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allegedly-insane t1_j1bi8xa wrote

Reply to comment by cosmiccoffee9 in Mars' ancient atmosphere may not have had much oxygen after all by pecika

Not necessarily, oxygen is considered extremely toxic for life. Our very niche form of life is aerobic.

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Autisonm t1_j1btk9k wrote

So basically we're those aliens that breath in toxins through respirators to survive in sci-fi movies?

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allegedly-insane t1_j1bvvqr wrote

Meh, complex life as far as we can tell is because of oxygen. If there are aliens out there, they're most likely susceptible to oxygen toxicity but they're also brainless anaerobic single-cellular life forms.

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Underhill42 t1_j1fac9w wrote

Define complex life. The Earth was teeming with multicellular plants and animals long before the Great Oxygenation Event. The Cambrian Explosion didn't happen until much later, but there's not really any evidence that there was any sort of causal connection between the two. Not with hundreds of thousands of years of near-steady ocean oxygen levels between the two.

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cosmiccoffee9 t1_j1bl6jr wrote

yes, "quasi-spacefaring Earth-based species" is a fairly narrow niche, fair enough.

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allegedly-insane t1_j1bvjuq wrote

It really is as far as we can tell. It's much more likely that anaerobic (glucose based, not oxygen) life exists than aerobic. Many reasons for this include it's easier (doesn't require a ton of oxygen), less dangerous environments (not exposed to open-air), and as far as we know is the precursor to aerobic life. Anaerobic organisms, before anti-bacterials, were extremely successful little survivors :)

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Vindaloovians t1_j1brnpc wrote

Toxic perhaps, but oxygen also allows for a lot more availability of energy (aerobic vs anaerobic respiration). It's possible that complex life developed as a consequence of increased atmospheric oxygen.

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danielravennest t1_j1eo26p wrote

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.

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allegedly-insane t1_j1fo9ls wrote

I thought it was bacteria that caused the oxygenation event. Was it plants?

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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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jawshoeaw t1_j1c3u7d wrote

It’s not “extremely toxic” unless you don’t have the biochemistry to deal with it.

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allegedly-insane t1_j1cgsrd wrote

Oxygen is extremely toxic. Both to humans and especially anaerobic life forms. Having the biochemistry to deal with low concentration of oxygen doesn't really mean much — it's like saying mercury isn't toxic if you have the biochemistry to deal with it.

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