Topic 1

Early atmosphere contained large amounts of carbon dioxide & water vapour - released from volcanoes - contained almost no O2

Different sources do not allow us to be precise about the E.A - assumptions have been made, but help form a general idea

Water vapour from volcanoes condensed forming oceans - accumulation of water droplets

Carbon dioxide reduced by:
- dissolution (CO2 reacting with accumulated water)
- dissolved into marine organisms > formed carbonate rocks
- Carbon dioxide used by plants for photosynthesis > reduced by more photosynthesising organisms evolved > releasing and increasing amount of oxygen

Current comp. Nitrogen 78%, Oxygen 21% argon 0.9%, carbon 0.04%, others traces
Changes caused by volcanic activity and human activity