The atmosphere is a mixture of several gases nitrogen being predominant. The atmosphere also contains oxygen which is vital to all livingcreatures. It also contains dust particles which help in the formation of rain drops. We are protected from the ultra-violet rays emitted by the sun by the ozone layer

The atmosphere extends to nearly 1600kms from the surface of the earth. It is dense near the surface. The density of air decreases as we go further up from the surface of the earth. Theatmosphere is divided into five parallel zonesThey are ;1. Troposphere 2. Stratosphere 3. Mesosphere 4. Thermosphere 5. Exosphere

This is the lowest layer of the atmosphere withan average height of 12km. In this layer, thetemperature decreases at the rate of 10c forEvery 165meter. This is called the ‘lapse rate’it is due to this phenomenon that the mountain peaks always remains cool. Clouds, fog, snowfall, and rainfall occur in this layer

The stratosphere lies above the troposphere and extends up to 50kms from the earth’s surface .Temperature is almost constant in this layer.

Thermosphere extends from 90-500kms. Due to the intense heat, oxygen and nitrogen atoms get ionised.Due to ions, radio waves get reflected to the earth. As a result of this, one can watch T.V and listen to radio. Mobile co- mmunication is also possible because of this layer.Due to the presence of ions it is also called IONOSPHERE.

The exosphere is also known as the magnetosphere. It is the outer most layer of the atmosphere.it contains only traces of atmospheric gases.

The sun is very chief source of heat. The earth is about 150 million kms from the sun, and hence the earth receives little insolation. About 37% of sun’s energy is lost by reflection from the clouds and dust particles. Another 6% is absorbed directly by the gases in the upper atmosphere. Thus the remaining 57% reaches the earth.

Based on the solar radiation, the surface of the earth can be divided into 3 different zones: 1) Torrid zone

2)temperate zone3)frigid zone

The torrid zone extends on both side of the equator up to the tropic of cancer in the north and tropic of Capricorn in the south. This is the hottest zone . Mild winter are its feature. Hence the Greeks described this zone as ‘Winterless tropics’.

This zone extends from 23.5dc to 66.5dc in both the hemisphere. Warm summer and cold winter are its marked feature. It is also known as an intermediary zone.

The frigid zone extends from 66.5 to 90 on both sides of the equator.This zone is characterized by mild and short summer long and