Domains of the Earth Geography notes for UPSC Examination

Geography notes UPSC, Geography optional Subject notes UPSC, Geography notes IAS, Geography optional Subject notes IAS, domain of earth, continents, oceans, lithosphere, hydrosphere, atmosphere, biosphere

Major domains of the earth

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. 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, carbon dioxide 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.

Geography notes UPSC, Geography optional Subject notes UPSC, Geography notes IAS, Geography optional Subject notes IAS, domain of earth, continents, oceans, lithosphere, hydrosphere, atmosphere, biosphere


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. All the oceans of the world are connected with one another. 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 one-third 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. A large part of Africa lies in the Northern Hemisphere. 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. It is larger than the combined area of Europe and Australia. 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. A large proportion of the rest of the water is in the form of ice-sheets and glaciers or under the ground and a very small percentage is available as fresh water 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 four major oceans are the Pacific Ocean, the Atlantic Ocean, the Indian 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 under the Pacific Ocean. The Pacific Ocean is 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 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 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 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 Bering Strait. It is bound by northern coasts of North America and Eurasia.

Geography notes UPSC, Geography optional Subject notes UPSC, Geography notes IAS, Geography optional Subject notes IAS, domain of earth, continents, oceans, lithosphere, hydrosphere, atmosphere, biosphere


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. The atmosphere extends up to a height of about 1,600 km.

The atmosphere is divided into five layers based on composition, temperature and other properties. These layers starting from earth’s surface are 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 carbon dioxide, argon and others comprise 1% 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 climbers experience problems in breathing due to this decrease in the density of air. The temperature also decreases as we go upwards.

The atmosphere exerts pressure on the earth. This varies from place to place. Some areas experience high pressure and some areas low pressure. 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 exists. All the living organisms including humans are linked to each other and to the biosphere for survival. The organisms in the biosphere may broadly be divided into the plant kingdom and the animal kingdom.

The three domains of the earth interact with each other and affect each other in some way or the other. For example, cutting of forests for fulfilling our needs of wood, or clearing land for agriculture may lead to fast removal of soil from slopes. Similarly earth’s surface may be changed due to natural calamities like earthquakes or tsunamis.

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. There is thus, a need to limit the use of resources of the earth to maintain the balance of nature between the domains of the lithosphere, the atmosphere and the hydrosphere.

Points to Remember

  1. Mercury, Venus, Earth and Mars are known as’ Inner Planets’ whereas Jupiter, Saturn, Uranus and Neptune are known as “Outer plants”.
  2. Planets bigger than the earth are Jupiter, Saturn, Uranus and Neptune.
  3. Earth and Venus have almost same size, hence these two are known as’ Twin planets”
  4. All planets rotate in the same direction in which they revolve except Venus and Uranus.
  5. Saturn is surrounded by three luminous, concentric rings.
  6. Earth has the maximum density of 5.52 in the solar system while the Saturn has the least density of 0.69.
  7. According to gravity Jupiter stands first followed by Neptune, Uranus, Saturn and Earth.
  8. Mercury and Venus have no satellite.
  9. Neptune’s atmosphere has poisonous gases like methane, ammonia, etc.
  10. Comets revolve around the Sun and when broken are converted into “Meteors”.
  11. Earth is spherical in shape with compression at the poles and a bulge at the equator. Hence earth is an oblate spheroid or called a Geoid.
  12. A solar day is greater than a sidereal day by 4 minutes.
  13. Each degree of latitude is equals to 111 km.
  14. A person crossing International Date Line from the East to West loses one day.
  15. Mercury is the nearest planet to Sun.
  16. Venus is the nearest planet to Earth.
  17. Venus is the hottest planet; its atmosphere contains 97% CO2.
  18. Jupiter is the biggest planet.
  19. Venus is the brightest planet.
  20. Earth is the blue planet.
  21. Mars is the Red planet.
  22. Venus is the Morning and Evening Star.
  23. Pluto is the double planet.
  24. Saturn and Uranus are known as the planets with rings.
  25. Mercury has the maximum diurnal range of temperature.
  26. Saturn has maximum no. of satellites.
  27. Pluto has the most eccentric orbit.
  28. Jupiter is the fastest rotating planet.
  29. Venus is the slowest rotating planet.
  30. Venus has the same period of rotation as revolution.
  31. The length of the day is nearly same on the planet Mars as that of the Earth.
  32. Jupiter, Saturn, Uranus and Neptune are the Jovian planets.
  33. The angle of inclination of Mars is nearly same as that of Earth.
  34. Jupiter, Saturn, Uranus and Neptune are the outer planet.
  35. Mercury, Venus, Earth and Mars are the inner planets.

36.Venus rotates from East to West.

37.Uranus rotates from North to South.

  1. Mercury is the fastest revolving planet.
  2. Pluto is the slowest revolving planet.
  3. Planet revolves around the sun in Anticlockwise direction.
  4. “Hydra” is the largest constellation.
  5. The nearest galaxy. “Andromeda” is 22, 00,000 Light years away.
  6. Existence of galaxies beyond Milky Way was first demonstrated by Edwin Hubble.

44. Galaxies are also called “Islands of universe”

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