Atmosphere – The region of air is found around of earth is called as the atmosphere of the earth. The presence of air above the surface of the earth is its gaseous component that forms an invisible cover around the earth.

The atmosphere extends to a height of about 40 kilometers from the surface of the earth. About 99 percent of air is present in this region through traces of air have been found above the height of 100 kilometers. The density of air is the highest near the sea-level and if we go higher above the sea-level, the density of air goes on reducing. The composition of air also changes with the change in height. There are some of the concentric layers in the vertical profile of the atmosphere.

The four main layers of the atmosphere are

• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere

Most of the atmospheric air is present in the troposphere.

Role of atmosphere – The atmosphere protects the living things from harmful radiations such as ultraviolet rays by forming an ozone layer in which Ozone is a gas whose one molecule contains three atoms of oxygen with the molecular formula of Ozone is O₃. Ozone is formed by the action of sun-rays on the atmospheric oxygen and situated at a height of about 16 kilometers from the earth, the sun-rays convert the oxygen present into ozone.

The amount of ozone gas in the atmosphere increases up to a height of around 23 kilometers. In fact, the ozone layer is the thickest at the height of 23 kilometers in the atmosphere. The ozone layer is present in the stratosphere region of the atmosphere and consists mainly of ozone gas.