What is the Atmosphere?
- An atmosphere is a layer of gases surrounding a planet or other material body of sufficient mass that is held in place by the gravity of the body.
- The envelope of air that completely surrounds the earth is known as the atmosphere. The atmosphere extends to about 1000 from the surface of the earth. But 99% of the total mass of the atmosphere is found within 32 km. This is because the atmosphere is held by the gravitational pull of the earth.
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- Nitrogen – 78%
- Oxygen – 20.93% ~ 21%
- Argon -0.93%
- Carbon-dioxide – 0.03%
- Neon – 0.0018%
- Helium – 0.0005%
- Ozone – 0.0006%
- Hydrogen – 0.00005%
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Layers of the Atmosphere
There are five distinct layers of the atmosphere –
- Thermosphere / Ionosphere
- This is the first layer of the atmosphere.
- It extends to a height of 18 km at the equator and 8 km at the poles.
- In this layer, temperature decreases with height. This is due to the fact that the density of air decreases with height and so the heat absorbed is less.
- It contains more than 90% of the gases in the atmosphere. Since most of the water vapor forms clouds in this layer, all-weather changes occur in the troposphere(“Tropo” means “change”).
- The height at which the temperature stops decreasing is called Tropopause. Here the temperature may be as low as -58 degrees Celsius.
- This is the second layer of the atmosphere.
- It extends from the tropopause to about 50 km.
- Temperature increases due to the absorption of the ultraviolet radiation of the Sun by Ozone present in this layer.
- The temperature slowly increases to 4 degrees Celsius.
- This layer is free from clouds and associated weather phenomena. Hence, it provides ideal flying conditions for large jet planes.
- Above the stratosphere lies the Mesosphere.
- The mesosphere extends to a height of 80 km.
- Here the temperature decreases again, falling as low as -90 degrees Celsius. The end of this layer is known as the Mesopause.
- This layer extends to a height of about 640 km.
- This increase in temperature is due to the fact that the gas molecules in this layer absorb the X-rays and Ultraviolet radiation of the Sun.
- The electrically charged gas molecules of the thermosphere reflect radio waves from the Earth back into space.
- Thus, this layer also helps in long-distance communication.
- The Thermosphere also protects us from meteors and obsolete satellites because its high Temperature burns up nearly all the debris coming towards the Earth.
- The Exosphere extends beyond the Thermosphere up to 960 km.
- It gradually merges with interplanetary space.
- The temperatures in this layer range from about 300 degrees Celsius to 1650 degrees Celsius.
- This layer contains only traces of gases like oxygen, nitrogen, argon, and helium because the lack of gravity allows the gas molecules to escape easily into space.
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