The percentage of clear air is...
78% - Nitrogen
21% - Oxygen
0.035% - CO , noble gases e.g. argon
- 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.
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 )
Car exhaust systems have catalytic converters. These convert carbon monoxide into carbon dioxide:
carbon monoxide + nitrogen oxide → nitrogen + carbon dioxide
2CO + 2NO → N2 + 2CO2
Human effects on air composition
Deforistation - more rainforests are cut down so less photosynthesis.
Increased population - the worlds energy requirements increase
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