Physical Environment Of The World. By Abdulaziz Hassan Farah

1. Chapter One
1 USTAD: ABDULAZIZ HASSAN AFARH

2. Unit Objectives
In this unit, you will learn about:
 The world
 The solar system
 The shape of the earth
 Latitudes and longitudes
 The forces of nature
 The atmosphere
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3. The World Map
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4. The World
We live on a planet which .is called the Earth.
The earth is like a ball moving in space. If you look up
from the earth you can see: the sun, the moon ,the
stars. All of these are objects in space. The sun,
moon, and earth are linked together in one system
called Solar system
 Continents
 Earth is made up of seven continents. A continent is
a large area of dry land on Earth surrounded by
ocean. The continents are Asia ,Africa, North
America, South America Antarctica, Europe, and
Australia.
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5. The Solar System
 Our solar system is the one we know the most about. The
Sun is at its centre. Our solar system includes everything
that orbits around the Sun. Planets, moons, asteroids,
comets, gas, and dust are all part of the solar system.
 There are eight recognized planets in the solar system.
 The Sun is a star—a ball of hot, glowing gas. It does not
have any solid parts. It is made up mostly of hydrogen
gas and helium gas. It affects weather and climate and it
is the source of life. The average distance from Earth to
the Sun is 93 million miles (150 million kilometres).
 Our planet (Earth) is the only planet that life exists.5

6. Our solar System
Nu
mb
ers
Planets
1 Mercury
2 Venus
3 Earth
4 Mars
5 Jupiter
6 Saturn
7 Uranus
8 Neptune
9 Pluto
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8. Some Facts The Planet Earth
The Shape of the Earth
Latitudes and Longitudes
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9. Latitudes and longitudes
Latitudes and longitudes are imaginary lines that are
marked on the globe .
The difference between latitudes and longitudes.
Latitudes
 lines that run around Earth from east to west.
 Latitudes are measured in degrees (º), and they are 180º
 Latitudes are parallel they never meet.
Longitudes
longitude are lines that circle Earth from north to
south.
Longitudes meet at the poles.
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10. A long time ago people thought that the earth was flat
but today it is proven fact that earth is round although
it is not perfect sphere.
The Size Of The Earth
 The surface area of the earth is 510 Km Square.
 The circumference of the earth at the equator is
40,066 Kms.
 The circumference at the poles is 39,992 Kms.
 71% of the earth is covered by water but the
percentage is expected to increase as the earth
continues to warm and the polar ice caps melt.
 The highest mountain in the world is Mount Everest
located in Himalayas, which is 8850m high.
 The longest mountain range in the world is the10

