What kind of realistic oxygen producing reaction used by life could exist in a carbon dioxide / ammonia atmosphere? There are also many volcanoes, either immersed or not, water oceans and you can even use silicon oxides or whatever from the crust of my Earth-like planet. The further it is from our actual photosynthesis the better it is, but it still has to be likely.

Note: I know ammonia will react with oxygen as it did on Earth. That is actually the purpose of these organisms.

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    $\begingroup$ I apologize, but the simple word "metabolism" describes an amazingly complex and difficult subject. Creating (or even justifying) an entire metabolism for an ammonia planet is far beyond the scope of this site. click here to see what it took for me to guess at creating a replacement just for glucose. Photosynthesis is a reasonably simple equation, mammilian life isn't by any stretch of the imagination. (*continued*) $\endgroup$ – JBH Aug 16 '18 at 0:21
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    $\begingroup$ A search on this site for ammonia planets comes up with a lengthy list for this popular subject that I suspect you haven't browsed, despite a number of the questions looking like they answer your question. Thus, I'm going to vote to close (VTC) your question as too broad unless you can narrow it down to something more practical than basically inventing an entire biome. $\endgroup$ – JBH Aug 16 '18 at 0:23
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    $\begingroup$ The early atmosphere of our Earth, and the earliest life in the pre-cambrian era that started oxygenation of our atmosphere could offer some examples. @willk 's answer gives the chemistry. $\endgroup$ – pojo-guy Aug 16 '18 at 3:05
  • $\begingroup$ Ammonia and carbon dioxide react together to form the solid amminium carbamate under dry conditions and ammonium carbonate under wet conditions. Both are solids at room temperature, so it is not possible to have an atmosphere composed of ammonia and carbondioxide. $\endgroup$ – Slarty Aug 16 '18 at 9:19
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    $\begingroup$ This is a legitimate biochemistry question. It should not have been closed. It is not an exhaustive list (@RonJohn) the nature of the atmosphere (particularly the free ammonia) greatly limits chemical reactions that could potentially proceed. People who think this is open ended frankly haven't put the research effort in to discover that there is no activation energy in the ammonia + oxygen reaction at reasonably elevated temperatures; thus free oxygen is possibly excluded in an ammonia atmosphere. TLDR: question is legit, there are very few possible answers, reopen. $\endgroup$ – kingledion Aug 16 '18 at 12:29

First: photosynthesis. It is synthesis of sugar which is CHO. You need CO$_2$ and a hydrogen donor; that can be H$_2$O and you get O$_2$ as a waste product or it can be H2S and you get S as a waste product. If you used NH$_3$ for your hydrogen donor(hmmm...) you would get N2 as a waste product. Are you the dude* with the boron planet? You could use boron hydrides and get some sort of boron thing as a byproduct. In all of these - when you are making sugar out of CO$_2$, carbon keeps its oxygens and incorporates them in the sugar.

What about photosynthesis that made a different carbon product? I could imagine an organism that wanted C. Maybe built its body out of C. Allotropes of carbon are super useful - graphene is ultra strong and diamond is ultra hard and conductive and clear and awesome. Even charcoal is durable in the environment for millennia - and in an environment with minimal O$_2$ it would last longer.

Could you have photosynthesis that stripped O$_2$ from C and just kept the C? CO2 + energy -> C and O$_2$.. You could. You would call it photodissociation instead of photosynthesis because you are not synthesizing anything.

Evidence for direct molecular oxygen production in CO$_2$ photodissociation

Abstract Photodissociation of carbon dioxide (CO2) has long been assumed to proceed exclusively to carbon monoxide (CO) and oxygen atom (O) primary products. However, recent theoretical calculations suggested that an exit channel to produce C + O2 should also be energetically accessible. Here we report the direct experimental evidence for the C + O2 channel in CO2 photodissociation near the energetic threshold of the C(3P) + O2(X3Σg–) channel with a yield of 5 ± 2% using vacuum ultraviolet laser pump-probe spectroscopy and velocity-map imaging detection of the C(3PJ) product between 101.5 and 107.2 nanometers. Our results may have implications for nonbiological oxygen production in CO2-heavy atmospheres.

The article is behind a paywall but Google sees the image which shows the intermediate steps to liberating O$_2$ from C with radiant energy.


So that is my answer: catalyzed photodissociation instead of synthesis, producing O$_2$ as per the OP and making carbon allotropes out of the C.

*... and "dude" is now also used as a unisex term

  • $\begingroup$ Molecular oxygen will react with ammonia starting in the 50C range: (many papers, mostly paywalled). I imagine that a recently photo-dissociated oxygen atom would have energy sufficient to react with atmospheric ammonia. Either your planet should be very cold, or your 'plants' need some sort of mechanism to exclude atmospheric ammonia. $\endgroup$ – kingledion Aug 16 '18 at 12:37
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    $\begingroup$ @kingdelion: yes; one cannot have an oxidizing and a reducing atmosphere stably co-existing. Maybe the planet is in flux? $\endgroup$ – Willk Aug 16 '18 at 13:20
  • $\begingroup$ The process you described don't use ammonia so would it be an issue if oxygen reacts with it ? $\endgroup$ – Jean-Abdel Aug 17 '18 at 10:02
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    $\begingroup$ It's very interesting tho, graphite plants instead of cellulose would be cool $\endgroup$ – Jean-Abdel Aug 17 '18 at 10:02
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    $\begingroup$ Yes they could. That is exactly what plants do with sugar! $\endgroup$ – Willk Aug 17 '18 at 22:22

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