplanation
In Ethiopia, heavy erosion takes place during Paleozoic era.
There was no significant rock formation in this era.
 III. The Mesozoic Era: 225 – 70 million years
 The era of “middle” life. At the beginning, all continents were joined as a single
land mass that we call Pangaea. It separated into two large land masses
during the Triassic period. The northern mass and southern mass, respectively,
were Laurasia and Gondwanaland.
 Reptiles were the dominant animal life form in the Jurassic period.
In Ethiopia, the advancing and retreating ocean water takes place during
mesozoic era. The sea invaded the land. In the process, the layers of sandstone and
limestone were deposited one over the other.
There are three periods:
a) Triassic period: Adigrat sand stone
b) Jurassic: Hintalo lime stone
c) Cretaceous: Upper sand stone
 IV. The Cenozoic Era: 70 million- recent
The Cenozoic era is the era of recent life.
Dinosaurs and many other life forms became extinct.
Many of the mountain ranges began to form.
The climate became cooler, and ice ages occurred.
The present-day period is the Quaternary.
We live in the Holocene epoch, which began after the last ice age. Our
species, Homo Sapiens, probably appeared about 500,000 years ago, but
became a dominant animal only about 10,000 years ago.

 In Ethiopia, the deformation of uplifted land and the formation of the

Rift Valley takes place during Cenozoic era.
 The Movement of Continents

Alfred Wegener, a German meteorologist, polar explorer and visionary, who lived
between 1880 and 1930, published a book titled The Origin of Continents and
Oceans. In his book, Wegener set forth the basic outline of his radical hypothesis
of continental drift.

Wegener suggested that once there was a single supercontinent, a huge landmass,
that he called Pangaea (pan = all, gaea = Earth). Wegener further postulated that
during the Mesozoic era, about 200 million years ago, the supercontinent
(Pangaea), which centered upon Africa, began to break apart into two. He called
them Gondwanaland (which consisted of South America, Africa, the Arabian
Peninsula, the Indian subcontinent, Australia and Antarctica) and Laurasia which
included the North America and Eurasia.
  Components of the Earths Physical Environment
 Why is Earth the only planet in our solar system to support life?
Earth is a complex planet. Of all of our solar system’s planets, Earth is unique in
that it is the only planet that supports life as we know it. The earth system can be
divided into four physical systems that work together to create our physical
environment: the atmosphere, the lithosphere, the hydrosphere, and the
biosphere.
The atmosphere is the layer of gases that surrounds the earth. This mixture of
moving gases provides the air you breathe and protects the earth from the sun’s
intense harmful radiation. The lithosphere is the surface of the planet that
forms the continents and the oceans, or the land, and in the atmosphere – form
the hydrosphere (The prefix hydro means “water”). The part of the earth in
which all the planet’s plant and animal life exists is called the biosphere. These
systems are interrelated.
So, we cannot draw strict dividing lines between them. The hydrosphere supplies
humans with water and also serves as a home to animal and plant life. The
hydrosphere affects the lithosphere when, for example, a stream flows over rock,
causing the rock to worn down. Soil can be examined as part of the lithosphere,
biosphere, or hydrosphere. As far as scientists explanation goes, no other planet in
the solar system has four physical systems. Earth’s nearest neighbours, Venus and
Mars, each have an atmosphere and a lithosphere. But because of extreme heat or
cold, these planets lack supplies of water. Without water, there is no life or
biosphere. In our solar system, only Earth has the necessary four physical systems
that work together to support life.
 oForces that change the Surface of the Earth
Geology studies of how Earth's materials, structures, processes and organisms
have changed over time.
It is concerned with features which are far beneath the earth's
surface where no one can see them.
It is obtained by inference, using clues from what can be seen and
what can be measured. These processes are divided into two major
groups: internal and external processes.
I. Internal forces
Internal forces are sometimes called endogenic forces. They
drive energy from the interior part of the earth. They form the ups
and downs on the earth's crust.
The internal processes (endogenic) include volcanic activity
and all the tectonic processes:
Folding(bending), Faulting(cracking), Earth quake(shaking),
Volcanism,
Orogenesis (mountain building), and Epeirogenesis (slow rising
and sinking of the landmass).
Folding :
Folding is one of the internal processes which occur when two forces act
towards each other from opposing sides. Due to this force, rock layers are
bent into folds.
 It is bending of rocks.
The process by which folds are formed due to compressional force is known
as folding. There are large scale and small scale folds. Large-scale folds are
found mainly along destructive plate boundaries.
Types of folding:
If the fold is upward and convex, it is called anticline.
If the fold is downward, it is called syncline

Syncline fold
Anticline.

fold( down
Syncline
Anticline.

fold)
(up fold)
Fold Mountains:
What are fold mountains? How are fold mountains formed? Name some of the
fold mountains of the world.

I. Fold Mountains are formed by crust which has been uplifted, and folded by
compressional forces. They are formed when two plates move towards each
other.
Fold Mountains are usually formed from sedimentary rocks and are usually found
along the edges of continents. This is because the thickest deposits of sedimentary
rock generally accumulated along the edges of continents.
There are two types of Fold Mountains:-
Young fold mountains (10 to 25 million years of age, example, the Atlas, Rockies
and the Himalayas)
 Old fold mountains (over 200 million years of age, example, the Cape Range, the
Urals in Russia and the Appalachians of the USA).
 Many ranges of mountains have been formed by folding. The Andes, the Rocky
mountains, the Alps, the Himalayas and the Australian Alps are some examples.
The Atlas mountains in north west Africa
 The Cape Range in South Africa were formed by folding. This process of
mountain building is called orogeny.
Faulting:
•What do we mean by the term faulting?
• What are the causes for faulting?
• Can you mention some examples of landforms created due to faulting.
Faulting takes place when tectonic pressure causes rock masses to push together or
pull apart.
Movements in the crust of the earth sometimes make cracks. These cracks are called
faults. Faulting can be caused by either lateral or vertical forces, which can be either
tensional or compressional. Tension causes a normal fault, and compression causes
a reverse fault.
o Major features formed by faulting include rift valleys and
block/Horst mountains
oThe basins occupied by the Red sea, and the great "rift valleys" of
East Africa are the results of faulting.
•A rift valley is a valley formed when two parallel faults on the surface
of the earth, sinks down.
• A rift valley is a linear shaped lowland area between highlands or
mountain ranges created by geologic rifts or faults.
Activity: What is the largest rift valley in the world?
•The largest rift valley in the world is the East African Rift Valley. It extends
from Syria to Mozambique, passing through the Red Sea, Eritrea, Ethiopia,
Kenya, Tanzania, DR Congo, Rwanda and Burundi. It is about 7,200 km, of
which 5,600 km is in Africa.
The Ethiopian Rift Valley is a part of the East African Rift Valley. It
extends from northeast to south west.
o Features found in the Rift Valley include active volcanoes, lakes,
hot springs and fumaroles.
 Block (Horst) Mountains
Block mountains are formed when land between two parallel faults is pushed
upward due to pressure from inside the earth. If there are two parallel faults, the
crustal block between them may either rise to produce a Horst (block) mountain, or
fall, to produce a rift valley.
Examples:
The Sierra Nevada mountains in North America.
The Harz Mountains in Germany.
The Afar block mountain in Ethiopia.
The Ruwenzori in Africa.
Volcanism:
Volcanism is the process by which magma; gases, water vapour, ashes and other
solid materials are forced out to the surface. when this molten rock (magma) reaches
the surface, volcanic activity takes place. When the magma emerges on to the
surface, it cools and hardens. It is then called lava.
  Magma is the molten rock when it is underground.
Magma reaches the earth’s surface through two kinds of holes. They are vents and
fissures. Magma may force its way violently through a small hole called a vent. If
lava emerges via a vent, it builds up into a volcano (cone-shaped mound), and if it
emerges via a fissure

