Atmosphere is a multilayer blanket of various gases such as N2 (78.80%), O2 (20.95%), Ar(0.93%), CO2 (0.03%), water vapor and some other gases. This envelope extends from earth's crust up to a distance of 1000 km.
It behaves like an insulator preventing the escape of heat from earth surface, filters harmful UV. Rays, and helps in stabilization of weather and climate. On the basis of composition and temperature atmosphere is divided into five layers.
(a) Troposphere
(b) Stratosphere
(c) Mesosphere
(d) Thermosphere
(e) Exosphere
(A). Troposphere:
It is lower most layer of the atmosphere and extends up to height of 12-18 km. it contains about 75% of total atmospheric mass. Formation of clouds, storms and thermal convection (weather and climate changes) occur in this layer. The approximate decrease of temperature is 6 C with 1 Km increase in the height.
(B). Stratosphere:
It extends up to 50 km. This layer is rich is ozone gas which is present in ozone sphere. Here, ozone is formed by decomposition oxygen to atomic oxygen by solar radiation and combination with oxygen to from ozone.
O2 + Solar rays = 2O
O2 + O = O3
Ozone layer acts as a protective umbrella to absorb the UV rays of the sun.
(C). Mesosphere:
It starts above the stratosphere and extends to an altitude of 85 km. This layer is characterized by fall of temperature due to absence of radiation absorbing species (ozone). Temperature may reach as low 93 C with increase of altitude. Main chemical species present here as N2, O3, O2+ and NO+.
(D). Thermosphere (Ionosphere):
It extends up to a height of 500 km from surface of earth and is characterized by increase in temperature with height. In this sphere U.V. radiation and cosmic rays causes ionization of molecules and thus Components like O2+, O+ and NO+ is formed. These ions reflect back radio waves back to earth surface and enable us to have wireless communication.
(E). Exosphere:
It is upper most layers and extends up to height of 1600m from earth surface. It has very high temperature and contains H2 and He.