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External Structure of the Earth

Answer Text:
a) The Atmosphere
• Layer of gases surrounding the earth.
• The earth revolves with it because it’s held onto it by gravity
• It’s about 330km thick. Composition of the Atmosphere
a) Gases-exist as a mixture
b) Smoke particles
c) Dust particles
d) Water vapour
The structure of the Atmosphere It’s divided into 4 layers/zones namely:
1. Troposphere
-Lowest layer of the atmosphere
Contains 90% of water vapour
- Rainfall is got from it
- Temperature decreases with increase in altitude (lapse rate)
- Air is turbulent due to mixing of air
- Contains dust particles there is a zone of transition between troposphere and stratosphere called tropopause.
2. Stratosphere/ozonosphere
- Layer lying next to troposphere
- Has layers
- Lower isothermal layer in which temperature is constant
- Upper layer of temperature inversion in which temperature
increases with increasing altitude
- Has ozone layer which absorbs harmful ultraviolet radiation.
- Air is calm so it is used by passenger jets
- Limited amounts of water vapour
- There is a zone of transition between stratosphere and mesosphere called stratopause.
3. Mesosphere
- Middle layer of the atmosphere.
- Temperature decreases with increasing altitude.
- There is a zone of transition between mesosphere and thermosphere called mesopause which is an inversion layer.
4. Thermosphere/ionosphere
• High radiation is present.
• The pressure is very low.
• Gases and molecules in this layer exist as ions due to high radiation.
• Has no definite top but merges gradually into the outermost part of the atmosphere called exosphere.
• Exosphere consists of rare gases like hydrogen and helium.
• Beyond the atmosphere there is the outer space.
• Outer space is the universe beyond the atmosphere in which other planets and stars exist