What is atmosphere?

            Atmosphere is the mass of air that envelops the Earth from all sides. It contains many gases and particles of various materials. Amongst the gases, nitrogen constitutes 78.1%, oxygen 21%, carbon dioxide and argon 0.03% and 0.9% respectively of the atmosphere. Along with these, the atmosphere also contains minute particles of water vapour, methane, nitrous oxide, carbon monoxide, hydrogen, ozone, helium, neon, and krypton and xenon gases. In addition, sand-particles, smoke, salt-particles, volcanic ash-particles, meteoric dust and pollen are also present in the atmosphere.

            The atmosphere is quite dense near the Earth’s surface, but becomes rarefied as one goes above it. It is estimated that the atmosphere extends up to a height of 1,000 km.

            It is made up of many layers. The pressure, density and temperature of the atmosphere vary with its distance from the Earth. At a height of 6 km, the air pressure is reduced to half of what it is at the Earth’s surface. Similarly, the temperature falls by 1°F for every 91 metres.

             On the basis of its physical properties, the atmosphere has been divided into the following five layers:

1. Troposphere: Troposphere extends from the Earth’s surface to a height of 17 km. It accounts for 75% of the total weight of the atmosphere. Almost all the living beings live in this part. As one goes up, the temperature decreases and becomes the minimum at a height of 10 km. Rains, clouds, storms and snow form in this very part. This is the most important atmospheric layer for living beings.

2. Stratosphere: Stratosphere extends up to a height of 48 km. Its upper portion contains ozone which absorbs ultra-violet rays coming from the sun. These rays are very dangerous for life. There are neither strong winds nor varying temperatures in this part.

3. Mesosphere: Mesosphere starts after a height of 50 km. Here the temperature is considerably low and it is the minimum at a height of 85 km.

4. Ionosphere: Atmospheric layer above the mesosphere and up to a height of about 500 km is called Ionosphere. It contains only charged particles. These charged particles reflect radio waves towards the Earth and make radio communication possible.

5. Exosphere: It is the outermost layer of the atmosphere. In this, the density of the atmosphere is very low. This part contains helium and hydrogen. So, the temperature is very high here.

             The atmosphere is extremely useful for life. Without it we cannot survive. It protects us from the dangerous radiations of the Sun. The meteors also get destroyed after getting burned due to the atmospheric friction.