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The percentage of clear air is...

78% - Nitrogen 

21% - Oxygen

0.035% - CO  , noble gases e.g. argon

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Carbon Cycle

- Combustion of fossil fuels which increases the level of carbon dioxide and decreases the level of oxygen.

- Respiration by humans and animals which increases the level of carbon dioxide and decreases the level of oxygen.

- Photosynthesis by plants increases the level of oxygen and decreases the level of carbon dioxide.

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How the atmosphere evolved

Phase 1 - Volcanoes gave out steam and CO  

Phase 2 - Green plants evolved and produced oxygen

Phase 3 - Ozone layer allows evolution of complex animals (Ozone layer - O  )

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Catalytic converters

Car exhaust systems have catalytic converters. These convert carbon monoxide into carbon dioxide:

carbon monoxide + nitrogen oxide → nitrogen + carbon dioxide

2CO + 2NO → N2 + 2CO2

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Human effects on air composition

Deforistation - more rainforests are cut down so less photosynthesis.

Increased population - the worlds energy requirements increase

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Theory of atmospheric evolution

Water vapour went down because:

  • as the Earth cooled down, most of the water vapour condensed and formed the oceans.

Carbon dioxide went down because:

  • it was absorbed by plants during photosynthesis
  • it was locked up in fossil fuels
  • it dissolved in the oceans.

Nitrogen went up because:

  • it is not very reactive and, once formed, it is not easily removed from the atmosphere again.

Oxygen went up because:

  • it was released by plants during photosynthesis
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