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Two billion years ago, snowball Earth was defrosted in huge asteroid crash – and it's been downhill ever since

Muscleguy

Like happened as a result of those pesky blue-green bacteria who at the time were busy using this new fangled photosynthesis thing with the side effect of burping out toxic oxygen. Pretty well every other sort of life (bacteria and archaea) were anaerobes.

It is thought that the mitochondria in our cells and in every other non Prokaryote (bacteria and archaea) to make the first Eukaryotic cell happened when a large, nucleated bacterium (probably an archaea) tried to engulf and eat some small bacteria who could do oxygen chemistry and failed to digest them.

Even now pretty much ALL of the oxygen chemistry in our cells is done safely inside the double membrane of the mitochondria and the rest of the cell is still anaerobic.

Those blue-green bacteria? still around of course but an early Eukaryotic cell (think amoeba) did the 'engulf bacteria and fail to digest them' thing with those and became plants. After all lying around in the sunlight letting the lodgers make your food sure beats trying to eat things for a living. Not that there aren't freeloading parasitic plants going one better of course.

There's a layer of, essentially rust in the really old rocks. Oxygen levels couldn't rise appreciably in the atmosphere or oceans because all the reduced metals, especially iron had to be saturated with oxygen (rusted) and stop being oxygen sponges. The early Earth had a reducing atmosphere. It was very different from now.

It's thought the oxygen contributed to the global cooling and snowball earth.

Life: futzing with planetary chemistry for billions of years. It seems hominids have been causing global warming and extinctions for a couple of million years. H. erectus made fires for a start and our distant ancestors might have kicked predators like sabre toothed cats off their kills causing their extinction. Even today lions have to put up with landrovers filled with hominids gawping at them while they eat.

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