If the magma flows to the surface through a vent, a crater is formed.

Sometimes a volcano erupts very forcefully. When this happens, the top part of
the volcano is blown away. This forms a large crater called a caldera. Water
collects in the crater or in the caldera and forms a lake. We call this a crater lake
or caldera lake. In Ethiopia there are many crater lakes such as Zuquala,
Wonchi and Dendi.
Part of the magma may not reach the earth’s surface, and when this magma cools,
solidifies and forms rocks inside the crust, features such as batholiths, lacoliths,
sills and dikes, are formed.
 A batholith is a very large mass of magma which accumulates in the
crust. It is the largest structure.
A laccolith is a mushroom shaped body of intrusive igneous rock.
Smaller than a batholith.
A dike is formed when magma solidifies in a vertical or near-
vertical crack.
A sill is formed when magma solidifies horizontally or nearly
horizontally along a bedding plane.
Types of volcanoes
oActive volcano: Erupts from time to time. Erupts periodically
Eg, Erta’li, Fentale Dubbi and Damiali. Mt Ojos del salado is the
most active volcano of the world.
oDormant volcano: (Sleep volcano) has not erupted for a long time but
may erupt again in the future. Eg Tatali & Dabbahu
oExtinct volcano: (dead volcano) has not erupted within historic time
Eg, Mt. Zuquala, Ras Dashen and Batu
Fig 2: The most important types of volcanic intrusion and extrusion features
 The most active (60%) volcanoes are found in the "Ring of Fire," a horseshoe-
shaped region that encircles the Pacific Ocean.
 Importance of volcanic eruptions: Large volcanic eruptions can also disturb
great expanses of life, forest and other ecosystems. Beyond this, volcanic eruptions;
Give us some ideas about the interior of the earth.
Provide fertile soil.
Provide hot springs (with medical value).
Generate geothermal energy.
Help in the formation and concentration of minerals.
Help in the creation of new land.
 Earthquake
 Earthquakes are sudden movements (trembling or shaking) in the earth’s crust.
They are caused by internal movements deep down inside the earth. Earthquakes
are frequently associated with faults. An earthquake is the result of the sudden
release of stored energy in the Earth's crust that creates seismic waves.
The point at which an earthquake originates is called the focus. The point on the
earth’s surface immediately above the focus is called the epicenter. As the vibrations
spin out from the centre, the damage they cause becomes less and less.
 An earthquake is caused by tectonic plates getting stuck and putting a strain on the ground.
The intensity of an earthquake is measured by an instrument called a
seismometer, and is recorded on a seismograph. It records the vibrations
produced by an earthquake.
The scale which gives the magnitude is called the Richter scale. It ranges from
0 to 9. Each number of this scale indicates a tremor that is ten times stronger than
the next lower number.
The strongest ever recorded earthquake was the Valdivia earthquake in Chile
that occurred on May 22, 1960 (9.5 on the Richter scale). >8.1 on Richter scale
results in total destruction.
 Effect of Earthquake :
•Loss of life and property
•Displacement of parts of the earth’s crust vertically or laterally.
•Landslides and deep cracks in surface rocks.
•The devastation of cities, fires and diseases.
•The rise or lowering of the sea floor.
 Earthquakes Ring in the world .
About 80% of all earthquakes occur in three regions. They are
a. Around the Pacific Ocean zone. The largest earthquake and volcano zone
lies along the edges of the Pacific Ocean. This zone is known as the Pacific
Ring of Fire.
b. Across Southern Europe and Southern Asia.
c. The west-coast areas of North and South America.
 II. External Forces
oExternal forces are the forces that act upon the earth's surface from outside.
oThese forces level the ups and downs of the earth's surface.
The external (exogenic) processes are geomorphic processes. They include
weathering, mass wasting, erosion and deposition.
They act upon the volcanic and structural landforms by modifying, roughening
and lowering them down.
Weathering
o External forces can lower the level of the land by washing it away, and this
process is called denudation. They also can raise the level of the land by
deposition.
o Denudation consists of weathering and erosion.
Weathering includes disintegration (physical weathering), which breaks rocks into
smaller pieces and decomposition (chemical weathering), which forms new
substances.
  Physical (Mechanical) Weathering
 Is when rocks are broken apart( in to pieces) by mechanical processes such as rock
fracturing, freezing and thawing, or breakage during transport by rivers or glaciers.
Its main agents (causes) are:
 The effect of temperature changes: cracked rock layer peels off and falls to the
ground due to variation in temperature, this process is called exfoliation.
 Frost action: Due to frost action, rock breaks up into pieces and these fragments
accumulate around the lower slopes of the rock. This material is called scree. Frost
action is very common in the winter season
 Action of plants and animals. As plants with in crack of rock develop their roots
may push the rock apart. Some animals burrow, and this also helps to break up rocks.

