The bacteria are isolated from any surface nutrients.
If life can make it here, it can make it most anywhere.
At least, that's what scientists are saying about a colony of bacteria they found thriving in fractured rock two miles below Earth's surface off a shaft of a South African gold mine.
The bacteria appear to exist completely independently of any support from the surface, relying on the radioactive decay of uranium and other elements in the rock to convert water molecules to usable energy. And they've apparently been living this way for millions of years.
"These bacteria are truly unique, in the purest sense of the word," said Li-Hung Lin, lead author of a report on the single-celled creatures published Friday in the journal Science.
"We know how isolated the bacteria have been because our analyses show that the water they live in is very old and hasn't been diluted by surface water," said Lin. He carried out the research while a doctoral student at Princeton University and as a fellow in astrobiology at the Carnegie Institution in Washington. He is now at National Taiwan University.
The discovery of such a self-sustaining community disconnected from the energy of the sun bolsters the odds that similar life might exist in deep subsurface environments on other planets, such as in groundwater beneath the permafrost of Mars or under frozen oceans on Jupiter's moon, Europa.
"We know surprisingly little about the origin, evolution and limits for life on Earth," said Lisa Pratt, a biogeochemist at Indiana University in Bloomington who took part in the project. "
Scientists are just beginning to study the diverse organisms living in the deepest parts of the ocean.