This is interesting and important but fun fact, maybe not the first case of 2 billion+ yr old microbes. There were microbial organisms found in a mine in Minnesota coming from 2.6 billion year old rock and they suspected they were coming from water trapped when the rock, banded iron formation, formed in an ancient ocean. IIRC there were two bacteria - one that eats sulfur and excretes iron, and one that eats iron and excretes sulfur.
I went there a while back, and I'll second the great tour. It's awesome that they actually maintain the elevator and let people go down. It's a pretty cool experience, though not for the claustrophobic. Never knew about the microbes, that's really interesting!
one that eats sulfur and excretes iron, and one that eats iron and excretes sulfur
Thermodynamically, how could these two cycles sustain metabolism? Were there other processes/species in the mix to introduce chemical compounds that had more energy contained within?
I don't recall as it was mentioned by someone in passing (and stuck with me) but I can tell you that the rocks they were in are exceptionally iron rich, which is why the mine was there.