An atmosphere is the layer of gases which surrounds the body of a sufficient mass and which is also held in the correct place by the gravity. Likewise, the atmosphere of Earth is a layer of gas which surrounds the Earth and it is retained by the gravity of the Earth. The atmosphere helps to protect produce life on the earth by absorbing the ultraviolet radiation of the sun, by reducing the temperature between night and day and by warming up the surface of the earth by the heat retention process.
An atmospheric stratification explains the atmosphere’s structure in a better way by dividing the atmosphere into various layers with certain characteristics like composition or temperature. The mass of the atmosphere of the earth is about 5×1018 kg, With the increase of altitudes, the atmosphere gets thinner, with no clear outer limit between the outer space and the earth. Often, the Kármán line is known as the boundary between the outer space and the atmosphere.
Composition of the Atmosphere:
The atmosphere of earth is often known as the air and it is used in photosynthesis and breathing. The dry air consists of 78.09% nitrogen gas, 20.95% oxygen gas, 0.93% argon gas, 0.039% carbon dioxide gas, and little amounts of other gases. These gases are known as trace gases or greenhouse gases. It includes: carbon dioxide, nitrous oxide, methane,and ozone. The air also consists of some amount of water vapor. Apart from that, various chemical and natural substances like pollen, dust, spores, volcanic ash, and sea spray can be present in the sample of the unfiltered air
Air is very much essential for the survival of the terrestrial animals and terrestrial plants found in the troposphere of the Earth.
Structure of the Atmosphere:
The structure of the atmosphere can be divided into five basic layers, located from lowest to the highest. These are:
· Troposphere- This layer of the atmosphere starts from the surface and spreads up to 9 km at the poles and 17km at the equator. The layer gathers heat by transferring the energy from the surface. So, this layer is very warm.
· Stratosphere- The layer stratosphere expands from tropopause about 51 km. In this layer, the temperature increases with the increase of height.
· Mesosphere- Mesosphere expands from Stratopause to 80 or 85 km. In this layer, the temperature decreases with the increase of the height. The boundary of the mesosphere, which is known as mesopause is said to be the coldest place on Earth.
· Thermosphere- In this layer of the atmosphere, the temperature increases with the increase of the height. Due to the low density of molecules, International Space Station is situated in this layer.
· Exosphere- It is the utmost layer of the atmosphere of the Earth. This layer consists of helium and hydrogen.