Atmosphere: Introduction and Structure

  • The earth is surrounded by a thick layer of air. This thick layer of air is called the atmosphere.
  • The thick layer of air that surrounds the earth’s crust is called atmosphere.
  • The biosphere of the earth consists of three different spheres, which are: hydrosphere, lithosphere and atmosphere.
  • The atmosphere consists of different types of gases like nitrogen, oxygen, carbon dioxide, neon, argon, etc.
  • It also consists of water vapour and dust particles.
  • The atmosphere covers the lithosphere and hydrosphere of the earth in the form of canopy.
  • Therefore, atmosphere is the canopy of air around the earth.
  • The air present in the atmosphere keeps on moving due to the effect of the earth’s gravity.

Structure of Atmosphere

  • As the altitude increases, the layer of atmosphere becomes thinner, and then temperature also varies at different heights.
  • According to the altitude and temperature, the atmosphere is divided into five different layers. They are as follows:

Atmosphere: Composition and Structure - PCSSTUDIES - Geography

                                                                                  Image source: pcsstudies

A) Troposphere

  • It is the lowermost layer of the atmosphere which extends up-to 16 km from the surface of the earth.
  • It contains a large amount of heavy gases like nitrogen, oxygen, carbon dioxide, inert gases, water vapour, dust particles, etc.
  • Various activities related to the weather like cloud formation, wind, light, rain, hail stone, lightning, fog formation, etc. take place in this layer.
  • Therefore, the troposphere is very important for meteorologists.
  • Scientists forecast the weather by studying this layer.
  • The temperature of the troposphere changes according to the height.
  • So, this layer is also called a variable layer.
  • There is a fall of about 6.50C in temperature in this layer per kilometer increase in altitude.
  • The troposphere is thinner at the poles. About 95% of atmosphere lies in the troposphere.
  • The uppermost part of this layer is called the tropopause.
  • It separates the troposphere and stratosphere. It has about -560C temperature.
  • This layer lies at about 8 to 10 km from the poles and about 16 km from the equator.


B) Stratosphere

  • It is the second layer of the atmosphere located between the troposphere and mesosphere.
  • This layer extends from 16 km to 50 km vertically upward from the earth’s surface.
  • The stratosphere consists of the ozone layer at its upper surface. So it is also called ozonosphere.
  • The ozone layer is formed and destroyed at about 20-25km upwards in the presence of solar radiation.
  • The ozone absorbs most of the solar radiations and stops it from entering the earth which creates favourable condition for living beings of the earth.
  • In the stratosphere the temperature increases from -56oc to -2oc as the height increases.
  • The temperature of lower layer of stratosphere is about -53oc .This layer contains thin cloud.
  • There is negligible amount of humidity in this layer. The uppermost boundary of this layer is called the stratospause.
  • It separates stratosphere and mesosphere.

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C) Mesosphere

  • It is the third layer of atmosphere located between the stratosphere and thermosphere.
  • It extends from out altitude of 50km to 80 km above the earth’s surface.
  • The temperature of mesosphere decreases with increase in height.
  • The temperature of this layer varies from -2oc to -109oc with increase in height.
  • In the mesosphere strong wind blows from west to the east during winter and from the east to the west during spring season.
  • The streaks of hot gases released from meteors can be seen in this layer.
  • This layer does not determine climate and weather.
  • The upper most boundary of mesosphere is called mesopause.
  • It separates the mesosphere and thermosphere. The temperature of the mesosphere is about -109oc during summer.


D) Thermosphere

  • It is the layer of atmosphere located between the mesosphere and exosphere.
  • It extends from 80km to 720km vertically upward from the earth’s surface.
  • This sphere occupies about 0.01% of the total region of the atmosphere.
  • The lower region of thermosphere contains ions of nitrogen, oxygen etc.
  • The gases molecules like nitrogen, oxygen etc. under go ionization and give ions due to the effect of UV radiation of the Sun.
  • Therefore, thermosphere is also called the ionosphere. In this layer, there is very high temperature due to the effect of the solar radiation.
  • The upper region of the thermosphere mainly contains hydrogen and helium.


E) Exosphere

  • It is the outermost layer of the atmosphere which extends beyond the thermosphere.
  • The temperature of this layer is very high i.e. about 1200oc to 6000oc.
  • In exosphere, the density of air is very low, but the wind blows at high speed.
  • This layer is very far from the earth’s surface so there is no effect of gravity.
  • The exosphere mainly contains hydrogen and helium.
  • The exosphere forms the outermost edge of the atmosphere. So, it is also called the fringe region.




Atmosphere: Introduction and Structure