Physical Environment Of The Earth

Chapter One

Physical Environment Of The Earth

1USTAD: ABDULAZIZ HASSAN AFARH

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Unit Objectives

In this unit, you will learn about: The worldThe solar systemThe shape of the earthLatitudes and longitudesThe forces of natureThe atmosphere2

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The World Map

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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 systemContinentsEarth 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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The Solar SystemOursolarsystemisthe 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.TheSunisastaraball 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

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Our solar System

NumbersPlanets

1Mercury2Venus3Earth4Mars5Jupiter6Saturn7Uranus8Neptune9Pluto

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Some Facts The Planet EarthThe Shape of the EarthLatitudes and Longitudes

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Latitudes and longitudesLatitudes and longitudes are imaginary lines that are marked on the globe .The difference between latitudes and longitudes.Latitudeslines that run around Earth from east to west.Latitudes are measured in degrees (), and they are 180Latitudes are parallel they never meet.Longitudeslongitude are lines that circle Earth from north to south.Longitudes meet at the poles.

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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 EarthThe 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 the Andes range.

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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 full revolution around the sun every 365 days ,6 minutes and 9.45 seconds11

Earths Rotation And TimeThe 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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International Time ZoneAs 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 1and 1hour turn through 15.13

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With this information, it is possible to calculate the time difference between two places . For example: it is midnight in Hargeisa at 45 E of the Prime Meridian What will be the time of Kigali at 30 E of the Prime Meridian?

The difference between 45 and 30 is 15.The earth rotates through 15 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.14

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The Structure of the earth

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It is believed that the earth has four layers :The CrustThe mantleThe outer coreThe inner core A. The crustThis 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 MantleThis is the largest part of the earths interior. Stretching from just under the crust.

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C. The Outer CoreThis is very hot layer. The rock is not solid . It is sticky like honey.D. Inner coreThis is the solid centre of the earth.The Changing Forces Of The EarthThere 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.17

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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. EarthquakesSometimes 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 collapse18

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The atmosphereWhat 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 :The troposphereThe stratosphere Which includes the ozone layerMesosphereThermosphereExosphere19

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The Atmosphere Layers

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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 StratosphereThe stratosphere is the second major layer of the earths atmosphere, just above the troposphere and below the mesosphere. Jet airplanes fly in the stratosphere. Earths 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 planetIn 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.22

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Factory smoke darkens the sky above Prague, Czech Republic.

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3. MesosphereThe mesosphere is the layer of the earths atmosphere that is directly above the stratosphere and directly below the thermosphere. In the mesosphere layer ,temperature decreases with increasing height.4. The ThermosphereThe thermosphere is the biggest of all layers of the earths atmosphere directly above the mesosphere and directly below the exosphere. The temperature of this layer rises up, and can reach up to 1,727 C.5.The Exosphere The exosphere is the uppermost layer of the earths atmosphere. This layer does not contain any gas particles.

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