 Chemical Weathering (Decomposition)

 Chemical weathering is a process that forms new substances, and it is affected by the
minerals in the rock. Its main agents are rain action and plant and animal actions.
Exfoliation domes
o Chemical weathering is a process where minerals in a rock may be converted into
clays, oxidized or simply dissolved.

When acid water comes into contact with rock, it begins to dissolve minerals in the
rock. This process is known as carbonation.

H2O + CO2 ⇒ carbonic acid ⇒ dissolves and erodes limestone and forms caves.
Example: Sofomer Cave along the River Weiyb in Bale.
These caves contain features such as stalactites, stalagmites and pillars.
A stalactite is a limestone column that hangs down from the ceiling of the cave.
A stalagmite is a limestone column that builds upwards from the floor of the cave.
A pillar is formed when a stalactite and a stalagmite join together.

• When rain water dissolves oxygen and reacts with iron in rocks, the rocks
become rusty. Pollution in towns and cities increases chemical weathering.
  Erosion
Erosion is the action of surface processes (such as water flow or wind) that
removes soil, rock, or dissolved material from one location on the Earth's
crust and then transports it to another location where it is deposited.

 Erosion will often occur after rock has been disintegrated or altered
through weathering.

Erosion occurs when particles of rock or soil are:

washed away by a river
removed by waves of the sea
crushed under a glacier
blown away by the wind

o Erosion by Running Water

Rivers are the most important of all natural agents which help in shaping the earth’s
surface. The work of running water includes eroding, transporting and depositing
eroded material.
There are three types of running water erosion:
1 Sheet erosion: occurs when surface water moves in a wide flow and resulting in
the removal of a uniform layer of soil from the soil surface.
2 Rill erosion: occurs when surface water cuts relatively small channels.
3 Gully erosion: occurs when floods cut deep wide gorges.

Rill and sheet erosion on a cultivated land

 Gully erosion
This type of erosion is highly visible and affects soil productivity, restricts land
use, and can damage roads, fences and buildings.
 The course of a river, from its source to its mouth, can be divided into 3 stages.
The stages are upper course, middle course and lower course.
Upper Course: youthful stage; In this stage the river water is small in volume.
 vertical erosion  It flows at a very fast due to the steep gradient.

 weathering, Potholes The features found in the youthful stage of a

 head ward erosion . river are all formed by the processes of Erosion.
 v-shaped valley, Interlocking Spurs
 waterfalls, rapids gorges are formed because the river flows very fast
Middle Course: mature stage: the river valley becomes wider and larger.
 is characterized by lateral erosion, transportation and deposition which makes the
river to develop a gentle slope.
 floodplain, meanders
 river cliff
Lower Course: old stage
 transportation
 large channel,oxbowlakes, levees, large floodplain , big meanders, deltas/estuaries
 At the Old age stage the river is usually at it’s widest. The land is also at its

flattest. This means that the river has to work very hard to make its way to the sea.
The main agent at work now is Deposition.
Features of the lower course of a river
Floodplains: are broad flat areas which border with the lower course of a river and
are sometimes flooded by the river. They are covered with fertile alluvial soils
which are deposited by the river when flooding.
Levees are narrow ridges of alluvial deposits found along the bank of a river.
 They are formed as a result of flooding.
Ox-bow lakes: are crescent-moon shaped lakes created due to meanders that have
been abandoned. They are formed when meanders are cut off from the main river
channel.
Deltas: are usually triangular areas of land which are usually formed at the mouth
of rivers.
Source: Where a river begins.
Tributary: Smaller rivers/streams that join the main river.
Confluence: The point where two rivers join.
Estuary: The part of the river (mouth) which is tidal.
Mouth: Where the river enters the sea/lake.
Watershed: The area of high land that separates two basins.
Course: (channel)The route taken by a river between its source
Erosion and Deposition by Sea Waves
 Waves are formed when wind moves over the surface of the sea. This
movement of water in the sea clashes against coastal lands and picks up rock
particles and throws them into the sea as sediments. The work of the sea along the
coast includes erosion, transportation and deposition.
Features formed along the shoreline are:
Beaches
Spits
Lagoons.
Beach is a strip of land along the sea coast covered with various types of sediment.
A Spit is a narrow ridge of sand or shingle. It projects into the sea but is attached to
the land at one end.
Lagoon is an area of saltwater separated from the sea by loose sandbanks.
Wind Erosion and Deposition
Wind erosion is common in desert and semi-desert areas. Wind erosion and
deposition form different landforms such as sand dunes, barchans and loess
deposits.
Landforms associated with wind erosion
Sand dune: is a small hill of sand formed by the action of the wind.
Barchan: is a sand hill that has a crescent-moon shape.
Loess deposit: is a deposition of fertile soil in the desert by wind.

Weather and Climate

 weather refers to short-term changes in the atmosphere, climate describes what
the weather is like over a long period of time in a specific area. In most places,
weather can change from minute-to-minute, hour-to-hour, day-to-day, and
season-to-season. Climate, however, is the average of weather over time and
space.
 What is atmosphere?
The air that surrounds the earth is called the atmosphere. It is an envelope of
transparent colorless, tasteless and odorless gases found above the earth’s
surface.
 Composition of the Atmosphere: The earth’s atmosphere is a mixture of
gases, suspended dust particles and condensed moisture droplets which are
collectively known as aerosols. The gases are different in their volume

Earth’s atmosphere is composed of about 78 % nitrogen, 21% oxygen, 0.9 %

argon, and 0.1% other gases. Trace amounts of carbon dioxide, methane,
water vapor, and neon are some of the other gases that make up the remaining
0.1 percent.
 Atmosphere layers and their characters
The atmosphere is divided into five different layers, based on temperature.
1. Troposphere: The layer closest to Earth’s surface is the troposphere,
reaching from about seven and 15 kilometers from the surface.
 This is the lowest part of the atmosphere - the part we live in.
 The troposphere is thickest at the equator, and much thinner at the North
and South Poles.
 The majority of the mass of the entire atmosphere is contained in
the troposphere—between approximately 75 and 80 %.

 In this part of the atmosphere the temperature gets colder as the distance
above the earth increases, by about 6.5° C per km
Most of the water vapor in the atmosphere, along with dust and ash particles,
are found in the troposphere explaining why most of Earth’s clouds are located in
this layer.
 Temperatures in the troposphere decrease with altitude: this is due to result of
the decreasing pressure.

