What I find fascinating is not just that these organisms are living deep underground (where "deep" is measured in kilometers; this is well below dirt levels), but the adaptations that this low-energy environment means as far as timescales. Some of them -- and these are microbes (it's not clear if they're singlecellular or multicellular) -- live for thousands of years, barely moving. One methanogen is described as using the tiny amount of methane it can produce "[not] to reproduce or divide, but to replace or repair broken parts." The rocks move on geological timescales, and so, it appears, does the microscopic life living on them.
Other interesting datapoints are that we're only recently discovering this because of a combination of advances in deep drilling and "improvements in microscopes that allow life to be detected at increasingly minute levels". The depths where the scientists have found life are only limited by the depths of the boreholes, though they've currently not found anything that lives in places hotter than 122C.
Oh, and based on their numbers, they're estimating that this deep-subsurface biomass is about 3-4% of the total biomass on the planet. It's not just a tiny bit of stuff.
There's a bit more at "Science Daily", too.
Crossposted from Dreamwidth (original here), with comments. Comment here or there; comments here will eventually be duplicated to there.