Planets With Oxygen Don’t Necessarily Have Life

[Noclevername]

I thought you were asking another question, and was trying to help with that. I realized that the the original question was about oxygen, which is why I put in the disclaimer, but I thought you wanted to know how toxins could be eliminated without life. The original question was about whether the presence of oxygen indicates life, and I’m not certain how toxins relate to that question.

I did want to know that, and thank you for answering. Maybe I should have started another thread for it.

But in the context of this thread, you said free O2 is a biological product, when the OP says it's clearly not.

[eburacum45]

The worst toxin in this context is probably carbon dioxide. In an atmosphere with lots of abiogenic oxygen, carbon monoxide would be oxidised to carbon dioxide, methane to carbon dioxide and water, ammonia reacts to produce nitrogen and water. So the main danger is a buildup of carbon dioxide. Venus and Mars are examples of planets with atmospheres where carbon dioxide is dominant, and any free oxygen has been absorbed into the rocks.

Abiogenic oxygen is present on Europa and other icy moons, but that's mostly because the rocks are buried deep under layers of ice and water. Io has lost nearly all of its hydrogen and carbon, and the atmosphere is mostly sulphur dioxide, with traces of free oxygen; the presence of free oxygen in this atmosphere doesn't make it breathable, and even if this world's atmosphere was a lot thicker it would still kill you in seconds.

[Jens]

I did want to know that, and thank you for answering. Maybe I should have started another thread for it.

But in the context of this thread, you said free O2 is a biological product, when the OP says it's clearly not.

Yeah, what I meant to say was that I was answering that in the context of the earth, and so it might not really apply to the larger discussion of oxygen and life. I think it's probably better if we focus on that (interesting) question here, about how O2 can emerge without life, and then perhaps that other question, about how toxins are eliminated from the atmosphere could be a different thread.

[Noclevername]

Yeah, what I meant to say was that I was answering that in the context of the earth, and so it might not really apply to the larger discussion of oxygen and life. I think it's probably better if we focus on that (interesting) question here, about how O2 can emerge without life, and then perhaps that other question, about how toxins are eliminated from the atmosphere could be a different thread.

It's OK. I think my question was answered, anyway. I'll withdraw to avoid further derails.

[chornedsnorkack]

Reaction of carbon dioxide with rocks is promoted by liquid water. If Mars were warm and wet, the activity of northern ocean, lakes in Hellas and elsewhere and running rivers would drive down carbon dioxide content of atmosphere.

What is the heavy water concentration on Mars?

[eburacum45]

There isn't much information about the deuterium fraction on Mars, but as one might expect, it seems to be high.
https://science.sciencemag.org/content/265/5168/86

Ion microprobe studies of hydrous amphibole, biotite, and apatite in shergottite-nakhlite-chassignite (SNC) meteorites, probable igneous rocks from Mars, indicate high deuterium/hydrogen (D/H) ratios relative to terrestrial values.

That suggests that there was more water present on Mars in the past, but it has been mostly lost, with slightly more deuterium left behind because it is heavier.