I was curious if some biological creature, natural or engineered, alien or Earth-born, might technically be able to get oxygen from oxide rocks. I was similar curious if you could atomically break down water, by any biological means, so as to get oxygen and hydrogen from it.

Lunar soil apparently has 45% of its weight in oxygen, for example, and I think oxygen wt% in water is 88%? And according to google, this article claims that, "In most rocks oxygen makes up about 92 per cent by volume; all cations taken together (silicon and metals) make up but 8 per cent by volume."

This made me wonder if you could have an ecosystem where some organism breaks down rocks/soil or water to get oxygen.

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    $\begingroup$ The problem is that both of these would require a lot of energy per the amount of oxygen produced. $\endgroup$ Feb 10, 2022 at 15:14
  • $\begingroup$ Fish perhaps? Their gills collect free O2 from water. Worms absorb O2 through the slime on their skin. A creature that has a similar acidic slime could potentially gather the needed O2 in that manner. $\endgroup$ Feb 10, 2022 at 20:01
  • $\begingroup$ Yes, of course. If you were building that world, what would make any of those ideas invalid? $\endgroup$ Feb 11, 2022 at 0:19
  • $\begingroup$ Breaking down water for the O2 implies they will probably fart H2. $\endgroup$ Feb 12, 2022 at 16:27
  • $\begingroup$ Isn't this (CO2 → O2) what plants are doing? $\endgroup$ Feb 13, 2022 at 0:46

5 Answers 5


The short answer will virtually always be "not without some other source of external energy. In which case you don't need the oxygen either."

That said there's one kind of scenario it could make sense, which I'll come back to after the main stuff.

When chemicals and elements react, to form compounds, the bonds that are formed or broken will mean the reaction needs energy added to happen, or freed energy will be given off. (Technically, there's a bit of wriggle room in that statement, but only a tiny amount, not enough to support a macroscopic body.)

Left to themselves, compounds and elements will tend to form the most stable substances they can, chemically speaking. Because the more reactive, the easier to break their existing bonds, the easier it is to break apart and react into something else. Again, that's roughly correct, not technically perfectly precise.

As an example, elemental oxygen atoms are incredibly reactive, so you tend never to find them wandering round alone - they've reacted with whatever else was present to make iron oxide (rust banded rocks over time) with iron, oxygen molecules with other oxygen atoms, water with hydrogen atoms, and so on. Then within water some will split again, from H2O to ionic forms in equilibrium (H+ and OH-) If we add energy, we can split these apart again - iron oxide back to iron and oxygen atoms, water back to hydrogen and oxygen atoms, etc.

So along comes your organism. To liberate the oxygen again from these, will always require a net input of energy. And because energy is always dissipated in such processes, the usable energy it gets via resulting oxygen just won't be worth the energy it had to get already, to put into the reaction, to free the oxygen in the first place.

Note that none of this is technically precise, and some may have loopholes. You may want to check on Chemistry Stack Exchange if you need to be more sure. You might also find Wikipedia's articles on oxygen in geology, and the great oxygenation event/catastrophe, informative. But that's the rough outline answer.

The one big loophole is this:

Suppose a lifeforms has access to plenty of energy (eg, sunlight) but needs oxygen (or other elements/compounds only found in chemical combinations) for some biological process. Then it might use the external source of energy, and use it to get oxygen and break it down internally from its available form into a more useful biological compound.

But in this case, it would be using the sunlight as its primary energy source, and part of the energy would be "converted" internally so to speak into oxygen for more direct internal purposes, by being used to break oxygen away from whatever it's natively combined with, before using it.

It wouldn't get nearly as much energy from the oxygen as the sunlight it started with, but maybe that's okay. Perhaps it has more than enough primary sources of energy, but biologically ended up developing rocks as an oxygen source for biological processes that are favoured in some way. That's probably feasible. (Carbon life kept underground but with a temperature resilient silicon-based "wings/tail" extruded in daytime, living on the immense raw energy from its blue/UV hot star, but on a desert planet without any significant sources of biologically relevant chemicals apart from underground rocks and deposits???)

That would be a bit like how we get our primary energy from food and oxygen and such, but we don't directly power ourselves from those. Instead we use those things internally to break apart complex molecules and create or store glucose and ATP, which we then use more directly in our bodies to power actual muscles, even though it loses much of the original energy we obtained, in the process of doing so.

