The atmosphere is composed of the following belts (layer):
1. Troposphere : This atmospheric layer lies closed to the earth’s surface. It extends to a height from 8 km (Near the Poles) to 18 km (Near the Equator). Most of the weather phenomena occur in this layer of atmosphere. It is a dusty zone containing much water vapour and clouds.
2. Stratosphere : The next layer lying above the troposphere is the stratosphere. The thickness of this layer varies about 62 km (at the Equator) and about 72 km (at the Poles.) Temperature is almost constant. There is no clouds, water vapour of dust in this layer due to constant temperature in the vertical direction. Ozone gas is found in abundance which absorbed harmful ultra-violet radiation from the sun.
3. Mesosphere : This third layer is above the stratosphere. ‘Meso’ meaning the intermediate, this region is marked by decrease in temperature with height. Temperature decrease from about 0°C at Stratopause to 100°C at Mesopause. This inversion of temperature is probably due to absence of ozone molecules beyond the stratosphere. This layer extends to 80 km. above the’earth.
4. Thermosphere : It lies above the Mesosphere and is divided into two parts-the Ionosphere and Exosphere.
1. Ionosphere : The air layer lying behind the stratosphere is known as the Ionosphere. This extends to a height of 80 km to 480 km. Radio waves used in long distance radio communication are reflected back to earth by Ionosphere. In this way, radio massages can be transmitted round the curve of the Earth. This is about 970 km thick.
2 Exosphere : The upper-most layer of the atmosphere is called Exosphere. It lies somewhere between 480 km. and above the Earth. It is known only to aerospaceships.
