There is a cover of air all around the earth. This cover of air is known as atmosphere. This atmospheric cover extends to a height about 1600 kilometers from the earth surface. This atmosphere not fly away from the earth because it is held by the earth’s for gravity. The density of the air is maximum near the surface of: earth.

Composition of the atmosphere:

The atmosphere is made up of several gases. The composition of the air is as follows:

Nitrogen – 78%

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Oxygen – 21%

Argon, carbon dioxide and ozone-1%

Layers of the atmos­phere:

The atmosphere is divided into five layers which are as follows:

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Troposphere:

This is the lowest and the densest layer of the atmosphere. It extends to a height from 8 kilometers to 18 kilometers.

Stratosphere:

Stratos­phere lies just above the troposphere and extends up to the height of 50 kilometers. A part of the stratosphere is known as ozonosphere.

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Mesosphere:

This layer lies above the stratosphere and extends from 50 kilometers to 80 kilometers.

Ionosphere:

Beyond the mesosphere lies the layer of ionosphere. This layer lies between the heights of 80 kilometers to 300 kilometers. This layer is also known as the thermosphere.

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Exosphere:

The outermost layer of the atmosphere is called exosphere. The temperature in this layer is very high.