If there happened to be extremely radical conditions causing extremely unique evolutionary results, could a carbon-based lifeform hypothetically “drop” oxygen and carbon-dioxide in favor of an entirely different system of respiration? For example: inhaling an ambiguous gas not comparable to any natural gas on Earth, and exhaling helium.

Universe is highly technologically advanced and I’m open to said species being largely to entirely artificial in origin.

  • $\begingroup$ By "drop" do you mean that it originally breathed oxygen and then evolved to another gas? That would be extremely unusual for anything more complex than a bacterium. $\endgroup$
    – Cadence
    Jun 9, 2022 at 1:12
  • $\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$
    – Community Bot
    Jun 9, 2022 at 1:23
  • $\begingroup$ Helium is odd. It doesn't form compounds, but there are clathrates that form under a million or so bar close to absolute zero. Problematic to be able to tell you if there could be life at that temperature - we've not seen it yet anyhow. It's close to the core pressure of Jupiter if that helps. $\endgroup$ Jun 9, 2022 at 1:35
  • $\begingroup$ @Cadence More or less, yes, that’s what I meant. And I can work with extremely unusual. :) This evolution could be artificial, perhaps planned by a larger, experimenting polity if it’s too unlikely to occur naturally. $\endgroup$
    – Octopodes
    Jun 9, 2022 at 1:37

4 Answers 4


We have already examples of carbon based life forms which do not need oxygen: all anaerobic bacteria do it and are killed by the presence of oxygen.

However keep in mind that respiration is a chemical reaction, what one inhales and exhales must be related by a chemical change, for example C, O2 and CO2 or S, H, H2S. Getting helium out in a chemical way is a tad impossible, consider that helium doesn't form any compound, so won't take part in any chemical reaction.

  • $\begingroup$ Okay. Yeah, my species is definitely “advanced”, about as much as a mammal. If getting helium out of a respiration reaction is too unlikely, I can work with changing the exhaled gas to a different compound, but the problem is I’m working with an atmosphere that has to contain both this ambiguous gas and helium. $\endgroup$
    – Octopodes
    Jun 9, 2022 at 1:41
  • 1
    $\begingroup$ An atmosphere can contain Helium (although it's fairly likely to get lost to space with an Earth-gravity planet, our He mostly comes from in-ground resivors reservoirs where it is geologically trapped), but it isn't likely to be taking part in respiration. Even Earth has minute quantities of Neon and Argon as free gasses in the atmosphere. $\endgroup$ Jun 9, 2022 at 3:55
  • $\begingroup$ @SoronelHaetir: Earth's atmosphere has almost 1% argon by volume. That's about 20 times more than carbon dioxide for example. $\endgroup$
    – AlexP
    Jun 9, 2022 at 8:43

Fusion reactor.

fusion schematic


If the key thing here is exhaling helium, a fusion reaction makes helium out of hydrogen. Maybe your ambiguous gas is deuterium. Of course no earthly life has fusion reactions going on inside of them. But you do not specify the scale or time period over which this must take place. Fusion usually involves temperatures and pressures not compatible with carbon based life, but cold fusion is not exactly wild eyed science fiction - a lot of people spent a lot of time looking at cold fusion to see if might work.

An engineered organism that inhaled deuterium gas, exhaled helium and powered itself by fusion would be a fine creature for a fiction.


Nope! Even aerobic organisms on Earth don't necessarily breathe diatomic oxygen, and we don't exclusively produce CO2 as waste products.

We breathe in O2, and excrete CO2, water, and ammonia (which mammals convert to urea). Other organisms could breathe nitrogen oxides, or sulfur oxides, and excrete all of the above plus elemental nitrogen or sulfur.

They could breathe in chlorine or chlorate / chlorite and excrete water, ammonia, carbon tetrachloride, and phosgene.

Or, the oxidation/reduction reaction can be reversed, with organisms inhaling hydrogen and excreting water, ammonia, and methane. Or inhaling carbon monoxide and excreting CO2, ammonia / hydrogen cyanide, and formaldehyde.

The possibilities are... well, not literally endless, but pretty widely varied.


Radioactive Decay

One of the main sources of helium on Earth is the natural decay of heavy radioactive elements, such as uranium. In some places around the world, notably in the damaged reactor at Chernobyl, there exist colonies of radiotrophic fungus which perform radiosynthesis using melanin. Perhaps the creature you are looking for is a radiotrophic organism which takes in ambient radioactivity. It might then store the radioactive material in a shielded organ, and exhale the helium that would be produced by the decay.

Wikipedia: https://en.wikipedia.org/wiki/Radiotrophic_fungus


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