The envelope of air that surrounds the earth is known as atmosphere. Atmosphere is essential for life on earth. It protects us and all living organism from harmful radiations of the sun like ultraviolet rays.

Atmosphere is divided into different layers according to temperature, pressure variation and composition. The main layers of the atmosphere from the surface of earth upward are:

  • Troposphere (0-10 km)
  • Stratosphere (10-50 km)
  • Mesosphere (50-85 km)
  • Thermosphere (85-500 km)

The most active region of the atmosphere is the troposphere, the layer of the atmosphere, which contains about 18% of the total mass of air and practically all the atmosphere’s water vapour. It is the thinnest layer of atmosphere and all the dramatic events of weather (such as rain) occur here.

Aquatic animals use dissolved air in water for respiration. Plants and animals depend on each other for exchange of oxygen and carbon dioxide from air.