Extremophiles are interesting because they’re eXtreme!
Ars Technica has a summary of recent work looking into one of the extremest of the extreme.
Faced with this evidence, it was fair to wonder just where the outer edges of survival might be. We may have a hint of that from samples taken from deep in South African mines, which show that life can make it nearly three kilometers down, but it’s far from the thriving communities we find in other extreme environments. In fact, it looks like the bacterial “community” in the mine may be comprised of a single species.