 The top boundary is called the tropopause, Known by (jet streams

)Turbulence as the wind blows over the Earth's surface,

2. The Stratosphere: This extends upwards from the tropopause to about 50 km.
It contains much of the ozone in the atmosphere.
 The increase in temperature with height occurs because of absorption of
ultraviolet (UV) radiation from the sun by this ozone.
 Has constant temperature. Stratopause is boundary /upper limit
3. The Mesosphere:
 The region above the stratosphere is called the mesosphere. Here the
temperature again decreases with height, reaching a minimum of about -100°C
at the "mesopause".

In fact, the coldest temperatures in the atmosphere are near the top of
the mesosphere about -90°C (-130°F). The atmosphere is thin here, but still
thick enough so that meteors will burn up as they pass through the mesosphere
creating what we see as “shooting stars.” The upper boundary of
the mesosphere is called the mesopause.
4. The Thermosphere: is located above the mesopause and reaches out to around
600 kilometers. Not much is known about the thermosphere except that
temperatures increase with altitude. Solar radiation makes the upper regions of
the thermosphere very hot, reaching temperatures as high as 2,000°C (3,600°F).
 Thermosphere is divided in to to two layers;
o The ionosphere: is a layer of electrically charged particles. Radio wave
transmitted from this layer reflected back to earth from this layer.
o The uppermost layer, that blends with what is considered to be outer space, is
the exosphere. The pull of Earth’s gravity is so small here that molecules of
gas escape into outer space.

Meaning of Weather and Climate

 Weather is the condition of the atmosphere over a short period of time.
Weather includes daily changes in precipitation, air pressure, temperature,
wind, etc. Weather refers to atmospheric conditions in a given location.

 Climate is the average of all weather conditions of an area over a long

period of time. These conditions include average temperature, air pressure,
humidity, and days of sunshine for a period of 30 years. Climate tells us what it
is usually like in the place where we live.
 Major Elements of Weather and Climate
 The major elements of weather and climate are temperature, rainfall, winds,
air pressure, clouds, humidity etc.
 Temperature
Temperature is the amount of hotness or coldness of an object.
 The sun is the primary heat source for the earth and its atmosphere.
The sun’s energy is called insolation or solar radiation, and this turns into heat
energy at the earth’s surface.
Freezing point of water = 0°C/ 32 °F
 Boiling point of water = 100°C/212 °F
 Room temperature = 20°C/72 °F
Heat Budget
Not all the energy that originates from the sun reaches the earth’s surface.
 51%_ absorbed by Earth surface
 20%_ reflected by cloud
 19%_ absorbed by Atmosphere and cloud
 6%_ reflected by atmosphere
 4%_ reflected from surface
How is energy transferred in the atmosphere?
Not all the energy that originates from the sun reaches the earth’s surface
Heat transfer takes place in three ways. These are

• Conduction: Molecule-to-molecule transfer

• Convection: Energy transferred by movement
• Advection: advection is the transport of a substance or quantity by bulk
motion of a fluid.
• Absorption: Assimilation of radiation by matter
Radiation is the transfer of energy from one body to another by means of
electromagnetic waves. Energy transmitted from the sun reaches the earth’s
surface through the process of radiation. Electromagnetic waves usually
travel through empty space.
 The sun warms the earth through radiation of electromagnetic waves.

Conduction refers to the transfer of heat through molecular contacts within

and between bodies. Molecules are always in motion.
 The process of conduction is more important in solids. Air and water are
poor conductors of heat.

Convection is the transfer of heat due to differences in density. As gas or

liquid either warms and rises or cools and falls, it creates convection currents.
Convection is the method by which heat moves through gases or liquids.
Warm air rises; cold air sinks due to convection
  Measuring and Recording Air Temperature
We measure temperature with thermometer. There are two types of thermometers:
maximum and minimum thermometers.
A maximum thermometer is a mercury-in-glass thermometer that has a
constriction near the bulb end. When the temperature of air rises, the mercury in
the thermometer expands and forces its way into the stem past this constriction.
But when the bulb cools, none of the mercury above the constriction moves back
into the bulb. The end of the mercury thread, which is the farthest from the bulb,
registers the highest temperature reached in a day.
oThe freezing point of mercury is –38.83 °C , and the boiling point is 356.73 °C
o The freezing point of Alcohol is – 130 degree Celicus

A minimum thermometer has alcohol as its liquid, and it sets a metal index.
When the temperature falls, the alcohol column drags the index towards the bulb
end.
 When the temperature rises, the alcohol column expands and runs past the
index without disturbing it. Thus, the end of the index, moves the farthest from
the bulb and gives the lowest temperature attained in a day. The standard
thermometer for environmental measurements needs only to cover the range
between -30°C to 50 °C .
o Maximum and minimum thermometers are kept in a box-like shelter which
is known as a Stevenson screen.
Daily march of temperature or the diurnal range.
The difference between the highest and the lowest temperatures during 24 hours
Daily average (mean) temperature:
Is obtained by adding the maximum and minimum temperatures of a day and
dividing the sum by two.
Annual march of temperature / annual range
The change of temperature from month to month within a year
 the difference between temperatures of the hottest and coldest months in a year.
  Monthly average (mean) temperature is calculated by adding all daily
averages and dividing the sum by the number of days of the month/30days /.
 Annual average is obtained by adding the average monthly temperatures and
dividing the sum by 12.
Act;1 Study the climate data for a station ‘X’ and answer the questions that follow.
(a) Calculate the annual mean(average) temperature for the station.
(b) Determine the rainfall range.
(c) Identify the season of heaviest rainfall.
(d) Find the temperature mode and median.
(e) Comment on the relationship between temperature and rainfall for the station.
Month J F M A M J J A S O N D

Temp. (°C ) 28.3 27.5 28.5 29 26.7 26 26 25 24 26 27 28

Rainfall (mm) 380 330 240 175 170 5 2.5 2.2 17 50 210 230
Rainfall
What is rainfall?
 Rainfall is liquid precipitation. Any moisture that falls from the clouds towards
the earth’s surface is called precipitation. Precipitation may occur in the form
of rain, snow, hail, sleet and drizzle.
 Precipitation is part of the water cycle or hydrological cycle. The water cycle
begins as water is changed from liquid to vapor by evaporation and transpiration
of water vapor.
 Once water vapor is formed, it expands and cools. Then, condensation
occurs, forming clouds, and the water falls as snow, sleet or rainfall. The whole
process is powered by solar energy and is repeated continuously. This whole
process is called the hydrological cycle.
Evaporation is the process by which liquid water is converted into gases.
 Transpiration is the transfer and change of water from plants to water vapour
in the air.
 Evapotranspiration is the combined loss of water through the process of
evaporation and transpiration.
 Condensation is the process by which vapour becomes liquid.
 Sublimation is the process in which ice changes into water vapor without first
becoming a liquid, and vice versa.
Fig; Water exists in three forms
  Water is a unique substance, because it can exist in three states as liquid, solid
and gas) in the atmosphere.
 Types of rainfall
Rain is given three different names according to the different ways in which
moisture is forced to rise. They are:
I. Convectional rainfall
II. Orographic or relief rainfall
III. Cyclonic rainfall

