The atmosphere refers to gaseous layers around earth which support life on the earth and saves us from the environments of outer space. The atmosphere absorbs most of the harmful radiations (cosmic rays, ultraviolet rays) from, the outer space and absorbs infra red rays to sustain life on the earth.
The portion of the atmosphere closest to the earth is called troposphere which extends upwards to a distance of about 11 kilometers and contains 70% of the mass of atmosphere.
The important chemical constituents of the troposphere are N2, 02, C02 noble gases and water vapours. The stratosphere layer extends up to about 40 km and is very important because this layer consist of Ozone which absorbs ultraviolet radiation. Thus stratosphere absorbs the harmful ultraviolet radiation which protects us from the harmful radiations of sun.
The region beyond stratosphere, is dominated by positive ions such as and frees electrons and is known as ionosphere. The formation of ions takes place due to the ultraviolet radiation received from the sun and in the absence of ultra violet radiation at night, the + ve ions recombine with the electrons to from neutral species.
Mesosphere extends from about 40 km to an altitude of about 80 km. The low level of ozone in this layer causes decrease of temperature in this layer.
Thermosphere extends beyond 80 km and the atmosphere gases split into atoms and undergo ionization after absorption of solar radiations. In this layer the temperature increases with increase in altitude and shows a maximum of 1200°C.