The atmosphere is divided into five layers.
The first atmospheric layer, lying closest to the earth's surface, is the Troposphere. The characteristic feature of the Troposphere is its great density present in its composition. Another characteristic of this layer is that temperature decreases at a nearly uniform rate with increased altitude.
The upper boundary of troposphere varies depending upon geographic latitude. The greatest height (thickness) of the troposphere is recorded in the equatorial and tropical zones where it reaches 16 to 18 km, while in the polar and circumpolar regions it is located at an average altitude of 8 to 10 km. Its average height is 13 km.
The air we breathe exists here. Almost all the weather phenomena like rainfall, fog and hailstorm occur in this layer.
The stratosphere lies between about 8-18 km to about 50-55 km. This layer is almost free from clouds and associated weather phenomenon, making conditions most ideal for flying aeroplanes.
In the stratosphere, temperature has a tendency to rise. This is due to the presence of Ozone. Ozone layer absorbs ultraviolet radiation from the sun and converts it into heat and chemical energy.
Above stratosphere, the Mesosphere is the third layer of the atmosphere whose height is about 80 km. The regular temperature rise that occurs in the stratosphere stops at its upper boundary (at an altitude of 50-55 km). Within the mesosphere the temperature fall is noted again. Meteorites burn up in this layer on entering from the space.
In thermosphere, temperature rises very rapidly with increasing height. Ionosphere is a part of this layer. It extends between 80-400 km. This layer helps in radio transmission.
The upper most layer of the atmosphere is known as exosphere. This layer has very thin air. Light gases like helium and hydrogen float into the space from here.