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SvenTropics t1_j1a9m7k wrote

Reply to comment by CommunicationFun7973 in Mars' ancient atmosphere may not have had much oxygen after all by pecika

Well, the question is where did it come from? Oxygen is highly reactive, even in space. We also know that mars had a liquid ocean and a magnetic field once upon a time. Earth was like this too with almost no oxygen in the atmosphere for millions of years. During that time, life was evolving. Eventually some microorganism evolved photosynthesis and proliferated rapidly with seemingly limitless energy, abundant CO2 and no competition. This caused a massive swing in a geologically short period of time from nearly no oxygen in the atmosphere to oxygen being very plentiful as it was essentially a waste product of the process.

The high reactivity of Oxygen made it toxic to nearly all life on earth causing a mass extinction of most organisms. The ones that evolved to tolerate it survived.

On Mars, there's no proof that such a process happened, but I think it did. I believe photosynthetic life existed on there for millions of years. After it all died off, the oxygen gradually reacted with the surface and carbon in the air until O2 levels were mostly gone.

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patricksaurus t1_j1akmsm wrote

Oxygen is the most abundant element in Earth’s crust. It’s the third most abundant element in the universe. The null hypothesis of abiotic iron oxides has to be rejected before you speculate about life on Mars based on iron oxide mineralogy.

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EmperorHans t1_j1c5kdv wrote

Man, I had a wildly misinformed idea of what's in earths crust. I just looked up the top ten, and that list looks nothing like I wouldve guessed.

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patricksaurus t1_j1c8u4n wrote

Oh this is an interesting comment for me. Do you mind telling me what you expected? Not strictly as a list, just sorta what you thought and maybe why? I’m always curious about this kind of thing.

For instance, I expected a more hydrogen, just because of its abundance in the universe.

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SvenTropics t1_j1anb94 wrote

"Molecules containing Oxygen". O2 is wildly reactive. It doesn't stick around long.

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Fyrefawx t1_j1av893 wrote

I’ll never get over the fact that oxygen caused an extinction at one point and now nearly everything requires it to survive.

It’s so wild how life was able to change the the planet itself long before humanity arrived.

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SvenTropics t1_j1d0el0 wrote

I mean if life somehow evolved to survive in sulfuric acid, it would grow to require it.

On one hand, oxidation is deadly to organisms. On the other hand, the reactiveness of it is a great resource for generating energy.

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CommunicationFun7973 t1_j1aaesn wrote

Yes, oxygen is highly reactive. Tends to react with iron pretty often in the universe, often being either metal oxides or water. Geological processes can transfer oxygen too without it being in elemental form.

So to answer your question, it came from space, likely reacted in space then came down from asteroids. So this iron was likely like this before Mars came to be. But also the very surface over billions of years WILL come into contact with elemental oxygen in space.

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Lithgow_Panther t1_j1afhxh wrote

Why do you believe that?

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SvenTropics t1_j1an5v9 wrote

It seems like the most intuitive source for all the oxidation on the planet.

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Lithgow_Panther t1_j1as6l4 wrote

Abiogenesis + evolution of photosynthesis is more intuitive than, say, water ionisation and molecular oxygen formation?

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Underhill42 t1_j1f8p4o wrote

On Earth it took something like a billion years after photosynthesis evolved before there was any more than trace amounts of oxygen in the atmosphere - oxidation stripped it out of the atmosphere just as fast as it was produced, until there was nothing left to oxidize.

Meanwhile, as others have said, oxygen is one of the most abundant elements in the universe, and makes up a huge percentage of the mass of all rocky planets (ballpark of 40% based on available samples) , it's very possible that Mars was well and truly oxidized just as soon as the surface cooled down enough for stable oxides to exist. Heck, the proto-planetary cloud that eventually became Mars was almost certainly already incredibly rich with oxides long before the planet formed - but the heat of formation would have driven off the oxygen from all but the most stable oxides until temperatures cooled again.

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