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The Progenitors are an ancient race of almost infinite technological sophisitication, who mysteriously vanished millions of years ago for no good reason (I don't like TV Tropes, but you are welcome to google it).

In their myriad travels around the cosmos, they have taken a shine to creating new worlds. They are, of course, quite biased towards oxygen-having worlds suitable for human life. Photosynthesis works great, but supposing the progenitors wanted to seed a world with life that was dozens of AU from the sun (like Europa), shrouded in a hazy atmosphere (Venus), or both (Titan)?

What metabolic processes could the progenitors engineer into organisms in order to create an oxygen atmosphere and maintain it over time, where the energy source is not sunlight?

Assumptions

  • This planet has an iron core, volcanic and tectonic activity, a rocky crust, and at least some oceans. None or all of these can be used to support your oxygen-making organisms.
  • The focus is on the chemical reaction to produce oxygen, that will replace photosynthesis. Details of the creature itself (carbon based, silicon based, exotic, etc) are not so important.
  • The creatures must stick around long enough to maintain the oxygen atmosphere for billions of years until humans come.
  • 1 atm air pressure and 0.2 atm oxygen partial pressure are not required, but desired.
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They have near infinite technology? Photosynthesis (how we normally generate oxygen) requires energy; it's an endothermic process. With energy, it can occur. So where does the energy come from without sunlight? The energy comes from the world's core.

Your organisms perform chemosynthesis at the (abnormally many) hydrothermal vents. The (abnormally active) vents will give enough light for your microbe to produce oxygen, and will continue to give your organisms energy for millions of years. Interestingly enough, there is an article about obligatory photosynthesizers on Earth that use hydrothermal vents: http://www.pnas.org/content/102/26/9306.full. Nice reading, I recommend it.

Here is a quote:

If photosynthesis could take place in geothermally illuminated environments, it would increase the diversity of photosynthetic habitats both on Earth and on other worlds that have been proposed to possibly harbor life.

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  • $\begingroup$ Geothermally illuminated? $\endgroup$ – RonJohn Sep 13 '18 at 13:53
  • $\begingroup$ @RonJohn That's straight from the article. $\endgroup$ – JavaScriptCoder Sep 13 '18 at 13:54
  • $\begingroup$ @kingledion edited. $\endgroup$ – JavaScriptCoder Sep 13 '18 at 14:01
  • $\begingroup$ I see the quote, but geothermal illumination is -- as far as I understand it -- rock so hot that it glows red and orange. But photosynthesis also needs blue light. $\endgroup$ – RonJohn Sep 13 '18 at 14:09
  • $\begingroup$ @RonJohn as far as I remember, the type of light required is only based on the pigment used in photosynthesis. Plants generally use chlorophyll, but there are also other pigments. I remember asking about this: worldbuilding.stackexchange.com/q/99160 $\endgroup$ – JavaScriptCoder Sep 13 '18 at 14:11

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