Atmosphere is a mixture of gases, Water vapour and dust particles in different Proportions. Nitrogen (78%) and Oxygen (21%) are permanent gases of the atmosphere. They constitute 99% of the total composition And their percentages always remain the Same without any change. The remaining one Percentage is occupied by Argon (0.93%), Carbon-di-oxide, (0.03%), Neon (0.0018%), Helium (0.0005%), Ozone (0.00006%) and Hydrogen (0.00005%). Krypton, Xenon and Methane are also present in trace. Water vapour (0 – 0.4%) is also found in the Atmosphere, which plays an important role in Predicting weather phenomenon. The other Solid particles present in the atmosphere Includes dust particles, salt particles, pollen Grains, smoke, soot, volcanic ashes etc.,.

Oxygen is most important for living Organisms. CO2 absorbs heat and keeps the Atmosphere warm by insulation and radiation. Nitrogen acts as a diluent and is chemically Inactive. Ozone helps in protecting the earth From harmful ultra violet radiation. The solid Particles in the atmosphere acts as nuclei On which water vapour condense to form Precipitation.

Structure of the Atmosphere:

The atmosphere is thick near the earth Surface and thins out until it eventually merges With space. The five atmospheric layers are: Troposphere, stratosphere, Mesosphere, Thermosphere and Exosphere.

Troposphere:

The lowest layer of the atmosphere is the Troposphere. The Greek word ‘tropos’ means‘turn’ or change. The layer extends up to 8 kmsAt the poles and up to 18 kms at the Equator. The Temperature decreases with increasing height. Almost all weather phenomenons take place in this layer. Hence it is called weather making Layer. The upper limit of the troposphere is called as tropopause.

Stratosphere:

Stratosphere lies above the troposphere. It extends to a height of about 50km above Earth surface. Since this layer is a concentration of ozone molecules, it is also referred as Ozonosphere. The temperature increases with increase in height in this layer. Large jet Planes normally fly here. The upper limit of the Stratosphere is called as stratopause.

Mesosphere:

Mesosphere extends between 50km and 80km. The temperature decreases with increasing height. Most of the meteors nearing the earth get burned here. The upper most limit of the mesosphere is the mesopause.

Thermosphere:

Thermosphere exists above the mesosphere. It extends to about 400 km. The composition of Gases in the lower thermosphere is more or less uniform, hence it is called “Homosphere”. The Upper portion of the thermosphere has uneven Composition of gases and hence it is referred as “Heterosphere”. Here the temperature increases with increasing height. Ionosphere is a layer ofThe thermosphere that contains Ions and free Electrons. Radio waves transmitted from earth are reflected back to earth from this layer.

Exosphere:

The uppermost layer of the atmosphere is Called exosphere. This layer is extremely rarefied with gases and gradually merges with the outer Space. This zone is characterized by aurora Australis and aurora borealis.