What is the atmosphere?
Atmosphere is the blanket of air that envelops the earth. It contains many gases and particles of various materials. Among the gases of the atmosphere, nitrogen constitutes 78%, oxygen 21%, carbon dioxide and other gases 1%. The atmosphere also contains minute particles of water vapor, 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 dense near the earth’s surface, but becomes rarefied as one goes higher up. It is estimated that the atmosphere extends up to the exosphere, which is more than 500 kilometers above the earth’s surface. It is made up of many layers. The pressure, density and temperature of the atmosphere vary with its height above the earth. At a height of 6 kilometers, the air pressure is reduced to half of what it is at the earth’s surface. Similarly, the temperature falls by 1 degree Fahrenheit for every 91 meters we ascend.
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 about 17 kilometers. It accounts for 75% of the total weight of the atmosphere. It is the most important layer, as almost all the living beings inhabit this part. As one goes higher, the temperature falls. Rain, clouds, storms and snow are formed in this part.
2. Stratosphere: Stratosphere extends up to a height of about 48 kilometers. Its upper portion contains ozone, which absorbs ultra-violet rays coming from the sun. These rays are very dangerous for living organisms. There are neither strong winds nor varying temperatures in this layer.
3. Mesosphere: Mesosphere starts after a height of 50 kilometers. Here the temperature is significantly low and it is the minimum at a height of 85 kilometers.
4. Ionosphere: The atmospheric layer above the mesosphere and up to a height of about 500 kilometers is called ionosphere. It contains only charged particles, which reflect the radio waves towards the earth and make radio communication possible.
5. Exosphere: It is the outermost layer of the atmosphere. Here the density of the atmosphere is very low. This part contains helium and hydrogen, and hence the temperature is very high in this layer.
The atmosphere is extremely useful for life on earth. Without it, no living being can survive. It protects us from the dangerous radiations of the sun. Almost all meteors radiations of the sun. Almost all meteors falling towards the earth get destroyed; they burn up due to resistance ad friction offered by the atmosphere.