CLASS- VI GEO. CHAPTER-5

CLASS- VI  GEO. CHAPTER-5

MAJOR DOMAINS OF THE EARTH

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     The earth is the only planet which has life. Human beings can live here because the  life sustaining elements of land, water and air are present on the earth.

·         Earth has three main components they are:-lithosphere,Atmosphere,Hydrosphere

·         Lithosphere:- i.The solid portion of the earth on which we live is called the Lithosphere.

ii. It comprises the rocks of the earth’s crust and the thin layers of soil that contain nutrient elements which sustain organisms.

·         Atmosphere:- The gaseous layers that surround the earth, is the Atmosphere, where oxygen, nitrogen, carbondioxide and other gases are found.

                   

·         Hydrosphere:-

     i.Water covers a very big area of the earth’s surface and this area is called the Hydrosphere.

    ii. More than 71 per cent of the earth is covered with water and 29 per cent is with land.So earth is called ‘blue planet’.

   iii. Hydrosphere consists of water in all its forms. As running water in oceans and rivers and in lakes, ice in glaciers, underground water and the water vapour in atmosphere,                                               .        all comprise the hydrosphere.

 iv. More than 97% of the Earth’s water is found in the oceans and is too salty for human use. A large proportion of the rest of the water is in the form of icesheets and glaciers                                        .       or under the ground and a very small percentage is available as fresh water for human use. Hence, despite being a ‘blue planet’ we face a shortage of water!!

   Biosphere :-The Biosphere is the narrow zone where we find land, water and air together, which contains all forms of life.

·           There are two main divisions of the earth’s surface. The large landmasses are known as the continents and the huge water bodies are called the ocean basins.

·         i.The level of seawater remains the same everywhere. Elevation of land is measured from the level of the sea,which is taken as zero.

·         ii. The highest mountain peak Mt. Everest is 8,848 metres above the sea level. The greatest depth of 11,022 metres is recorded at Mariana Trench in the Pacific Ocean.

Continents

·         There are seven major continents. These are separated by large water bodies. These continents are – Asia, Europe, Africa, North America, South America, Australia and Antarctica.

·         Asia

i.Asia is the largest continent. It covers about onethird of the total land area of the earth.

ii.The continent lies in the Eastern Hemisphere.

iii.The Tropic of Cancer passes through this continent. Asia is separated from Europe by the Ural mountains on the west.The combined landmass of  Europe and Asia is called the Eurasia (Europe + Asia).

·         Europe

i.Europe is much smaller than Asia. The continent lies to the west of Asia.

ii. The Arctic Circle passes through

it. It is bound by water bodies on three sides.

·         Africa

i.Africa is the second largest continent after Asia. The Equator or 0⁰ latitude runs almost through the middle of the continent. A large part of Africa lies in the Northern Hemisphere.

ii. it is the only continent through which the Tropic of Cancer, the Equator and the Tropic of Capricorn pass.

iii. The Sahara Desert, the world’s largest hot desert, is located in Africa. The continent is bound on all sides by oceans and seas.

iv. the world’s longest river the Nile, flows through Africa.

·         North America

i.North America is the third largest continent of the world.

ii.It is linked to South America by a very narrow strip of land called the Isthmus of Panama.

iii.The continent lies completely in the Northern and Western Hemisphere. Three oceans surround this continent.

·         South America

i.South America lies mostly in the Southern Hemisphere.

ii. The Andes, world’s longest mountain range, runs through its length from north to south.

iii.South America has the world’s largest river, the Amazon.

·         Australia

i.Australia is the smallest continent that lies entirely in the Southern Hemisphere.

ii.It is surrounded on all sides by the oceans and seas. It is called an island continent.

·         Antarctica

i. Antarctica, completely in the Southern Hemisphere, is a huge continent.

ii.The South Pole lies almost at the centre of this continent. As it is located in the South

Polar Region, it is permanently covered with thick ice sheets.

iii.There are no permanent human settlements. Many countries have research stations in Antarctica. India also has research stations there. These are named as Maitri and Dakshin Gangotri.

Oceans

i.Oceans are the major part of hydrosphere. They are all interconnected.

ii.The ocean waters are always moving. The three chief movements of ocean waters are the waves, the tides and the ocean currents.

iii. The five major oceans are the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the Southern Ocean and the Arctic Ocean.

Pacific Ocean

i.The Pacific Ocean is the largest ocean. It is spread over one-third of the earth.

ii.Mariana Trench, the deepest part of the earth, lies in the Pacific Ocean.

 iii.The Pacific Ocean is almost circular in shape. Asia, Australia, North and South Americas surround it.

The Atlantic Ocean

i.The Atlantic Ocean is the second largest Ocean in the world. It is ‘S’ shaped. It is flanked by the North and South Americas on the western side, and Europe and Africa on the eastern side. ii.The coastline of Atlantic Ocean is highly indented. This irregular and indented coastline provides ideal location for natural harbours and ports. From the point of view of commerce, it is the busiest Ocean.

The Indian Ocean

i.The Indian Ocean is the only ocean named after a country, that is, India.

 ii.The shape of ocean is almost triangular. In the north, it is bound by Asia, in the west by Africa and in the east by Australia.

The Southern Ocean

i.The Southern Ocean encircles the continent of Antarctica and extends northward to 60 degrees south latitude.

The Arctic Ocean

The Arctic Ocean is located within the Arctic Circle and surrounds the North Pole. It is connected with the Pacific Ocean by a narrow stretch of shallow water known as Berring strait. It is bound by northern coasts of North America and Eurasia.

 ATMOSPHERE

i.The earth is surrounded by a layer of gas called the atmosphere. This thin blanket of air is an integral and important aspect of the planet. It provides us with the air we breathe and protects us from the harmful effects of sun’s rays.

ii. The atmosphere extends up to a height of about 1,600 kilometres which is further divided into five layers based on composition, temperature and other properties such as:- troposphere, the stratosphere, the mesosphere, the thermosphere and the exosphere.

iii. The atmosphere is composed mainly of Nitrogen 78 per cent, oxygen 21 per cent and

other gases like carbondioxide, argon and others comprise 1 per cent by volume.

iv. Oxygen is the breath of life while nitrogen helps in the growth of living organisms. Carbon dioxide, though present in minute amount, is important as it absorbs heat radiated by the earth, thereby keeping the planet warm.

·         The density of the atmosphere varies with height. It is maximum at the sea level and decreases rapidly as we go up. You know, the climbers experience problems in breathing due to this decrease in the density of air. They have to carry with them oxygen cylinders to be able to breathe at high altitudes.

·         Air moves from high pressure to low pressure. Moving air is known as wind.

BIOSPHERE – THE DOMAIN OF LIFE

i.The biosphere is the narrow zone of contact between the land, water and air. It is in this zone that life.

ii. All the living organisms including humans are linked to each other and to the biosphere for survival.

·         Discharge of waste material into lakes and rivers makes the water unsuitable for human use. It also damages other forms of life.

·         Emission from industries, thermal power plants and vehicles, pollute the air. Carbon dioxide (CO2) is an important constituent of air. But increase in the amount of CO2 leads to increase in global temperatures.This is termed as global warming.

·         ISTHMUS

A narrow strip of land joining two landmasses.

STRAIT

A strait is a narrow passage of water connecting two large waterbodies like seas and ocean.