11.  The largest lake in the world is lake superior in North
America.
 The longest river in the world is Nile river.
 The largest ocean is the Pacific Ocean.
 The deepest ocean trench is the Mariana Trench of the
coast of the Philippines.
 The largest desert in the world is the Sahara desert.
 The earth is the home to more than six to seven billion
human beings and millions of species of animals and
plants.
 There are around 195 countries in the world .The last
country which was recognized as independent state was
South Sudan
 The largest country in the world is Russia and the
smallest is the Vatican City State.
 The Earth is the third planet from the sun. It makes one
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12. Earth’s Rotation And Time
The movement of the earth on its axis is called rotation.
The earth rotates once every 23 hours,56 minutes and
4.09seconds.This is rounded as 24 hours.
The map below shows how the lines of longitudes can be
used to divide the earth into time zones.
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13. International Time Zone
 As the earth rotates a new day comes and goes
the early day. For example , Wednesday reaches
our country , before it reaches New York.
 The international Date Line is the place where
the two days meet. To the west of this line it is a
day ahead of the area to the east of the line.
 The earth rotates in a circle .Thus one complete
rotation is 3600.
This takes 24 hours. Therefore, therefore it takes 4
minutes for the earth to turn through 1ºand 1hour turn
through 15º.
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14. With this information, it is possible to calculate the time
difference between two places . For example: it is
midnight in Hargeisa at 45º E
of the Prime Meridian What will be the time of Kigali at 30º
E of the Prime Meridian?
 The difference between 45º and 30º is 15º.
 The earth rotates through 15º in one hour.
 Therefore the time difference is one hour.
 Kigali is west Hargeisa Therefore the time will be earlier .
 The time of Kigali is one hour earlier than Hargeisa.
 Therefore when Hargeisa time is 11 Pm , the time of Kigali
is 10 pm.
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15. The Structure of the earth
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16. It is believed that the earth has four layers :
A. The Crust
B. The mantle
C. The outer core
D. The inner core
A. The crust
This is the thin outer layer of the earth. It is the part we
see. It is not smooth. Mountains rise from it and a
deep basin in it contains the oceans and seas of the
world.
B. The Mantle
This is the largest part of the earth’s interior. Stretching
from just under the crust.
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17. C. The Outer Core
This is very hot layer. The rock is not solid . It is sticky
like honey.
D. Inner core
This is the solid centre of the earth.
The Changing Forces Of The Earth
There are two forces which change the shape of the
earth and they are known as:
1.Internal forces which push out from inside the earth.
They cause faults, rift valleys, folding, earth quakes,
and volcanoes.
2. External forces erode the land surface. They can
wear away a hill and fill depressions. The major
external forces are running water, wind, moving ice,
sea waves and living organisms.
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18. The Forces Of Nature
A. Volcanoes
 the force pushing from inside earth sometimes causes cracks.
These cracks are called faults.
This gives a chance for liquid rock which is trapped inside the earth
to escape. It pushes out with great force and then cools and
builds hills called volcanoes.
When this molten rock comes out the volcano , we call it lava.
 The soil ,which forms on volcanoes is usually very fertile, so
many people live and farm on the sides of volcanoes.
B. Earthquakes
Sometimes the force inside the earth move the earth suddenly.
When earthquake occur in densely populated areas, there can
be great loss of life when buildings collapse
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19. The atmosphere
What is atmosphere?
Atmosphere is a thin gaseous layer of air that surrounds
the earth.
It extends outwards from about 1000 Km. The
atmosphere has five layers :
1. The troposphere
2. The stratosphere Which includes the ozone layer
3. Mesosphere
4. Thermosphere
5. Exosphere
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20. The Atmosphere Layers
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22. 1.The Troposphere
This is the nearest layer of the atmosphere to the earth. Most of
the clouds you see in the sky are floating in the troposphere.
It is where the weather changes take place. It is also the layer
which is get polluted first. Smoke and dust particles can block
sunlight from reaching the earth .
2. The Stratosphere
The stratosphere is the second major layer of the earth’s
atmosphere, just above the troposphere and below the
mesosphere. Jet airplanes fly in the stratosphere. Earth’s
ozone layer is in the stratosphere. The ozone layer absorbs,
or soaks up, harmful rays from the Sun.
Ozone is a gas layer which absorbs harmful ultraviolet rays
from the sun.If the ozone layer was not present ,life would
not be possible in our planet
In the last twenty years, scientists have noticed that ozone layer
is becoming thinner, and in some places , holes in the ozone
layer have occurred. This is being caused by the presence of
harmful gases which have been created and released into
atmosphere as a result of human activity.
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23. FactorysmokedarkenstheskyabovePrague,CzechRepublic.
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24. 3. Mesosphere
The mesosphere is the layer of the earth’s atmosphere
that is directly above the stratosphere and directly
below the thermosphere. In the mesosphere layer
,temperature decreases with increasing height.
4. The Thermosphere
The thermosphere is the biggest of all layers of the
earth’s atmosphere directly above the mesosphere and
directly below the exosphere. The temperature of this
layer rises up, and can reach up to 1,727º C.
5.The Exosphere
The exosphere is the uppermost layer of the earth’s
atmosphere. This layer does not contain any gas
particles.24