Major Domains of Earth

Learning Goals:


More than 71% of the earth’s surface is covered with water. But 97% of the total water on earth is available as saline water in oceans and seas. Saline water is not fit for human consumption. Out of the remaining 3% water; most of the water is in the form of ice in glaciers and icebergs. This leaves less than 1% of total water on earth available for human consumption. Hence, in spite of living on the Blue Planet we often face scarcity of water.


All oceans are interconnected and water in the oceans is always on move. Waves, tides and ocean currents are the three main movements of ocean water. There are five major oceans, viz. Pacific, Atlantic, Indian, Arctic and Southern oceans.

Pacific Ocean

This is the largest ocean. It is almost circular in shape. The Pacific Ocean is surrounded by Asia, Australia, North America and South America. Mariana Trench; the deepest place on the earth is in this ocean.

Atlantic Ocean

This is the second largest ocean. It is S-shaped. North America and South America are to the west of this ocean. Europe and Africa are on the east of this ocean. The coastline of this ocean is highly indented. The irregular and indented coastline provides ideal place for natural harbours and ports. Hence, this is the busiest ocean from commercial perspective.

Indian Ocean

Indian Ocean is the only ocean to be named after a country. This ocean is almost triangular in shape. Asia is towards north, Africa is towards west and Australia is towards east of this ocean.

Southern Ocean

This ocean encircles Antarctica. It extends northwards up to 60oS latitude.

Arctic Ocean

This ocean is within the Arctic Circle. It surrounds the North Pole. It is bound by the northern coasts of North America and Eurasia. The Arctic Ocean is connected to the Pacific Ocean by a narrow stretch of water called Berring Strait.


Atmosphere plays an important role in the environment on earth. Atmosphere is made of air which is composed of many gases, water vapor and dust particles.

Composition of Air: Air is mainly composed of nitrogen and oxygen. 78% of the air is composed of nitrogen, 21% is composed of oxygen and rest 1% is composed of carbon dioxide, argon and many other gases.

Role of Nitrogen: Nitrogen is important for plants because plants make many important molecules from nitrogen. Since we get food from plants, hence nitrogen is also important for us and for all other animals.

Role of Oxygen: Oxygen is required by living beings for respiration. Moreover, oxygen is also required for burning various fuels.

Role of Carbon Dioxide: Carbon dioxide is utilized by plants during photosynthesis. You may recall that photosynthesis is the process by which plants make food. Carbon dioxide also helps in trapping the heat from the sun and prevents the heat from escaping the atmosphere of earth. Thus, carbon dioxide helps in maintaining an ambient temperature on earth.

Layers of Atmosphere: The atmosphere can be divided into many layers. Troposphere is at the bottom. This is followed by stratosphere, mesosphere, thermosphere and exosphere.

The density of atmosphere changes with height. Air is at maximum density at the sea level and becomes rarer as we go higher. We are comfortable while breathing under normal pressure. When the atmospheric pressure becomes low, it becomes difficult to breathe. Atmospheric pressure is very low at high mountains. Due to this, mountaineers need to carry oxygen cylinders so that they can breathe comfortably at high altitude.

Difference in pressure also plays a role in wind movements. Air moves from high pressure to low pressure. Moving air is called wind.


The narrow zone of contact between the lithosphere, hydrosphere and atmosphere is called biosphere. Life exists in this zone. A variety of organisms exist on earth. All the living beings are linked to each other for their survival. They are also linked to various non-living things for their survival.

The organisms in the biosphere can be broadly classified into the Plant Kingdom and Animal Kingdom. The three domains of the earth interact with each other. They also affect each other in some ways or the other.

We need to take good care of our environment otherwise the existence of life would be in danger on our planet. For example; if we cut forests on large scale to clear land for human activities, this will lead to removal of topsoil. Removal of topsoil can be harmful in the long run because soil is necessary for agriculture and for plant growth. We create lot of waste which ends up polluting the environment.

Carbon dioxide is necessary for maintaining a certain temperature on earth. But if level of carbon dioxide increases beyond a limit, it results in increased temperature throughout the world. This is known as global warming. Burning of fuels; in automobiles and factories; results in increased levels of carbon dioxide in the atmosphere. Hence, we should be cautious while using various fuels.

We need to use our resources carefully in order to protect our environment.

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