Earth is a unique planet because the life is found only on this planet because of availability of water and air. The air is a mixture of several gases. The air encompasses the earth from all sides called the atmosphere.
It is connected with the earth due to the gravitational force of the earth. It helps in stopping the ultra violet rays harmful for the life and maintain the suitable temperature necessary for life. The air is essential for the survival of all forms of life on the earth. Besides many gases, water vapour and dust particles are also found in the atmosphere.
Composition of Atmosphere
The atmosphere is the mixture of different types of gases, including water vapour and dust particles. Nitrogen and Oxygen
are the two main gases containing 99% part of atmosphere.
Ozone Gas: The amount of ozone gas in the atmosphere is very little but it is very important. It protects the living beings by absorbing the ultraviolet rays of the sun.
Water Vapour: Gaseous form of water present in the atmosphere is called water vapour which is the source of all kinds of precipitation.
Dust Particles: Dust particles are generally found in the lower layers of the atmosphere and help in the condensation.
Structure of Atmosphere
The atmosphere extends upto about 1600 kilometres from the earths surface. The atmosphere can be divided into five layers according to the diversity of temperature and density:
- Troposphere
- Stratosphere
- Mesosphere
- Ionosphere
- Exosphere
Troposphere
This is the lowest layer of the atmosphere. The height of this layer is about 18 km on the equator and 8 km on the poles. This is the most important layer of the atmosphere because all kinds of weather changes take place only in this layer.
The environmental temperature decreases with increasing height of atmosphere. It decreases at the rate of 1°C at the height of 165 metre. This is called Normal lapse rate. The upper limit of the troposphere is called tropopause.
Stratosphere
This layer is above the troposphere. This layer is spread upto the height of 50 km from the Earth’s surface.
The temperature remains almost the same in the lower part of this layer upto the height of 20 km. After this the temperature increases slowly with the increase in the height. The temperature increases due to the presence of ozone gas in the upper part of this layer.
Weather related incidents do not take place in this layer. The air blows horizontally here. Therefore this layer is considered ideal for flying of aircrafts.
Mesosphere
It is the third layer of the atmosphere spreading over stratosphere. It spreads upto the height of 80 km from the surface of the earth. Its extent is 30 km. Temperature goes on decreasing and drops upto 100°C. Meteors or falling stars occur in this layer.
Ionosphere
This is the fourth layer of the atmosphere. It is located above the mesosphere. This layer spreads upto the height of 400 km from the surface of the earth. The width of this layer is about 300 km.
The temperature starts increasing again with increasing height in this layer. Electrically charged currents flows in the air in this sphere. Radio waves are reflected back on the earth from this sphere and due to this radio broadcasting has become possible.
Exosphere
This is the last layer of the atmosphere located above ionosphere and extends to beyond 400 km above the earth. Gases are very sparse in this sphere due to the lack of gravitational force. Therefore, the density of air is very less here.