WHAT IS ATMOSPHERE?

• The air envelope that surrounds the earth is called the atmosphere. There are four major elements such as land, water, air and living organisms of environment. Among these four elements, the atmosphere is the most dynamic because it frequently changes period of few hours. The atmosphere is held on the earth by the force of gravity.
• The atmosphere is important to made life on earth, which is described below.

1. It provides protection against harmful rays of sun.
2. It saves earth from cosmic rays.
3. The atmosphere acts like a blanket or glass house of earth. It receives the radiation of sun but does not allow all the radiations to go outside from the atmosphere to keep earth warm for survival of organisms.
4. The atmosphere reduces the extremes of temperature between the day and the nights.

Composition of atmosphere :

• The atmosphere is a mixture of many type of gases. It consists about 78% Nitrogen, 21% Oxygen, 3% argon and 0.98% carbon dioxide, Hydrogen and other gases. The lower layer of the atmosphere contains water vapour. This layer added from the oceans, rivers, lakes and other water bodies present at earth.
• The atmosphere contains different layers which are given below.

1. Troposhere

2. Stratosphere

3. Mesosphere

4. Thermosphere

5. Exosphere

1. Troposhere :

The lowest layer of the structure of atmosphere is called troposhere. The upper limit of the troposhere is called tropopause. We are the part of this layer where we can live and survive. It contains most of our weather like clouds, rain, snow etc. The troposhere layer is more dense and extended up to 18 kms from surface of the earth. In this layer, the temperature of air decreases with height at an average rate of 1 degree C for 165 meters.

2. Stratosphere :

The layer above the tropopause limit is known as stratosphere. The thickness of stratosphere is about 40 to 50 kms. In this layer the temperature remains constant and then decreases with the height. This layer is free from clouds. The condition in this layer are ideal for flying of jets aircrafts and airplanes because it is very stable atmosphere layer. An ozone is also present in this layer which is absorb the harmful ultraviolet rays comes from the sun.

3. Mesosphere :

The layer above the stratosphere is known as mesosphere. It is a 30 KM thick layer. Here the temperature again decreases with height. It is the coldest place on earth and has an average temperature around -85 C. Just below the mesopause. 

4. Thermosphere :

This is the fourth layer and the second highest layer of earth's atmosphere. It extends from the mesopause and thickness of this layer is about 600 kms. Its lower part is called ionosphere. It contains irons. These particle reflects radio wave to the earth's surface and enable wireless communication.

5. Exosphere :

This is the fifth layer and the uppermost layer which is mostly covered by hydrogen and carbon dioxide. It extends from the thermosphere and thickness of these layer is about 600 kms.