What I'm looking at doing is a small game where you land on a planet, and the atmosphere is not survivable by a human being, but there is local life. Over the course of the game, terraforming has to take place, that will allow humans (and other sentient species that just so happen to have exactly identical requirements for breathing as humans) to live in the wildlife of the planet, without completely destroying the local life.

My initial thought was that the flora and fauna be oxygen and carbon based like on Earth, but with a lower concentration of oxygen (maybe 10%?) and then terraform to Earth levels.

Is this viable (Just partially, or in the short term), or would the local wildlife be affected too much by this? I'd like for the the wildlife to just go from outside the terraformed area, into it, without dying, so that they could serve as viable livestock, and for the plants that are viable as crops, to be able to survive as well.

  • It's fine if the animals are actually attracted to the terraformed air, or if the plants somehow grow faster or slower. Anything that presents new challenges is fine, I just want to avoid a dome of death, and for the initial colonists to initially have to use shelters and a oxygen supply mechanic, but later be able to breathe normally.

  • If the oxygen concentration plan isn't viable at all, what are the alternatives?

Notes: For all other intents and purposes, the planet is earth-like enough, that only this one minor thing, whatever that is, prevents full scale colonization. The planets and animals can be eaten, there is water, some of the plant life can be used like wood, but for fuel and for construction, gravity is in the 1g vicinity, pressure at sea level is close to 1 bar, etc...

The terraformed atmosphere is confined inside a energy barrier, that also lessens or magnifies weather effects, but is completely passable by everything else, such that wildlife doesn't even notice the barrier itself.

So the colonization would have to happen like this:

  • Initial shelters, with small engineering team, that rely on oxygen collectors(Or purifiers) to provide clean air.

  • They build a initial terraforming shield, that converts a large enough area that people could exploit the natural resources (including flora and fauna) to support a small town or city, at least in the short term, without having to wear oxygen gear all the time.

  • They expand the initial shield, and then set out to build a few more shields outside of the initial one, to expand the number of potential cities, and create the infrastructure needed to build a machine that converts the remaining atmosphere to one habitable by humans, but without killing of, or otherwise massively destroying the local wildlife.

  • $\begingroup$ From experience we know that if you introduce some kind of "better suited" flora and fauna it will supersede weaker ones. You want to burn the local enviroment with higher oxygen concentration while introducing items that are already adapted to that. Anecdotal example - a plant can adapt from being watered 3 times a week to 2 times a week while watering it 4 times a week would overwater and kill it. $\endgroup$ Commented Jan 10, 2020 at 10:32
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    $\begingroup$ Depending on how exactly the local plants implement photosynthesis, increasing the partial pressure of oxygen may have severe deleterious effects. Depending on how exactly the local plants implement photosynthesis, decreasing the partial pressure of carbon dioxide may have severe deleterious effects. (And the concentration of oxygen is meaningless; what counts it the partial pressure.) (And I don't fully understand what you mean by a "shield". Gases will always mix unless completely isolated.) $\endgroup$
    – AlexP
    Commented Jan 10, 2020 at 10:42
  • $\begingroup$ @SZCZERZOKŁY Ideally, the local plant life would be used, instead of introducing new ones $\endgroup$ Commented Jan 10, 2020 at 10:55
  • $\begingroup$ @AlexP The shield is just a plot device that would allow terraforming of the atmosphere, within a space, without confining movement of wildlife. It's a completely fictional device, and just used as means to achieve story goals, and for the most part, not relevant to the potential answers. I think. $\endgroup$ Commented Jan 10, 2020 at 10:58

1 Answer 1


First of all, you need to distinguish between autotrophs and heterotrophs.

Autotrophs do not need oxygen to thrive, they actually dump oxygen as a waste, and our current atmosphere is the result of the "pollution" photosynthetic organisms have caused in billion years of oxygen dumping.

Heterotrophs need an oxidizer to be able to survive, and if that oxidizer is not oxygen then they will be poisoned by it. If instead they use oxygen, and its concentration is within the limits their organism can tolerate, they will survive, else they will die too. This applies to autotrophs, too.

As you probably know, oxygen is toxic in high concentrations also for humans, that is to say about what I stated above.

Your suggested 10% oxygen is the concentration of oxygen we find on top of the Kilimanjaro or Mont Blanc, quite low but not yet unbreathable for humans. About 6% is what we have on top of Everest, in the so called "death zone".

You might better opt for some gas which is present in the atmosphere and is dangerous for the humans but not for the local species since they are adapted to it. $H_2S$, for example. You would just need to filter it out.

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    $\begingroup$ The flammable and corrosive properties of H2S has the additional benefits of providing further challenges, and justifications for why gear would wear down quicker, so this is a pretty good solution. $\endgroup$ Commented Jan 13, 2020 at 9:37

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