Class 6 Geography

Major Domains of Earth: Atmosphere & Biosphere

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

Pie Charts showing 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.

Saving the Environment

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.