There is evidence that life evolved in the deep sediments. ... There is clear evidence that life existed more than 3.8 billion years ago. Although, for there to be a big enough biomass for us to detect it in the rocks, it must have been evolving long before that. ... The normal view of life on Earth is that the majority of life is on the surface, fuelled by sunlight. And you don't expect a large population - even bacteria - to survive away from that source. But we are finding that there are a lot of geological sources of energy below the surface. For example, there are a lot of processes that produce hydrogen, which is a good source of energy for bacteria. ... It reinforces the idea that this large bacterial biosphere is in fact living rather than fossil bacteria. Some of the cells are imbedded in sediments that are many millions of years old, which means they must be ancient, too. These bacteria are growing very slowly in the subsurface. They could effectively be immortal.
emergence of life immortality bacteria ocean prehistory