Structure and Composition of Atmosphere

The atmosphere is a layer of gases containing numerous small-suspended solid and liquid particles surrounding the earth. It has no outer boundary, it just fades into space. The dense part of the atmosphere lies within 30km above the earth's surface.

The atmosphere is divided into regions based on its thermal characteristics (temperature changes), chemical composition, movement and density.

It is divided into five regions, which are:

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

The composition of the atmosphere

Troposphere

This is the region nearest to the earth's surface which extends to an altitude up to 10 km above the poles and 20km above the equator. It is the most dense part of the atmosphere(80% by mass of the atmosphere) which contains most of the atmosphere's water vapour.

Stratosphere

It starts from the tropopause and extends to 50km high. It is more stable, drier and less dense composed to troposphere.

The temperature slowly increases with altitude due to the presence of ozone layer, which absorbs ultraviolet rays from the sun. The ozone layer lies in the middle of the stratosphere between 20 and 30km. Ozone is triatomic (three-molecules) form of oxygen.

Advantages of stratosphere

1. It absorbs the ultraviolet radiations, which would otherwise reach the earth's surface, which is harmful to both plants and animals.
2. It prevents large storms from extending much beyond the troposphere due to its stability. Mesosphere

Thermosphere

It is just above the mesopause and extends up to 690km high. The temperature increases with altitude due to the sun's heat. The temperature in this region can go as high as1727°C and chemical reactions occur faster in this region than on the earth's surface.

This layer is also known as the upper atmosphere. The lower part of the thermosphere, from 80 to 550km above the earth's surface, contains the ionosphere. This is a region containing a high concentration of charged particles called ions and free electrons.

Importance of ionosphere

The large number of free electrons in the ionosphere allows the propagation of electromagnetic waves. It absorbs the dangerous radiations like X-rays and extreme ultraviolet (EUV) radiation. It plays an important role in commination of radio waves.

Exosphere

Is the outermost region of the atmosphere. In this region, the atmospheric gas pressure is very low such that light atoms such as hydrogen and helium may acquire sufficient energy to escape the earth's gravitational pull.

The upper part of the exosphere is called magnetosphere. The motion of ions in this region is strongly constrained by the presence of the earth's magnetic field. This is the region where satellites orbit the earth

The importance of various layers of the atmosphere

The importance of the atmosphere include the following:

1. The troposphere controls the climate and ultimately determines the quality of life on the earth.
2. The troposphere is important for life on earth. The layer contains gases which include oxygen which is used for respiration by animals and carbon dioxide which is used by plants in photosynthesis. The nitrogen found in this layer also provides an inactive environment for many chemical processes to take place.
3. The stratosphere prevents harmful ultraviolet radiation from reaching the earth.
4. The mesosphere, thermosphere and exosphere also prevent harmful radiation such as cosmic rays from reaching the earth's surface.
5. Communication is also made possible by some layers of the atmosphere, specifically the ionosphere.