I. Convectional rainfall: When the ground surface is heated by the sun, the
air above it is warmed up. At high altitudes, the water vapour cools,
condenses to form clouds and falls as rain.
 This type of rainfall is common in humid areas where temperature is high
throughout the year.
II. Orographic (relief) rainfall: occurs when moist air is forced to rise over
mountains. As it rises, it cools, then condenses and falls as rain. Almost all
orographic rainfall falls on the windward side of mountains.
III. Cyclonic or Frontal rainfall when two air masses (warm and cold) meet,
they do not mix freely with each other.
 The warmer and less dense air is forced to rise over the colder and heavier
air. As the warmer air rises, it cools and condenses. Then clouds form and
rain falls. The place where warm air and cold air meet is called a front.
 Frontal rainfall is very common in the middle and high latitudes (60 north
and south from the equator)
 Measuring and Recording Rainfall
 Rainfall is measured using an instrument called rain gauge. A rain gauge
consists of a wide-mouthed funnel placed over a cylindrical container.
The amount of rainfall is measured in millimeters and is recorded.
Total annual rainfall is the sum of rainfall recorded in total months in a year(12)

 Rainfall mode; the number that occurs most often in a data set.
 The median is the middle number in a set of values when those values are
arranged from smallest to largest. When a set has an even number of values,
the median is the mean of the two middle values
Activity 2:

Month J F M A M J J A S O N D
T(°C) 30 30 30 31 32 38 37 37 35 34 31 30
Rf (mm) 10 20 26 15 8 0 0 0 12 18 15 10

• Determine the annual rainfall.

• Calculate the mean annual temperature.
• find the rainfall mode and median
•What type of climate does station X experience? Give reasons
• Suggest the hemisphere in which station X is located.
Activity
1. By referring to the above Table ,
a. Calculate annual range of temperature.
b. Calculate annual average (mean) temperature.
2. When do the maximum and minimum temperatures of the month occur in
Ethiopia? Why?
 Air Pressure

 The weight of air exerts pressure on the surface of the earth. We call this
atmospheric pressure. Air expands in summer due to high temperature and in
winter it shrinks due to low temperature.

 Atmospheric pressure is vary through place and time.

 Pressure is measured by a mercury barometer.
 Normal pressure, at sea level, is about 760 mm/1013 mb.
 The distribution of pressure over the earth’s surface depends on
A. The altitude of places above sea level
B. Temperature.

 Pressure decreases with an increase in altitude. This explains why air

pressure is highest at sea level and decreases with increasing altitude. High
temperature makes air expand, so that it has a lower density and pressure.
 The distribution of air pressure over the globe is known as the horizontal
distribution of pressure.
 Lines connecting all places that have the same pressure are called isobars.
Global Pressure Belts:
1. Equatorial low pressure belt (Doldrums):
 Located from 5 °C North to 5° C South.
 There is tremendous heat, and thus warm air, creating low pressure. Also,
the centrifugal force is very high at the equator, because the earth’s velocity of
rotation is high. Hence, the air masses tend to be thrown outwards, resulting in
low pressure. Wind speed is low,
 Due to calm air movements in this pressure belt, is called Doldrums.
 The Inter tropical Convergence Zone (ITCZ )known by sailors as
the doldrums or the calms because of its monotonous windless weather, is the
area where the northeast and the southeast trade winds converge.
2. Tropical high pressure belt (Horse Latitude): (30 ° to 35 °) North and South.
oTemperature is usually high.
o pressure is high, because pressure depends on the rotation and movement of air
(as winds from the Doldrums rise up and accumulate here. Also winds from the
sub-polar low pressure belt accumulate here).
oThe horse latitudes were named by the crews of sailing ships, who sometimes
threw horses overboard to conserve water when their ships were becalmed in the high-
pressure belts.
3. Sub-polar low pressure belt:
Located from 60° to 65°, North and South.
Here the low pressure is created because of intense high pressure at the poles.
4. Polar Highs
Located near the north and south poles.
The polar zones have permanent centers of high pressure known as polar highs.
 At poles high pressure regions are formed because temperature remains low for
whole of the year.
 Wind
o The wind is moving air that is caused due to the differences in air pressure within
our atmosphere. Wind force (speed) and wind direction are affected by:-
 Pressure gradient
 Frictional force: force that causes movement of wind to slow down.
 Coriolis force: the force which affects the direction of movements of winds
formed due to Earths rotation deflects wind and air current

 The difference in distance between Isobars is called the pressure gradient.

