danielravennest t1_j1eo26p wrote
Reply to comment by allegedly-insane in Mars' ancient atmosphere may not have had much oxygen after all by pecika
It isn't a niche in terms of energy flow. Green plants figured out how to extract solar energy, which is a more abundant source than chemical energy like that found in black smokers. The waste product of photosynthesis is oxygen. Once all the oxidizable minerals were used up, it accumulated. Critters then learned to use it as an energy source.
allegedly-insane t1_j1fo9ls wrote
I thought it was bacteria that caused the oxygenation event. Was it plants?
danielravennest t1_j1igs5v wrote
Cyanobacteria are much older than regular plants. At some point they were absorbed and became the chloroplasts of modern plant cells. At first cyanobacteria could not tolerate oxygen themselves, and what was disposed as a waste product was oxidized with iron, forming the "banded iron formations", a modern iron ore source. So there wasn't enough free oxygen to accumulate in the atmosphere.
Free-range bacteria don't fill all the ocean area they inhabit. Once the oxygen sinks like iron were full, and they were concentrated in plant cells that could tolerate oxygen, the oxygen production grew by a large amount, and significant build up could happen,
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