A cover of gases surrounding the earth is called the earth’s atmosphere or simply as atmosphere. Atmosphere extends from the earth’s surface to about 1000km. But about 99% of the atmospheric air is present without 40 km from the earth’s surface. The main layers of atmosphere, from the surface of the earth upwards, are:

  1. Troposphere
  2. Stratosphere
  3. Mesosphere
  4. Thermosphere

Most of the atmospheric air is present in Troposphere. Troposphere mainly consists of nitrogen (78.1%), oxygen (21%), carbon dioxide (0.03%) and water vapor. The thickness of Troposphere changes from about 8km over the poles to about 16 km over the Equator.

In Stratosphere, there is very little water vapor. Supersonic aircraft fly in this region. The temperature in Stratosphere is higher than that in Troposphere. This is rich in ozone gas forming an ozone layer. In Mesosphere, the temperature gradually falls to reach -85°C atomic about 80 km above the earth where Thermosphere begins.