How the presence of life on Earth brought about environmental change

How the presence of life on Earth brought about environmental change

1. ATMOSPHERIC OXYGEN

   • Oxygen is a reactive element, concentration declined when it reacted with other elements eg) oxidation weathering
   • Continued presence of oxygen in atmosphere relies on processes that replace it as other processes remove it
   • Small amount of oxygen released by photolysis of water and photosynthetic bacteria
     • Oxygen absorbed UV light from sun, oxygen molecules then split, produced monatomic oxygen which reacts with diatomic oxygen to produce O3/Ozone
       • Allowed ozone layer to form, provided protection from UV light to living organisms.
         • Before this abundant life not possible so early organisms lived in oceans where water protected them from UV light

2. ATMOSPHERIC CARBON DIOXIDE

   • Naturally released into atmosphere by volcanoes
   • Essential greenhouse gas, helps maintain heat in atmosphere, without it Earth would be too cold to sustain life
   • Excessive CO2 levels would cause temperatures to rise too high for life to survive
   • Light output of the sun increases by 10% every billion years so 30% brighter than when life first developed
   • Living organisms helped maintain suitable atmospheric temperatures by removing CO2 (photosynthesis) and storing in fossil fuels and carbonate rocks (chalk/limestone)

3. THE HYDROLOGICAL CYCLE

   • Heat energy from absorbed sunlight causes water in the sea to evaporate
   • May be carried over land where it falls as rain then flows back to sea
   • 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
   • Transpiration from leaves is unavoidable as the stomata must open for gas exchange