[Promalada]

Well, the conclusion of an-aerobic life is actually the obvious one, even if not the only possible maybe. On earth at least, if you detect methan emmitting from a pile of something, the conclusion would be, that something organic inside is rotting (the term might not be correct - ANaerobic rotting, i mean).

I once did an internship at a place, where trash is pre-treated prior to dumping. In that place, the organic components are supposed to be ´eaten´ and burned by aerobic bacteria. I did, for the most part, the measuring, if the process indeed was aerobic. If it wasnt, methane would be emitted, because anaerobic bacteria took over and they ´fart´ (breathe out CH4). Since CH4 is a very potent green house gas, this is not desired. Anyways, point is: If the garbage did emit CH4, we knew it was anaerobic bacteria causing it.

Of course, there are other possible sources for methane, i guess, like vulcanic activity. The biogenic source would need liquid water, too, since the H for the CH4 need to be taken from somewhere by the bacteria.