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ICSE Class 9 Geography Question 15 of 19

Composition and Structure of the Atmosphere — Question 5

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Question 2(a)

Describe the structure of the atmosphere based on the picture given below.

Describe the structure of the atmosphere based on the picture given below. Total Geography ICSE Class 9
Answer

The atmosphere consists of concentric layers of air. On the basis of the characteristics of temperature and air pressure, it can be divided into four thermal layers — Troposphere, Stratosphere, Mesosphere and Thermosphere. The Thermosphere is divided into Ionosphere and Exosphere. The four layers are briefly described below:

  1. Troposphere — It is the lowermost and densest layer. Its height varies from 18 km at the Equator to 8 km at the Poles.
  2. Stratosphere — This layer lies above the Troposphere. It extends to a height of 50 km from sea level. The Ozone layer lies within the stratosphere. Ozone is generally found between the altitudes of 20 and 50 km.
  3. Mesosphere — This layer lies above the Stratosphere. It extends to a height of 80 km from ground level.
  4. Thermosphere — It lies above Mesosphere and consists of two parts:
    1. Ionosphere — It extends up to a height of about 400 km.
    2. Exosphere — It is the uppermost layer of the atmosphere. It lies between 400 to 1500 km above the earth.