EXTERNAL STRUCTURE OF THE EARTH
- 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:
- 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.
- 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’s used by passenger jets
- Limited amounts of water vapour
- There is a zone of transition between stratosphere and mesosphere called stratopause.
- 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.
- 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.
Significance of Atmosphere
- a) Animals and plants breathe in from it oxygen for respiration.
- b) Plants use carbon dioxide from it for photosynthesis.
- c) Water vapour in the atmosphere condenses to form clouds which give us rain.
- d) Ozone layer in the stratosphere shields us from ultraviolet radiation which may cause cancers.
- e) Carbon dioxide and methane in the atmosphere cause global warming through the green house effect.
- b) The Hydrosphere
- Part of the earth’s surface covered by water masses e.g. oceans, seas, lakes, rivers and even underground water.
- It comprises 73% of the earth’s surface area.
- The atmosphere and hydrosphere are related in that atmospheric gases penetrate to the ocean depth in solution form.
• The lower atmosphere, hydrosphere and the upper part of the earths crust are called biosphere meaning the sphere of the earth in which organic life exists
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