Blanket of air around the earth is called atmosphere. atmosphere has 5 layers namely troposphere , stratosphere , mesosphere , thermosphere and the exosphere. the stratosphere contains ozone layer which protects us from the ultraviolet rays of the sun.
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atmosphere is a layer of air surrounding around the earth.our atmosphere is necessary for the survival of organisms as it contains many important gases like oxygen. it is divided into five layers. starting from the earth's surface, they are:-

1. troposphere- this is the heaviest and lowermost layer of the atmosphere. it's average height is 13 km.
it is the most important layer of atmosphere as the air we breathe exist here. and almost all weather phenomenon takes place here. it prevents earth from becoming too hot and too cold.

2. stratosphere- it extends upto a height of 50 km. it is free from clouds and other weather phenomenon making it ideal for flying aeroplane. it's most important characteristics is that it contains ozone layer which protect us from harmful UV rays.
3.mesosphere- it extends upto 80 km. it's temperature can fall as low as -85 degree celsius. it's importance is that all meteors which enter into atmosphere from space burns here.

4. thermosphere- it extends upto a height of 450 km. ionosphere is a part of this layer. this layer helps in radio transmission.

5. exosphere- from this layer space starts. many light gases floats in it's surface.

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