Structure and Composition of Atmosphere

Sep 16 • Notes • 4998 Views • 1 Comment on Structure and Composition of Atmosphere

In the Solar System  the Earth is the only planet that has life. The earth is surrounded by the thin envelope of gasses which is known as Atmosphere. It protects the life on the planet. We take air from this atmosphere to breathe hence it protects us from heat and harmful ultra violet radiations. By composition, air contains 78.09% Nitrogen, 20.95% Oxygen, 0.93% Argon, 0.039% Carbon dioxide, and other gases.

Layers of Atmosphere:-

Layers of Atmosphere

Different layers of Atmosphere

There are five layers in the atmosphere

  • Troposphere
  • Stratosphere
  • Mesosphere
  • Thermosphere
  • Exosphere

I. Troposphere :


1st layer of Atmosphere

It is the bottom most layer which is closest to the earth. The bottom part of troposphere is warm as it is closest to the earth and the temperature decreases with height. It extends from 8-20 km above the earth’s surface. As we go up, the temperature varies from 15 degree Celsius to 65 degree Celsius  In this region, almost all the weather occurs hence also known as weather and climate layer. This is the layer where we live. The top of the troposphere or the boundary which separates troposphere and stratosphere is  called as Tropopause.

II. Stratosphere :


2nd layer of Atmosphere

Above the troposphere the next layer is the stratosphere. It extends from the Tropopause to about 50 km. This is also known as Ozone region as it contains maximum amount of the ozone in the atmosphere. There is an increase in the temperature with height as the ozone layer absorbs harmful ultra violet radiations but the temperature still remains below freezing.

The ozone layer protects us from skin cancer by absorbing UV rays. However chemicals  such as CFCs or Freon’s that are used in refrigerators, reduces the amount of ozone in the atmosphere. This is the layer where jet aircrafts and balloons fly. The top of the stratosphere or the boundary which separates stratosphere and mesosphere  is called as Stratopause.

III. Mesosphere :


3rd layer of Atmosphere

This layer extends from 50 -80 km from the Stratopause. The effect of ultra violet also becomes less, hence , as the height increases, the temperature decreases. The temperature decreases, on an average, from -17 degree Celsius to -122 degree Celsius, hence this is the coldest part in the earth’s atmosphere. It is the layer where meteors burn up upon entering the atmosphere. Both the stratosphere and the mesosphere are considered the middle atmosphere.

IV. Thermosphere :


4th layer of Atmosphere

Above the mesosphere the next layer is the Thermosphere. This layer is also called as upper atmosphere. It extends upto 600km above the earth. We have seen that the temperature inversion in the stratosphere is caused by the absorption of ultra violet rays, but here , the case is different. Here the temperature inversion is caused by the low density of molecules. Temperatures rises sharply in the lower thermosphere (below 200 to 300 km altitude), then hold steady with increasing altitude above that height. The molecules are far apart in the layer and temperature rises upto 2000 degree Celsius.

V. Exosphere :


5th layer of Atmosphere

It is the outer most layer of the atmosphere. It is composed mainly of hydrogen, helium and other heavy gases. It extends from the top of the thermosphere at about 10,000 km. In this layer, the particles are far apart from each other.

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Introduction and Principal of UV

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