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| Question | Answer |
| Step 1 | Volcanic activity releases: CO2 Methane Ammonia Water vapour |
| Step 2 | Water vapour condenses to form oceans. |
| Step 3 | Green plants evolve to take in CO2 and breathe out O2. |
| Step 4 | Carbon becomes locked up in sedimentary rocks as carbonates and fossil fuels. |
| Step 5 | Methane and ammonia react with O2, and nitrogen is released (nitrogen also occurs as a result of dentrifying bacteria on nitrates of decaying plants) |
| Step 6 | Some of O2 is converted into ozone. Ozone layer blocks out harmful UV rays. |
| Step 7 | This allows for the development of new life. Plants & algae produced O2 that's now in atmosphere. |
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