The earliest oxygen-breathing bacteria (Evolution)

by dhw, Sunday, October 23, 2011, 17:02 (4588 days ago) @ David Turell

Dhw: We are told that aerobic (= oxygen-dependent) bacteria on land broke down the pyrite, and this released acid into the oceans. Why then do the researchers argue that our ancestors started off in acidic water? Why weren’t the preceding oxygen-dependent land bacteria our ancestors?

DAVID: Not silly. Misunderstood. First were the cyanobacteria which used a metabolism that created some oxygen in the atmosphere, which did not have oxygen at first. Once enough oxygen appeared than organisms could appear that used oxygen. The acidic water is where the researchers found the organism, presently. they think it needed the water and never changed.

Thank you for this explanation, but may I try your patience just a little further? The researchers expressly talk of aerobic bacteria (= organisms that used oxygen) breaking down the pyrite on land, so their oxygen-dependency PRECEDED that of the bacteria in the acidic water. Konhauser, however, says the water-based bacteria constituted the “first primitive oxygen-dependent life form”, and “our ancestors started off in a pool of highly acidic water”. The water didn’t become highly acidic until land-based bacteria that were ALREADY oxygen-dependent had broken down the pyrite, in which case I still don't understand why they weren’t the ancestors that started us off. Apologies if I’m being obtuse, and I promise not to badger you with this again!