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In the answer to this question it is pointed out that while lunar soil may provide nutrients for plants, water and carbon dioxide are also needed. Water seems to be available, but how could there be carbon dioxide, or any carbonaceous material? Is carbon-containing matter known on the Moon?

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  • $\begingroup$ We have two close votes for off-topic. Might be nice to suggest an alternative placement for the q, no? $\endgroup$ – Oscar Lanzi Apr 27 at 7:18
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    $\begingroup$ I voted for "leave open", and I will vote for reopen - I find the close reasons false, if the possible carbon sources of the Moon are not about the Space Exploration, then what the heck would be that "Space Exploration"? The help center defines only general statements, I can't find anything what would make this question offtopic. $\endgroup$ – peterh Apr 27 at 9:30
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    $\begingroup$ Yeah, this is on topic. $\endgroup$ – Ingolifs Apr 27 at 12:23
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I remember reading somewhere ages back that there is enough material in a cubic metre of lunar regolith to make a sandwich. I can't find the original source for that, but this Forbes article makes a similar statement. Keep in mind a sandwich worth of carbon per ~2 tonnes of regolith is still pretty scarce.

Digging around for ppm values, there seem to be between 90 ppm and 130 ppm carbon from the Apollo sources of Lunar Regolith. Link

For the milennials out there, carbon has about half the abundance of diamonds in minecraft.*

As to what form that carbon is in, I couldn't find any information, and suspect it's not really known. I'll quote part of the abstract of this paper.

Although the majority of the solar wind implanted carbon may be released and quantitated by pyrolysis there is little information to identify which elements were bonded to the carbon in the sample, if indeed any bonds were present at all.

The carbon content is analysed by pyrolysis, i.e. heating the sample up a lot and analysing the vapour that comes off. This process breaks the bonds to the other compounds it was originally attached to.

*There is an average of 3.7 diamond blocks per 16384 blocks of stone (1 chunk, or 16 x 16 x 64). This works out to about 220 ppm.

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    $\begingroup$ I don't believe that pure carbon vapour would come off, the necessary temperature is too high, above 3915 K. $\endgroup$ – Uwe Apr 27 at 15:04
  • $\begingroup$ Yes, it would have to combine with something to make a volatile compound. Hydrogen from the solar wind could do that. Possibly oxygen liberated from the rock as well. $\endgroup$ – Oscar Lanzi Apr 27 at 19:08
  • $\begingroup$ I can have a dig around, to try and find out what exactly happens to the carbon during pyrolysis and how it was detected, though I should point out that wasn't part of the original question. $\endgroup$ – Ingolifs Apr 27 at 22:18

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