We have yet to drill a hole so deep that we don’t find a microbial population at the bottom of it.
That’s Maciej Cegłowski on Mars for the Rest of Us. Those microbes several kilometers under ground are alive, but in a strange way:
These microbes at these great depths are demonstrably alive, but is this living? In her wonderful book on the topic, microbiologist Karen Lloyd coins the term aeonophile to describe microbiota that live on timescales closer to the geological than the diurnal. Microbes in 101 million year old sediment have been discovered in a dormant but living state, repairing the inevitable radiological damage to their DNA and metabolizing just enough to fight off the depredations of entropy. When a food source appears, their day-to-day speeds up again, sometimes even to the point of reproduction.
Nehaveigur 