GK : THE WORLD

The Atmosphere:
The air is composed mainly of nitrogen (78%) and oxygen (21%) with small proportions of carbon dioxide, water vapour and rarer gases like argon and neon. Atmosphere is 200 miles thick, but nine-tenths of the air composing it is found within 12 miles, and half within 3½ miles of the earth’s surface. We are concerned mainly with the lower layer of troposphere. The upper layers in the ascending order are Stratosphere, Mesosphere and Ionosphere. Troposphere extends to a distance of about ten kilometres. 

Stratosphere is a region extending from an altitude of about 11 Km to 50 Km above the earth. The upper part of stratosphere has plenty of ozone which protects us from the fatal effects of Sun’s ultraviolet radiation. Mesosphere is the next layer extending from 50 o 80 Kms above the earth. It is a very cold region.  Ionosphere extends from about 60 Kms upwards. It includes Thermosphere and Exosphere which marks the outer limits of the earth’s atmosphere.

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