Atmosphere

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2. Atmosphere

  • The atmosphere is the thin blanket of air around the earth that consists of various gases. The atmosphere is held by the earth due to its gravitational pull. The most important layer of the atmosphere is the area that extends up to 120km from the surface of the earth. 50% of the total air content of the atmosphere is present in the region that extends up to 5-6km from the earth’s surface. (David Waugh-2000) 


  • The atmosphere is immensely important for the existence of living beings and plant life as it provides oxygen for respiration of living beings and the necessary carbon dioxide for the process of Photosynthesis.






  • The atmosphere mainly consists of various gases, and it also contains water vapor, dust and salt particles.






  • As a result of different human activities and natural phenomena (Exhaustion of gases during volcano eruptions, release of methane from marshes etc.) natural gases like Carbon Dioxide, Methane, Carbon Monoxide and Sulphur Dioxide are added to the atmosphere. This changes the composition of the lithosphere and may adversely affect the existence of life.
 


Structure of the atmosphere.




  • The atmosphere has five distinct layers that are determined by the changes in temperature that happen with increasing altitude. Layers of Earth’s atmosphere is divided into five different layers as:


1.Troposphere

2.Stratosphere

3.Mesosphere
   
    4.Thermosphere










1.Troposphere


  • The troposphere is the lowest layer in the atmosphere. It extends upward to about 10 km above sea level starting from ground level. The lowest part of the troposphere is called the boundary layer, and the topmost layer is called the tropopause. The troposphere contains 75% of all air in the atmosphere. Most clouds appear in this layer because 99% of the water vapor in the atmosphere is found here. Temperature and air pressure drop as you go higher in the troposphere. When a parcel of air moves upwards it expands. When air expands it cools. Due to this reason, the base of the troposphere is warmer than its base because the air in the surface of the Earth absorbs the sun’s energy, gets heated up and moves upward as a result of which it cools down.



2.Stratosphere



  • The stratosphere lies above the troposphere lies the stratosphere which extends from the top of the troposphere to about 50 km above the ground. The ozone layer lies within the stratosphere. Ozone molecules in this layer absorb high-energy ultraviolet (UV) light from the Sun and convert it into heat. Because of this, unlike the troposphere, the stratosphere gets warmer the higher you go! 




3.Mesosphere



  • The mesosphere is the third layer of the atmosphere. It spans a vertical distance from 50 to 90 km. The temperature in the mesosphere grows colder with the altitude. This is because there are few gas molecules in the mesosphere to absorb the Sun’s radiation. The only heat source is the stratosphere below. The mesosphere is extremely cold, especially at the top, dropping to a temperature as low as -90°C. An astronaut travelling through the mesosphere would experience severe burns from the sun’s ultraviolet light because the ozone layer that provides UV protection is in the stratosphere below. Meteorites burn in this layer on entering the atmosphere from outer space.



4.Thermosphere



  • One of the outermost layers is the thermosphere. The definition of thermosphere is the layer of the atmosphere that stretches from about 90 km to between 500 and 1,000 km above the Earth's surface. It is between the mesosphere and exosphere which is the outermost layer that fades into outer space. The temperature increases rapidly with the altitude.  There is a high temperature in this layer. The temperature at noon is about 11000 C. The difference between the temperature of day and night is at a higher level.  The volume of gases is very low.  The upper boundary of the thermosphere is the upper boundary of the earth's atmosphere.




































                                                                                                     

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