I’m working on a speculative evolution project where there’s a Europa like moon with a subsurface ocean. This moon recently (about 50 million years ago) came into a habitable range around a k type star. This moon, over millions of years, gained an atmosphere of about 80% oxygen, 12% co2, 3% water vapor, and 5% other gasses with a pressure about .62 atm at sea level. I assume this high oxygen content would make fires much more prevalent, but would it burn any life that came to the surface? Would it stop life from migrating to land due to the chance of bursting into flames at the slightest spark? A 30% oxygen content made a spaceship explode so what could 80% do to life on the surface?
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1$\begingroup$ It didn't explode. It was ravaged by a fire, sparked by an exposed short in an atmosphere saturated with oxygen. $\endgroup$L.Dutch– L.Dutch ♦2025-06-11 04:27:15 +00:00Commented Jun 11, 2025 at 4:27
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2$\begingroup$ The Apollo spacecraft used an atmosphere of 100% oxygen at 0.34 atmospheres, and they went to the Moon and back. The astronauts were fine, except the three who died in the Apollo 1 fire. The morality is avoid any ignition source in an atmosphere of pure oxygen. $\endgroup$AlexP– AlexP2025-06-11 06:17:42 +00:00Commented Jun 11, 2025 at 6:17
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2$\begingroup$ The Apollo 1 was a spacecraft of the Apollo program. They all used atmospheres of 100% oxygen, because that's what they were designed to use. (The idea was to avoid ferrying useless nitrogen all the way to the Moon and back.) (The fire which destroyed Apollo 1 happened during a test when they pressurized the spacecraft with pure oxygen at 1.13 atm, which is my humble opinion is madness.) $\endgroup$AlexP– AlexP2025-06-11 06:22:11 +00:00Commented Jun 11, 2025 at 6:22
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2$\begingroup$ This is unrealistic, isn't it? So much oxygen. In the natural world, fires start due to only a few things like volcanism and lightning. But they would start - converting the oxygen to carbon dioxide or water. Over the span of millions of years your atmosphere would settle down into a balance more suitable for life. You seem to be imposing a condition that's out of balance. Further, oxygen isn't the fuel, it's only the reactant. What's burning? Wood? Too much oxygen kills plants. ... (*Continued*) $\endgroup$JBH– JBH2025-06-11 13:42:02 +00:00Commented Jun 11, 2025 at 13:42
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1$\begingroup$ ... In a nutshell, something's off about the world. However, as-asked the question is too broad and can be answered from far too many perspectives (see the help center's book rule). Who knows what forms of life might evolve on such a world? They may be perfectly capable of withstanding the occasional firestorm, may be naturally incombustible, may actually convert oxygen into something rather than converting carbon dioxide. Can you edit your post to ask a specific, well-focused and reasonably objective question? Otherwise I think it should be closed. $\endgroup$JBH– JBH2025-06-11 13:44:22 +00:00Commented Jun 11, 2025 at 13:44
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2 Answers
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Would it stop life from migrating to land due to the chance of bursting into flames at the slightest spark?
No.
A high oxygen concentration makes fire more dangerous as the materials oxidate faster and thus release the energy faster (e.g. explode instead of just burn).
But as long as there is no fire there is no real danger from high oxygen concentration (as long as the remaining 20% don't consist mainly of highly flamable gasses, which would be very unlikely as a single fire would ignite the entire atmosphere).
The living beings only have to be much more cautious around fires than we have to be on earth.
Smoking is dangerous :-)
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No, Life Adapts to its Environment
Remember, any life evolving on this moon, presumably starting in the oceans, will have been evolving for survival in this environment from the very start. Early amphibious life may only make short jaunts onto land, or in the case of something like a plant, keep most of its biomass underwater or underground. Colonization of land will progress as these life forms adapt to the challenges and opportunities such a high oxygen environment provides. By the time life is living on land full time, it'll be fully adapted to that environment. Fire isn't a deal breaker. Even here on earth, life has adapted to regular fires, and some, like jack pines and lodgepole pines require regular exposure to fire, as their pinecones will not open until exposed to a strong heat source.
High anti-oxidant production is probably a given for all life on this moon, and that will continue out of the seas. Organisms may develop a skin or bark that's full of oxides and suspended water to prevent burning or slow the rate of burning if set on fire. They may go the full mollusc route and cover themselves in slime. Others may take advantage of the high oxygen directly, spraying fuels that are hypergolic with the 80% oxygen atmosphere to make a simple flamethrower. Sessile organisms like plants or barnacles might harden themselves against heat and flame while simultaneously depositing highly flammable waste or debris (like leaves or guano) all around themselves hoping that occasional flash fires will kill off their competitors. It'll be an environment where fire and oxidation are a much more important factor than here on earth, but life will find ways to exploit it.
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$\begingroup$ Exploding, self igniting trees... welcome to sid meir's alfa centauri $\endgroup$Trish– Trish2025-06-17 06:15:13 +00:00Commented Jun 17, 2025 at 6:15
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$\begingroup$ You only need to look off-planet for the self-igniting part. Eucalyptus trees are active pyrophytes. They are fire resistant and produce flammable oils to encourage forest fires, after which their seed pods open. However, if the fires are too hot or last too long, they'll explode. $\endgroup$Shawn O'Neil– Shawn O'Neil2025-06-17 07:16:57 +00:00Commented Jun 17, 2025 at 7:16