• If the isobars are closely spaced, we can expect the pressure gradient force to be
great, and wind speed to be high.
• In areas where the isobars are spaced widely apart the pressure gradient is low
and light winds normally exist.
• High speed winds develop in areas where isobars are closer.
 Cyclones are atmospheric disturbances which involve a closed circulation
about a low-pressure center. They move inward, anticlockwise, in the Northern
Hemisphere and clockwise in the Southern Hemisphere.
o Cyclones are commonly known as lows or low pressure areas.
Anti-cyclones are vast areas of high pressure which have a diverging system
of surface winds. The winds in anti-cyclones blow outward in the anti-clockwise
direction in the Southern Hemisphere and in the clockwise direction in the
Northern Hemisphere.
o Anticyclones are commonly called highs or high pressure areas.
 Wind speed is often measured with anemometer.
 Wind Direction is measured by an instrument called wind vane.
Types of Winds
There are three types of surface winds. They are:
1. Planetary 2. Monsoon 3. Local winds.
1. Planetary: Planetary winds blow over large areas of the earth’s surface.
The most common planetary winds are
• Trade winds
• Westerlies: These winds blow from Sub tropical high pressure belt toward
Sub polar low pressure belt.
• Polar easterlies: the Polar easterlies are cold, dry permanent winds that blow
from north-east to south-west direction in the Northern Hemisphere and south-
east to the north-west in the Southern Hemisphere.
o Easterlies blow from the high-pressure polar areas of the sub polar lows.
• Trade Winds
Trade winds are also known as tropical easterlies and blow from the right in the
Northern hemisphere and to the left in the Southern hemisphere due to Coriolis
effect.
oThey start blowing from the sub-tropical high-pressure areas towards the
equatorial low-pressure belt. In the Northern hemisphere, they blow as
northeastern trades, and in the Southern hemisphere, they blow as southeastern
trades.
2. Monsoon winds:
•Monsoon winds are classified as periodic/ seasonal winds as they change their
direction periodically.
Monsoon winds are very common in South and South East Asia. Seasonal
changes in the direction of these winds are caused by the unequal heating of land
and water surfaces. The direction of monsoon winds changes between summer and
winter.
3. Local winds:
• They affect only limited areas and blow for a short period of time.
•The local differences in temperature and pressure produce local winds. Such
winds are limited to the lowest levels of the troposphere.
 The main local winds are:
A. Land and sea breezes
B. Mountain and valley breezes
A. Land and sea breezes :these winds are common along coastal areas.
These winds change their directions daily and affect very small areas. During the
daytime, temperature on the land is higher than on the water/sea. So low pressure is
formed on the land, while it is relatively high on the sea.
 Wind blows from the sea towards the land. This is known as a sea breeze. At
night the land is colder than the sea. So low pressure develops over the sea.
The wind blows from land towards the sea. This is known as a land breeze.
B. Mountain and valley breezes: Mountain and valley breezes arise from
contrasts in temperature between a valley floor and mountain slopes.
 During the day the air at the bottom of the valley becomes warmer. As a result it
expands and rises along the mountain slopes. This is known as a valley breeze.
 At night the wind over the slope of the mountain becomes cool. Then this cooler
and heavier mountain air slides down slopes towards the valley. This is called a
mountain breeze.

Clouds
What are clouds? How are clouds formed? What are the major types of
clouds?
A cloud is a dense concentration of very fine invisible water droplets, sleet or ice
crystals. Clouds are formed by the condensation of water vapour below the dew
point in the atmosphere.
  Controls of Weather and Climate
Major controls of weather and climate
A. Latitude
B. Altitude
C. distance from the sea
D. cloud cover
E. ocean current
F. planetary winds and pressure.

A. Latitude:

o latitude is the most important factor determining the strength of heat reaching
the earth’s surface.
o When the sun’s rays are vertical (at a right angle) to the surface, the amount of
heat received is the greatest. But when sun’s rays are slanting (oblique) the heat’s
strength decreases.
 The sun is overhead at noon for six months between the equator and the
Tropic of Cancer.
 it is overhead for another six months between the equator and the Tropic of
Capricorn.
 The sun is directly overhead at the Tropic of Cancer on June 21 (the June
solstice)

 The sun is directly overhead at the Tropic of Capricorn on December 21

(the December solstice).
 At March and September equinoxes, the sun is directly overhead at the
equator.
 At times between solstices and equinoxes, the sun is overhead in tropical

areas in the zone between the Tropic of Cancer and the Tropic of Capricorn.

 The sun is never overhead outside of the tropics. The sun is closer to overhead
in the middle and high latitudes on the day of their hemisphere’s summer solstice.
 B. Altitude
 Air temperature decreases with increasing altitude. The normal decrease
of temperature with height is 6.4° C per 1000 m. This is known as the normal
lapse rate.
 The normal lapse rate is the average rate or proportion at which temperature
changes per unit of altitudinal change.
Activity: What would be the temperature be at the top of mountain Ras
Dashen assuming that the temperature at sea level is 30 ° C?
C. Distance from the Sea
o Land heats more quickly than water. But it loses its heat quicker than water.
Therefore coastal regions are cooler than inland regions.
o In winter in mid-latitudes, the ocean surface is much warmer than land
areas. So, onshore wind brings heat to coastal lands.
o During the summer, coastal areas remain much cooler than inland sites.

D. Cloud Cover
o Cloud reduces the amount of solar radiation reaching the earth’s surface and
the amount of radiation reflected from the earth’s surface. When there are no
clouds both types of radiation will be at a maximum level.
 Cirrostratus

-6000m
Cumulonimbus

Altostratus

-4000m
Altocumulus

Cumulus

Stratocumulus
Nimbostratus -2000m
Stratus
E. Ocean Current
o Ocean current is the horizontal movement of ocean waters caused by winds and
differences in temperature. The effect of ocean currents on temperatures depends
upon whether the current is cold or warm. The water at the equator is warmer and
less dense than that in polar areas.
o Convection currents in the oceans result in a pole ward flow of warm, light,
surface water.
o Ocean currents are the source of temperature regulation on the earth.
o A warm ocean current makes the weather of the nearby regions to go up in
temperature, whereas cold ocean currents reduce the surrounding temperature.
o For instance, the European coasts get warmth from the ocean current of the
Mexican Gulf stream, and southwestern Africa’s Namib Desert is cooled by
the Benguela current off the continent’s western coast
  Major Natural Regions of the Earth

The earth can be divided into three major temperature zones. These are:
I. Tropical (hot) zone.
II. Temperate zone.
III. Frigid (cold) zone.
I. Tropical (Hot) Zone
 The tropical or hot zone is the zone between the Tropic of Cancer (23½ ° N)
and Tropic of Capricorn (23½ ° S).
The tropical zone is characterized by high temperature throughout the year.
Along the equator there is dense forest
Agriculture and mining are the major economic activities of the zone.
The tropical zone is divided into four sub-regions. These are:
The equatorial rainforest region
The savanna grassland region
The desert region
The tropical monsoon land.
  The Equatorial Rainforest Region

They are found in the lowland areas within 6 ° north and south of the equator. The
main areas in the world include;
o The Amazon Basin
o The Congo Basin
o Southern Malaysia and some Indonesian islands
The equatorial rainforest region does not form a continuous belt around the earth.
The Amazon Basin is the most extensive area.
Climate:
• Equatorial rainforest region has uniformly high temperature and heavy rainfall
throughout the year. Rainfall in this region is mainly of a convectional type
• The total annual rainfall is very high, usually between 1500 mm and 2500 mm.
• All months have rainfall with a small variation in amount.
Natural Vegetation;
oThe region has dense, tall, broad-leafed and evergreen trees.
oplants growth continuous. Known by most luxuriant (dense) type of natural
vegetation in the world.
oMost of the trees are hardwood, such as rosewood, ebony, and mahogany,
which are valuable for making durable furniture.
o Trees are closely spaced and interlaced with climbing vines called lianas.