  • $\begingroup$ This is a really great answer. Thank you, Stilez. Wish I could select more than one. $\endgroup$
    – Askelad
    Feb 10, 2022 at 12:31
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    $\begingroup$ Updated -added comment at end (last 5 paragraphs and link to relevant Wikipedia article for this if interested) $\endgroup$
    – Stilez
    Feb 10, 2022 at 13:26
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    $\begingroup$ Interesting points. Yeah, I was thinking the creature wouldn't necessarily be powered by the oxygen, I was just wondering about a process it could use to break down the rocks and release it. But it does seem likely it'd want some oxygen for chemical processes, as you say, just as we can't live off glucose alone. I wonder if any of the lithotropes do anything similar to this? $\endgroup$
    – Askelad
    Feb 10, 2022 at 17:56
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    $\begingroup$ I can see another use for oxygen--your solar-powered critter splits water by day and recombines it by night. $\endgroup$ Feb 11, 2022 at 5:11
  • $\begingroup$ For the second part: That is exactly where our oxygen comes from: Plants are taking CO2 and splitting it. Its just our luck that they only care about the Carbon and release the oxygen. But there is no biological necessity in other organisms to not keep the oxygen around $\endgroup$
    – Hobbamok
    Feb 11, 2022 at 13:12


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You may have heard of it. Certainly you are fond of immoderately huffing the oxygen product of photosynthesis. And you, and you. You especially, Zeiss. That oxygen comes from water.

The plants keep the hydrogen from the water to make sugar. Then you eat that.

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    $\begingroup$ That simple sugar has the same count of hydrogen and oxygen atoms as the water that went into it. Canonically, the excess oxygen comes from breaking down the CO2. But even your way, that's what I said -- "plants get away with" this "because they can capture energy from sunlight." $\endgroup$
    – Zeiss Ikon
    Feb 9, 2022 at 18:49
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    $\begingroup$ @ZeissIkon /Canonically, the excess oxygen comes from breaking down the CO2./ howplantswork.com/2009/02/16/plants-dont-convert-co2-into-o2 $\endgroup$
    – Willk
    Feb 9, 2022 at 18:52
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    $\begingroup$ @ZeissIkon Some of the oxygen originally comes from CO2, but all of it passes through water. Plants split water to get hydrogen with which to chemically attack CO2; the oxygen is released, and the hydrogen is used to strip oxygen off the CO2, producing more water. They don't directly split oxygen from CO2. (Of course, it's actually a lot more complicated than that, with CO2 being bound into rubisco and the converted to phosphoglyceric acid rather than being transformed directly into water and formaldehyde, but that's the high-level overview.) $\endgroup$ Feb 9, 2022 at 19:00
  • $\begingroup$ The "photo" in photosyntesis is breaking down the water. The oxygen is released at this stage. The subsequent chemical processes, related to capturing CO2 and making sugars, are called "dark phase" or something similar (it doesn't need light). It is invented somewhat later in the evolution. On the other hand, water and CO2 can swap oxygen atoms by forming H2CO3 so the whole discussion about where the oxygen comes from is pointless, except for understanding the internals of the process. $\endgroup$
    – fraxinus
    Feb 10, 2022 at 7:41
  • $\begingroup$ Hum, now I wonder if there is any bacteria or something that does photosynthesis by something else than typical H2O and CO2. In my brief glance at wikipedia it seems there are many strategies to dealing with either of the two, but both seem to be always present at some point. $\endgroup$ Feb 11, 2022 at 11:58

No, you cant use rocks for oxygen for oxidizing organics, like we do, and get energy.

However, there is a large set of reaction that can substitute the process that you are interested in.

In particular sulphur is common in a form of 'rocks' and it can be used as a weaker way to oxidize stuff. So that it is possible to hunt prey, and then instead of breathing while digesting it, eat some sulphur containing rocks in order to digest the prey.

Problem is that it is likely to be much slower and energy budget will also be somewhat smaller. We cant store oxygen inside of us well, but with sulphur it is easier. So this creature will be able to 'hold breath' for many days, if it has eaten its prey and enough of sulphur rocks. Still, it will be slower overall than us, breathing creatures, because we dont have to carry our oxidizer with us that makes about half of the fuel weight, and oxygen gives about twice as much energy after oxidation is complete. So in starvation mode we can survive about 4 times as long, given the same metabolic rate.

