Atmospheric Layers and Composition

  • The envelope of air that completely surrounds our earth is known as atmosphere. Atmosphere extends to about 1000 km above the earth. 99% of the total mass of atmosphere is found within 32 km.
  • The main constituents of air are nitrogen, oxygen, carbon dioxide, argon, helium, ozone, hydrogen, and dust particles.
  • The main gases present in the atmosphere are nitrogen (78%) and oxygen (21%).
  • Carbon dioxide, argon, hydrogen, dust particles, water vapour, etc., comprise the remaining 1%.
  • The different layers of atmosphere are troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
  • Troposphere is the first and the most important layer of atmosphere. Tropopause is the border between troposphere and stratosphere.
  • Stratosphere lies above the troposphere. This layer is free from clouds and associated weather phenomenon. Stratopause divides stratosphere from mesosphere.
  • Mesosphere is the third layer of atmosphere and lies above the stratosphere. On entering from the space, meteorites burn up in this layer.
  • Thermosphere extends up to a height of 90 km from the earth’s surface. Ionosphere is a part of this layer.
  • Exosphere extends beyond thermosphere up to a height of 960 km from the earth’s surface.
  • Atmosphere protects us by not allowing harmful radiations from sun reach the surface of earth.
  • Carbon dioxide and water vapour absorb the heat radiated from earth’s surface. Greenhouse effect is the natural process by which the atmosphere traps some of sun's energy and warms the earth enough to support life.
  • Solar radiation is the only primary source of heat and light for our earth. The earth and its atmosphere get heated by insolation. Insolation is the incoming solar energy intercepted by earth. A considerable amount of insolation is reflected back into the atmosphere. Atmosphere absorbs only 14% of the incoming insolation.
  • Terrestrial radiation is the sun’s energy absorbed by earth’s surface and radiated out into the space.
  • Atmosphere is heated more by terrestrial radiation given out by earth than by incoming insolation.

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