ICSE Class 9 Answered

The atmosphere is divided into five layers beginning from the surface of the Earth. These are:

Troposphere

• It is the most important layer of the atmosphere and it extends up to 13km from the surface of the Earth.
• Oxygen, that we breathe exists in this layer of the Earth.
• The temperature decreases in this layer with the increase in height.
• All weather phenomena like rainfall, hail and fog occur in this layer as the clouds are formed in this layer.
• The upper limit of the troposphere is known as the tropopause. Temperature may be as low as -58⁰C
  at this level.

Stratosphere

• This layer of atmosphere lies above the troposphere and it extends up to a height of 50km.
• Airplanes fly in this layer, as this layer is free from clouds and other weather phenomena. This layer is also free from water vapour and dust particles.
• Stratosphere contains a layer of ozone gas which protects us from the harmful ultra violet rays of the Sun.
• In the higher levels of the stratosphere, the temperature increases with height due to the absorption of UV rays by the ozone in the layer.
• The upper part of the stratosphere is known as stratopause.

 Mesosphere

• This is the third layer of the atmosphere and it lies above the stratosphere up to a height of 80kms.
• It is in this layer that meteorites burn when they enter into the atmosphere from space.
• The upper layer of the mesosphere is known as the mesopause.

Thermosphere or Ionosphere

• This layer extends from 80-400km.
• Temperature increases drastically in this layer and can go up to 1,4800C.This is because the molecules in this layer absorb the Sun’s UV rays.
• Thermosphere helps in the transmission of radio waves as the latter is reflected back to the Earth by this layer.

 Exosphere

•  It is the uppermost layer of the Earth.
• It has very thin layer of air.
• Light gases like helium and hydrogen float into space from this layer due to the lack of gravity.
• This layer extends from 480 km to 960 km above the Earth.
• Temperature increases with height in this layer. The temperature may well go beyond 5500⁰C