Stable free oxygen on non-life planet

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jseah
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Stable free oxygen on non-life planet

Postby jseah » Sun May 13, 2018 5:23 am UTC

So it's commonly stated that free oxygen is unstable in an atmosphere and will react with things. I wonder if it is possible to have everything already reacted with oxygen such that free oxygen remains stable because there's nothing to react.

eg. what might happen in the long term if free oxygen was continually provided without reductive processes. The scenario is something like this:

> Earth-like planet within liquid water zone, no life arose
> By magic, ROB or aliens, the atmosphere is constantly transmuted to have at least 25% O2, converting other molecules to oxygen on a mass-equivalent basis
> If the atmosphere is <1 atm in pressure, O2 is added until it has 1 atm, material from the core will be transmuted to oxygen on a mass-equivalent basis
> All other processes, like geology and oceans, proceed as normal

Forward a couple of million years and everything that can be oxidized will have been oxidized. If the O2 maintenance is removed, will the oxygen then disappear?
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Eebster the Great
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Re: Stable free oxygen on non-life planet

Postby Eebster the Great » Sun May 13, 2018 2:18 pm UTC

Yes, and you don't need to make it that extreme. It is hypothetically possible for reducing chemicals on the surface to be limiting rather than atmospheric oxygen. Because the density of air is so low and the thickness of any plausible atmosphere so much thinner than the thickness of the crust, this might be unlikely. But on a planetary body with a thick atmosphere but no crustal movement, it might be possible, especially if UV rays in the upper atmosphere continually produce O2 and H2 from H2O. It will run out of free oxygen *eventually*, but that eventuality can be delayed for an extremely long time.

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Zamfir
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Re: Stable free oxygen on non-life planet

Postby Zamfir » Mon May 14, 2018 7:49 pm UTC

Is this very different from our world? I am not sure, but was under the impression that all oxygen sinks have been oxygenated for a long time, and the current situation is basically a closed biological cycle of drawing oxygen from carbon and attaching it again. If the production of oxygen stopped, all stored biomass carbon would eventually react to CO2, but there's far more oxygen in the atmosphere than that.

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Eebster the Great
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Re: Stable free oxygen on non-life planet

Postby Eebster the Great » Tue May 15, 2018 10:30 am UTC

It's not just biomass carbon that you have to consider, it's the billions of years of buried and weathered carbon. Prior to the Siderian period of the Paleoproterozoic era, there was no free oxygen in the atmosphere. The early atmosphere was also far denser than the atmosphere today. Oxygen is still weathering into fresh rock that is exposed by crustal movement, which is why I said you would want to avoid that. You would also want to avoid digging up carbon veins and burning them the way we tend to do. But the fact that such veins exist demonstrates the idea that the oxygen isn't really free from its carbon nemesis forever, and it is certainly not the case that "all oxygen sinks have been oxygenated for a long time."

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Himself
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Re: Stable free oxygen on non-life planet

Postby Himself » Fri May 25, 2018 4:28 am UTC

One instance where you might get the stable free oxygen is on a water world with oceans deep enough the bottom would consist of high-pressure ices. That would prevent or at least greatly inhibit any interaction between the atmosphere and rocky crust. Not only would it act as a barrier, but, I've also seen it suggested that the pressure from such a deep ocean would prevent magma formation, which would suggest no volcanism or plate tectonics to renew the crust.
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