Class 7 Geography

Air: Atmosphere

The thick envelope of air surrounding the earth is called the atmosphere. It is one of the natural components of the environment. The survival of all the living beings on this planet depends on the atmosphere.

Functions of Atmosphere:

Composition of Air

The air that we breathe is a mixture of many gases like oxygen, nitrogen, carbon dioxide, argon etc. The majority of the atmosphere is made up of nitrogen (78%) and oxygen (21%). Other gases that are present in small quantities are: Carbon dioxide (0.03%), Argon (0.93%) and Others (helium, hydrogen, ozone). Tiny dust particles are also present in the air, apart from these gases.

composition of air


It is the gas that is the most abundant in the air. Plants need nitrogen to make protein. Plants cannot take the gaseous nitrogen from air. Some bacteria live in soil and in roots of some plants. These bacteria take nitrogen from air and change it to a form so that plants can utilize nitrogen.


It is the second most plentiful gas in the air. Oxygen plays an important role for human beings, animals and plants in the following ways. Most of the living beings need oxygen for respiration. Green plants produce oxygen during photosynthesis.

The consumption of oxygen by human beings and animals is replenished by the production of the same by plants. Hence, the oxygen content in the air remains balanced. Indiscriminate felling of trees disturbs this balance.

Carbon Dioxide

It is another important gas. Green plants need carbon dioxide to carry out photosynthesis. Most of the living beings release carbon dioxide during respiration.

Photosynthesis is a process used by plants and other organisms to convert light energy, normally from the Sun, to chemical energy that can be later released to fuel the organisms' activities.

Structure of the atmosphere

Our atmosphere is divided into five layers which are: troposphere, stratosphere, mesosphere, thermosphere and exosphere.


It is the most important layer of the atmosphere. The air we breathe exists here. It has following features:


This layer is just above the troposphere and has the following features:


It is the third layer of the atmosphere and it lies above the stratosphere. It extends upto a height of 80 km. The burning of meteorites on entering from space occurs in this layer.


It is the fourth layer and the layer above the mesosphere. In this layer, temperature rises very rapidly with increase in height. Ionosphere is a part of this layer. Thermosphere has the following features:


It is the uppermost layer of the atmosphere. It has very thin air. Light gases like helium and hydrogen float into the space from here.