How the presence of life on Earth brought about environmental change

ATMOSPHERIC OXYGEN
1. Oxygen is a reactive element, concentration declined when it reacted with other elements eg) oxidation weathering
2. Continued presence of oxygen in atmosphere relies on processes that replace it as other processes remove it
3. Small amount of oxygen released by photolysis of water and photosynthetic bacteria
  1. Oxygen absorbed UV light from sun, oxygen molecules then split, produced monatomic oxygen which reacts with diatomic oxygen to produce O3/Ozone
    1. Allowed ozone layer to form, provided protection from UV light to living organisms.
      1. Before this abundant life not possible so early organisms lived in oceans where water protected them from UV light
ATMOSPHERIC CARBON DIOXIDE
1. Naturally released into atmosphere by volcanoes
2. Essential greenhouse gas, helps maintain heat in atmosphere, without it Earth would be too cold to sustain life
3. Excessive CO2 levels would cause temperatures to rise too high for life to survive
4. Light output of the sun increases by 10% every billion years so 30% brighter than when life first developed
5. Living organisms helped maintain suitable atmospheric temperatures by removing CO2 (photosynthesis) and storing in fossil fuels and carbonate rocks (chalk/limestone)
THE HYDROLOGICAL CYCLE
1. Heat energy from absorbed sunlight causes water in the sea to evaporate
2. May be carried over land where it falls as rain then flows back to sea
3. Most rain falls relatively close to the coast but transpiration by plants returns water vapour to the atmosphere so it can be blown further inland
4. Transpiration from leaves is unavoidable as the stomata must open for gas exchange

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How the presence of life on Earth brought about environmental change

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