Geography: Atmosphere, Composition and Layers of the Atmosphere of the Earth

Geography: Atmosphere of Earth

Composition of the Atmosphere

1. Nitrogen - 78%
2. Oxygen - 21%
3. Argon -0.93%
4. Carbon dioxide - 0.03%
5. Neon - 0.0018%
6. Helium - 0.0005%
7. Ozone - 0.0006%
8. Hydrogen - 0.00005%

 

Layers of the Atmosphere

There are five distinct layers of the atmosphere -

1. Troposphere
2. Stratosphere
3. Mesosphere
4. Thermosphere
5. Exosphere

 

Layers of the Atmosphere in detail

(a) Troposphere

• 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 gases in the atmosphere.
• Since most of the water vapour form 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 degree Celsius.

 

(b) Stratosphere

• 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 radiations of the Sun by Ozone present in this layer. The temperature slowly increases to 4-degree Celsius.
• This layer is free from clouds and associated weather phenomena. Hence, it provides ideal flying conditions for large jet planes.

 

(c) Mesosphere

• 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-degree Celsius.
• The end of this layer is known as the mesopause.

 

(d) Thermosphere

• 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 the space. Thus, this layer also helps in long distance communication.
• The thermosphere also protects us from meteors and obsolete satellite because its high Temperature burns up nearly all the debris coming towards the Earth.

(e) Exosphere

• The exosphere extends beyond the thermosphere up to 960km.
• It gradually merges with interplanetary space.
• The temperatures in this layer range from about 300 degree Celsius to 1650 degree 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