Chapter 3

                           Air: It is the breath of life!


The earth has a blanket of air!

Earth is the only known planet with an atmosphere that can support life. The atmosphere is a blanket of gases surrounding the earth.

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Atmosphere: What does it contain? 

Two gases make up the bulk of the earth's atmosphere by volume: nitrogen(78 per cent) and oxygen(21 per cent). The remaining one per cent is composed of' 'trace' gases, the most prevalent of which is argon. The rest of the trace gases, although present in only minute amounts, are very important to life on earth.Two in particular, carbon dioxide and ozone, have a large impact on atmospheric processes.Another gas, water vapour, also exists in small amounts. It varies in concentration from being almost non-existent over desert regions to about 4 per cent over the oceans. Water vapour is important in the formation of weather. The atmosphere has four layers.


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Atmosphere: The layers

Based on temperature changes into four layers: The troposphere, stratosphere, mesosphere and thermosphere.


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Troposphere- The layer of the atmosphere closest to the earth's surface extending to an average distance of about 12 km from sea level.

Stratosphere- The layer above the troposphere up to about 50 km above the earth's surface.

Mesosphere- The air that occupies the space above the stratosphere up to about 80 km above the earth's surface.

Thermosphere- The air that occupies the space above the mesosphere up to about 600 km above the earth's surface.

Acid rain

Rain containing traces of mineral acids, such as sulphuric acid and nitric acid is called acid rain. These acids are formed when the air is highly polluted with gases like sulphur dioxide and nitrogen dioxide, due to excessive burning of coal and petroleum products. The above mentioned gases dissolve in rain droplets and cause acid rain. The acid rain can cause extensive damage to the forests and crops as they die. Furthermore, the acids in acid rain react chemically with the building materials of houses and historical monuments. Thus, the building gradually decay.


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