Practice question · Put in order
Arrange these events in the order they occurred in Earth’s history.
- An ozone layer forms and shields the land surface
- The Great Oxidation Event transforms the atmosphere
- Oxygenic photosynthesis begins releasing free oxygen
- Anoxygenic photosynthesis evolves in early bacteria
- Life colonises the land
Hints
- Oxygen must accumulate before ozone can form from it.
- Land could not be colonised until UV was screened out.
Show the answer
- Anoxygenic photosynthesis evolves in early bacteria
- Oxygenic photosynthesis begins releasing free oxygen
- The Great Oxidation Event transforms the atmosphere
- An ozone layer forms and shields the land surface
- Life colonises the land
Why
Photosynthesis came first, oxygen accumulated, ozone formed from that oxygen, and only then could life leave the water. The colonisation of land was gated by a by-product of a metabolic pathway, a striking case of biology changing its own planet.
Practise Photosynthesis and the Oxygen Revolution
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