Another interesting concept is that this creature will actually be able to have more stamina on a time frame longer than 10 seconds, but less than 10 minutes. This is when we are limited by our ability to breath. This is a good time frame for hunting. Not ambush-like, peak power for this will be about the same, as ambush hunting doesnt require breathing much. But full pursue and running type of hunting. Lack of muscles for breathing, lack of lungs in general, lack of need for massive resource transfer, can somewhat make up for lower energy output per reaction and double the mass of energy source.

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    $\begingroup$ This was a great answer. Hard to pick between this one and UVphoton's. Hmmm... well, I did like the sulphur eater, and yours is a bit longer, and you're new and could use the points, so I've decided to pick yours. Thanks Seagull, really appreciate your answer! $\endgroup$
    – Askelad
    Feb 9, 2022 at 21:21

There are lithotrophs organisms that "eat" inorganic substrates, as well as chemotrophs. They can get an electron from Iron going from Fe2+ to Fe3+ or sulfur, or other inorganics. Some can do it with just the element, and in others there needs to be a water molecule involved. Some are aerobic processes with oxygen needed as part of the respiration, but others are anaerobic without oxygen.

The moon is also a harsh environment, so you can also have reactions that can be catalyzed by the ultraviolet and in some cases visible light. That could lead to a series of different reactions where if you had a water molecule it could be split. There are people trying to engineer these types of systems to split Co2, or Convert Co2 plus water to Methane etc. So with that extra energy you might be able to shift the balance so oxygen could be obtained by the rock.

You could also think about releasing oxygen from metal oxide compounds by heating them up to release the oxygen. Then if there was free oxygen around it would reoxidize.

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    $\begingroup$ I was gonna make an answer on lithotrophs, but I think you've covered the key points. The one bit you've missed, I think, is that the things that chemotrophs consume are soluble, whereas most of the oxygen-bearing compounds on the lunar surface are either insoluble or very poorly soluble silicates. This makes it exceptionally hard for biological things to actually eat the damn stuff. I don't think silicates are ever reduced on Earth... some small amount of dissolved silica is used for structural purposes in plants and diatoms, but that's all. $\endgroup$ Feb 9, 2022 at 21:15
  • $\begingroup$ This was a great answer, UV. Thank you very much. I didn't end up choosing it as the best/accepted answer, because Seagull also wrote a great answer, and it was really hard to decide which to pick. $\endgroup$
    – Askelad
    Feb 9, 2022 at 21:22
  • $\begingroup$ Stuff that lives on the bottom of the ocean, Chemotrophs +1. heat it up as if they're in close proximity to a 'smoker', +2. And @StarfishPrime - soluble : w/o water there can't be life, +1. $\endgroup$
    – Mazura
    Feb 12, 2022 at 9:35

Lichens can probably liberate some tiny amounts of oxygen since they use acids and enzymes to decompose minerals. They, of course make their own oxygen by photosynthesis. You are probably imagining something with a much greater metabolic rate, but lichens are closer than most life forms we know of that could exist in extreme environments.

  • $\begingroup$ This is a very good point and very knowledgeable. Thank you for sharing! $\endgroup$
    – Askelad
    Feb 10, 2022 at 12:23
  • $\begingroup$ This answer makes an important observation but doesn't finish the thought, how is a mineral going to get to an organism but by being in direct contact or in a solution? Plants can process water and air because they flow naturally, they are fluid, the plants don't have to go get the raw materials because it comes to them. Rock, unless really hot, is solid and so to get taken up into the plant to liberate any oxygen it has to be in direct contact or dissolved in an acid. Get rocks hot enough to flow and biological processes as we know them stop, the rock is sterilized. $\endgroup$
    – MacGuffin
    Feb 13, 2022 at 1:24
  • $\begingroup$ You are correct, yet we know there is water ice on the moon and Mars. Lichens surviving on the moon is a real long shot, not so long as it would be for Mars. They may be the most likely multicellular candidate we know of. $\endgroup$
    – thebanks
    Feb 14, 2022 at 19:41

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