-->The surface of the earth is a complex zone in which three main components of the environment meet, overlap and interact. The solid portion of the earth on which we live is called the Lithosphere. The gaseous layers that surround the earth, is the Atmosphere, where oxygen, nitrogen, carbondioxide and other gases are found. Water covers a very big area of the earth’s surface and this area is called the Hydrosphere. The Hydrosphere comprises water in all its forms, that is, ice, water and water vapour.

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

-->The solid portion of the earth is called the Lithosphere. It comprises the rocks of the earth’s crust and the thin layers of soil that contain nutrient elements which sustain organisms. 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.

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

-->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.

--> 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 is the largest continent. It covers about onethird of the total land area of the earth. The continent lies in the Eastern Hemisphere. 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 is much smaller than Asia. The continent lies to the west of Asia. The Arctic Circle passes through it. It is bound by water bodies on three sides.

--> Africa is the second largest continent after Asia. The Equator or 0° latitude runs almost through the middle of the continent. It is the only continent through which the Tropic of Cancer, the Equator and the Tropic of Capricorn pass.

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

--> The world’s longest river the Nile, flows through Africa.

--> North America is the third largest continent of the world. It is linked to South America by a very narrow strip of land called the Isthmus of Panama. The continent lies completely in the Northern and Western Hemisphere. Three oceans surround this continent.

--> South America lies mostly in the Southern Hemisphere.

--> The Andes, world’s longest mountain range, runs through its length from north to south. South America has the world’s largest river, the Amazon.

--> Australia is the smallest continent that lies entirely in the Southern Hemisphere. It is surrounded on all sides by the oceans and seas. It is called an island continent.

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

--> The earth is called the blue planet. More than 71 per cent of the earth is covered with water and 29 per cent is with land. 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. More than 97% of the Earth’s water is found in the oceans and is too salty for human use.

--> Oceans are the major part of hydrosphere. They are all interconnected. The ocean waters are always moving. The three chief movements of ocean waters are the waves, the tides and the ocean currents. The five major oceans are the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the Southern Ocean and the Arctic Ocean, in order of their size .

--> The Pacific Ocean is the largest ocean. It is spread over one-third of the earth. Mariana Trench, the deepest part of the earth, lies in the Pacific Ocean. The Pacific Ocean is almost circular in shape.Asia, Australia, North and South Americas surround it.

--> 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.

--> The Indian Ocean is the only ocean named after a country, that is, India. 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 encircles the continent of Antarctica and extends northward to 60 degrees south latitude.

--> 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.

--> The earth is surrounded by a layer of gas called the atmosphere. The atmosphere extends up to a height of about 1,600 kilometres. The atmosphere is divided into five layers based on composition, temperature and other properties. These layers starting from earth’s surface are called the troposphere, the stratosphere, the mesosphere, the thermosphere and the exosphere.

--> The atmosphere is composed mainly of nitrogen and oxygen, which make up about 99 per cent of clean, dry air. Nitrogen 78 per cent, oxygen 21 per cent and other gases like carbondioxide, argon and others comprise 1 per cent by volume. The density of the atmosphere varies with height. It is maximum at the sea level and decreases rapidly as we go up. The temperature also decreases as we go upwards. Air moves from high pressure to low pressure. Moving air is known as wind.

--> The biosphere is the narrow zone of contact between the land, water and air. It is in this zone that life, that is unique to this planet, exists.

--> 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.

Tick the correct answers.

(a) The mountain range that separates Europe from Asia is
(i) the Andes
(ii) the Himalayas
(iii) the Urals

(b) The continent of North America is linked to South America by
(i) an Isthmus
(ii) a Strait
(iii) a Urals

(c) The major constituent of atmosphere by per cent is
(i) Nitrogen
(ii) Oxygen
(iii) Carbon dioxide

(d) The domain of the earth consisting of solid rocks is
(i) the Atmosphere
(ii) the Hydrosphere
(iii) the Lithosphere

(e) Which is the largest continent
(i) Africa
(ii) Asia
(iii) Australia

Fill in the blanks.

(a) The deepest point on the earth is _____________ in the Pacific Ocean.
(b) The _____________ Ocean is named after a country.
(c) The _____________ is a narrow contact zone of land, water and air that supports life.
(d) The continents of Europe and Asia together are known as _____________.
(e) The highest mountain peak on the earth is _____________.