Wild Animals;
oThe Equatorial rainforest is inhabited by varieties of animals, such as
insects, birds, reptiles, mammals. Most mammals are arboreal/tree
climbing such as apes, monkeys, bats, squirrels, etc.
oWater body animals, such as crocodiles, alligators, hippopotamuses,
fish, etc, are also available.
Human Activities;
The human activities found in equatorial rainforests include;
 primitive hunting and gathering,
shifting cultivation; due to nature of soil( leaching results laterite soil.)
plantation agriculture: large scale production of one or two crops for sale.
o cacao production from Ghana.
o Rubber plantation crops in Malaysia, Indonesia and Congo.
 mining. The equatorial rainforest region is a source of useful minerals.
oBauxite is found in Ghana, Guyana and Venezuela.
oPetroleum is found in Nigeria, Venezuela, and Indonesia.
oIron ore is found in Liberia.
 Tropical Deserts
oDeserts are almost barren lands.
oThe tropical hot deserts are located between 15° to 30° north and south latitudes
of the equator.
oThe largest hot desert is the Sahara desert. There are also other important
deserts such as the Kalahari, Atacama, Colorado, Arabia, Thar and Australian
deserts.
 How deserts are formed?
oDeserts are formed due to their:
in the trade-wind belt
on the leeward side of high mountains
in the interior of continents
along cool ocean currents
•Deserts are located on the western margins of continents, except for the Sahara Desert,
which is in North Africa and extends to the northeastern coast of the African continent.
 Arabian
Colorado Thar
Sahra

Atacama Calahari
and Namib
Australian
desert
Climate;
• The main characteristics of desert is that the climate is hot throughout the year,
and there is very low and unreliable rainfall (not more than 250 mm per year).
• Temperature ranges from 25° C to 40° C or above during the daytime, and they
can fall even below 0° C during the night, due to the absence of clouds. The
winds are warm and dry. So deserts have hot day and hot night
Vegetation;
The climate of the hot desert is not favorable for plant growth. However, Plants
with long roots, few or no leaves, hard bark and an oily leaf surface; these
features help the plants to reduce the loss of water by evapotranspiration.
o These are called xerophytes. Xerophytes are woody and thorny plants, grasses
and herbs, for example cacti.
Animal life;
o Animals such as gazelle, hare, fox, snakes, lizards, etc are commonly available
in the desert region. For the desert people camel is their best companion
Human Activities;
o The major economic activities are pastoralism, crop cultivation and mining.
o Small-scale crop cultivation is possible along wadis (small streams) and in the
oases; dates, vegetables, fruits and cereals are grown. In areas where the deserts
are crossed by rivers, irrigation on a large scale is possible. The waters of the Nile,
Tigris-Euphrates and Indus have made possible the cultivation of crops in desert
areas.
o Desert people practice nomadic way of life.
o Most deserts are important sources of minerals.
•The Middle East alone accounts for about 60% of the world’s total oil reserve.
• nitrates and copper in the Atacama
• gold in the Australia Desert, diamond in the Kalahari
• natural gas in the Sahara Desert and the Middle East,
• phosphate and iron ore in the northwest Sahara Desert.
  Vertical Distribution of Climate in Ethiopia
 Ethiopia lies within the tropics (3° N to 15° N latitude).
 It lies in a zone of maximum insolation where overhead sun twice a year.
The traditional classification of climatic zones of Ethiopia is divided into five:
1 Bereha (hot arid): found below 500 m a.s.l., where the average annual
temperature range is between 30° C and 40° C or higher.
2 Kola (warm to hot semiarid): It is a climate of hot lands with altitudinal
ranges of 500 - 1,500 m a.s.l. Average temperature is between 20° C – 30° C.
3 Weina dega (warm to cool semi-humid): This is a zone which covers the
temperate highlands that fall in altitudinal ranges of 1,500 – 2,300 m a.s.l. Its
average annual temperatures are between 15° C and 20° C.
4 Dega (cool to cold humid): This describes the cool temperate highlands with
an altitude ranging from 2,300 – 3,300 m a.s.l. and average temp b/n 10° C to 15°C.
5 Wurch (cold moist temperature): It coincides with the Afro-alpine areas on
the highest areas of the plateaus. The lower limit of the wurch zone
 II. Temperate Zone
o The temperate zone is located between 23° ½, and 66° ½, both north and south
of the equator. The temperate zone is the transitional zone between the tropical
zone and the frigid zone.
o It is also known as a mid-latitude region.
Climate;
oTemperate regions usually have four distinct seasons. They are summer, winter,
autumn and spring. Weather changes are observed in each season. Precipitation
ranges from 750 mm to 1500 mm. Temperature ranges from below freezing point
during the winter, to 30° C or more during the warmest days of summer.
There are important factors that bring about frequent weather changes in the
temperate zone. These are:
o Convergence of tropical and polar air masses: This results in cyclonic storms
and fronts.
o Angle of the sun: The sun is never overhead in the temperate zones.Therefore it
does not heat the earth very much.
o Length of day: There is a big difference in the length of day between summer
and winter. Days are longer in summer and shorter in winter.
o Effects of continents: This is more important in the northern hemisphere,
where there are very large areas of land.
oTemperate region has coniferous forest, grasslands and shrub lands.
oThe region as a whole is generally more developed than the other regions.
oMost of the worlds industries are found in this region.
 o Agriculture is also highly developed. This is true with fishing and forestry, too.
o The temperate region is, therefore, the most important producer of both
agricultural and industrial productions in the world.
o Temperate regions are classified the warm temperate and the cool temperate regions.
The warm temperate region includes:
The Mediterranean region areas.
The temperate monsoon lands.
The warm temperate grasslands of the southern hemisphere.
The temperate deserts (in the interiors of the continents).
The cool temperate region includes:
The temperate grasslands of the northern hemisphere.
The cool temperate western margins.
The cool temperate eastern margins.
The coniferous forest belts.
 A. Mediterranean Region

o located on the western coasts of the continents, particularly in the middle

latitudes (30° to 45° north and 30° to 40° south of the equator).
The major Mediterranean-region areas are:
o The surrounding area of (the shore of) Mediterranean sea
o Southwestern part of South Africa
o Central Chile
o Central California.
o Southwest and Southern Australia (Adelaide to Melbourne).
o Northern New Zealand.

