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What is Atmosphere? How it is developed and what are the layers of the atmosphere

  The atmosphere is the envelope of air that surrounded the surface of our earth. It is held near the earth due to its strong gravitational force of attraction. It is impossible for today's science to know about the exact height from where the atmosphere extends. This area is known as the Atmospheric boundary. The atmosphere is densest at sea level. This atmosphere provides us oxygen, shelter from the ultraviolet radiation, conditions for evolution, etc.

    On the basis of temperature, Earth atmosphere can be divided into five major layers-






1)      Troposphere: It is the lowermost layer of our earth’s atmosphere. It is also known as the innermost layer of our atmosphere. Starting from the ground level, it extends upward to about 10 km above the sea level. This layer basically consists of 78% of nitrogen, 21% of oxygen and 1% of argon, carbon dioxide, water vapor, etc. This layer gives more oxygen to animal and plant kingdom for survival and evolution on earth. Most of the clouds form in this layer because 99% of water vapor is found in this layer. 75% of atmospheric air also found in this layer. The entire weather phenomenon (hurricane, thunderstorm, rain, snow, cyclone etc.) occurs in this layer. The greenhouse effect, water cycle or the water exchange between the earth and the atmosphere also occurs in this layer. The boundary between the stratosphere and the troposphere is called Tropopause. The temperature decrease in this layer with height due to decrease of density. In this layer, the average temperature on the ground floor is 17 degree Celsius and at the Tropopause it decreases about -51 degree Celsius. The thickness of Tropopause varies from about 7 to 8 km at the poles to about 16 to 18 km at the equator.

 

2)      Stratosphere: it is the second lowermost layer of our earth atmosphere. It extends upward to about 50 km from the Tropopause. Due to less disturbances of weather phenomena, most of commercial jets fly in this layer. This layer contains 90% of ozone layer, which protects us from the ultra violet radiation. The temperature of this layer increases with increase in height due to absorption of ultra violet radiation by ozone layer. The temperature increases with height is 6.5 degree Celsius per km. the average temperature at top of the stratosphere is about -15 degree Celsius. The boundary between the stratosphere and mesosphere is called Stratopause. The thickness of Stratopause is about 45-50 km near the mesosphere.

 

3)      Mesosphere: Mesosphere lies between the thermosphere and stratosphere. It is a very cold region, which extends upward to about 80 km from the surface of earth. At a height of 60 km there is an intermediate layer, which is known as radio wave absorbing layer. An important feature of this layer is that this layer is higher temperature in winter as compare to the summer season, which is apparently due to small ozone content. Most of the meteors are vaporized and burned in this layer. As a result, enables the destruction of meteors before it can damage all the living things on earth.  The average temperature of this layer at the bottom is -15 degree Celsius and at the top of it is -101 degree Celsius. The boundary between the thermosphere and the mesosphere is known as Mesopause.

 

4)      Ionosphere: ionosphere is located between the thermosphere and the exosphere. It is a region of electrically charged and ionized air. It extends upward to about 150 km from the surface of earth. A part of ionosphere lying between 800 km is known as thermosphere which is characterized by a steady rise in temperature. It protects us from falling meteorites. Radio waves are reflected by this layer. The phenomenon Aurora borealis also occur in this layer.

 

5)      Exosphere: Above the ionosphere lies the exosphere. It is the outermost zone of the atmosphere. It is also known as diffusion zone where the atmospheric gases defused into the open space. Its boundaries are not known. Although the exosphere is the most distance layer of earth’s atmosphere, it is the layer that is the planets first layer of defense against the sun’s rays. It is also the first layer to come into contact and protect the earth from meteors, asteroids and cosmic rays.

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