Climate;
The climate is characterized by warm to hot, dry summers and mild to cool,
wet winters. Summer has off shore dry winds. But winter has on shore wet
easterly winds.
Focus: During the summer season, the Mediterranean lands are under the influence
of sub-tropical (Horse Latitude) high pressure. This means the dry trade winds
blow out from them and do not bring rain, but temperature is high. In winter,
the winds that blow over these areas are the onshore westerlies. These winds
blowing from the ocean bring rain to the Mediterranean-region areas, but the
temperature is low.

Natural Vegetation;
o The Maquis vegetation consists of small short trees with dense growth of shrubs
and scrubby(small bushes). The olive tree is the most common. Almost all kinds
of citrus fruits grow in the Mediterranean region.
o Trees are small and not growing well.
Human Activities
o Agriculture is highly diversified and specialized in the Mediterranean region
areas. The most important crops grown in the Mediterranean lands are grapes,
figs, oranges, apples, vegetables, olives, wheat and, in the wetter areas, rice.
Because of the dry hot summer, agriculture in the Mediterranean region depends
on irrigation.
o Transhumance is also practiced in the area. This is the practice among
pastoral farmers of moving their herds and flocks between two regions of
different climates.
o Mining: Gold and petroleum in California and copper in Chile. Italy is a
major producer of mercury. Chrome and coal are mined in Turkey.
o Manufacturing Industries: The existing industries process agricultural
products. Wine making, extraction of olive oil and fruit drying are some of
the industrial activities.
 B. Coniferous Forest Region/Taiga
oThis region lies approximately between 55° North and 70° North latitudes.
oThe coniferous forests are found only in the northern hemisphere.
 The major coniferous forest areas are:
Northern America
 Northern Norway, Sweden and Finland
Parts of Asia, South of the arctic circle and north of the temperate grassland.
Climate;
o The climate changes a lot from season to season. Winter is long and very cold.
For over half of the year, the mean monthly temperature is below zero. In winter,
the northern hemisphere is tilted away from the sun. As a result these lands get only
short periods of daylight.
o Summer is also a season of maximum rainfall. The rainfall is mainly cyclonic.
Even though the total rainfall is low, it is adequate for plant growth, as the rate of
evaporation is low.
Coniferous forest
 Natural vegetation;
o The vegetation in the region consists of conifer trees. The coniferous forests
have low species diversity. Single species of trees grow together in large stands
where there is suitable soil.
o The trees have adapted to the harsh climate of the region. They get and save
moisture through their long roots, spongy wood and needle shaped-leaves.
Human Activities;
oThe climate of the coniferous forests is not favorable for growing crops because
the growing season of this region is too short. The soils are not usually fertile.
o Forestry is one of the most important economic activities in these areas.
o Lumbering (the felling of trees) is usually done during winter.
•Mining: The coniferous forest region is also rich in several mineral deposits. Iron ore,
gold, cobalt, zinc, uranium, oil, copper and lead are the main minerals of the region.
Sweden, Canada, and the Russian Federation have rich iron ore deposits.
• Siberia is well known for its coal, oil and gas deposits.
o Generally, the coniferous forest region has a well-developed industrial
base. This is supported by the availability of many mineral deposits, rich forest
resources and cheap and abundant water power from rivers.

III Frigid (Cold) Zone

o The frigid zone is located between 66½° to 90°, both N and S of the equator.
o Common vegetations of this zone are lichens, mosses, grasses, cushion
plants, and low shrubs which spring to life during the short summer season.

o On the ice bound areas, such as Antarctica, there is no vegetation because

the temperature is not above the freezing point and there is no sufficient
sunlight that serves as a source of energy for life.

oThe most widespread people in the region are the Inuit (Eskimos), Indians,
Lapps, Chukchi, Koyaki, and Yakuts. They are found in Alaska, Canada,
Greenland, Finland, Norway, Sweden and Siberia.
  The frigid zone has two sub-regions these are;

a. Tundra
b. Polar ice caps.
a) Tundra Region
oThe word tundra refers to an area where the growth of trees is prevented due to low
temperatures and short seasons that restrict growth.
The tundra is a transitional zone between the polar ice caps and the coniferous forest
belt. Tundra is found only in the northern hemisphere.
Climate;
Tundra has two distinct seasons. These are the summer and winter seasons. During
the summer season, there is long daily duration of sunshine, but the
temperature is very low. Only three or four months have average temperatures
above the freezing point. This is because the sun’s rays are very slant, and therefore
lack heat. Winter is cold and long. During the daytime, the sky is dark, and stars
can be seen shining. The rainfall level in the tundra is low.
 Natural Vegetation;
o There is little or no vegetation in tundra areas. In places where the snow is
not thick, low forms of plants such as lichens, mosses and sedges grow during
the summer season. On the southern margins of the tundra lands, and in lower
areas, there are short trees and flowering plants.
Human Activities;
oThe tundra is a sparsely populated region. There are a few scattered tribes such
as Eskimos (Inuit), Lapps, Finns, Aleuts and Tunguses. These are primitive
peoples who have adapted themselves to the cold and difficult environment of the
tundra.
Human Activities;
There are no people living permanently in Antarctica. Only scientists and hunters visit this
cold continent. At present, the only resource of Antarctica is whale oil. But it is believed to
contain rich deposits of coal. The Arctic Ocean is rich in animals that can be used as sources
of food and material for clothing. The Arctic region is also important for military strategies.
For example, the USA has an airbase at Thule in Greenland.
B. Polar Ice Cap Region
o A polar icecap is a high latitude region of the earth that is covered with ice.
o The two polar ice caps are located near the North and South poles. These
natural regions include Greenland and the Arctic islands and Arctic Ocean in
the northern hemisphere and the continent of Antarctica and the South Sea in
the southern hemisphere.
Climate;
o Ice caps are generally characterized by negative temperatures. The average
temperature for each month of the year is less than 0°C. The precipitation is very
low and falls in the form of snow.
Natural Vegetation;
o Plant growth is impossible as the regions are permanently covered by ice and
snow. The soil of the region is permanently frozen. Except few areas the surface
is covered with ice.