BLOOMINGTON, Ind. -- Researchers from Indiana University Bloomington and eight collaborating institutions report in this week's Science a self-sustaining community of bacteria that live in rocks 2.8 kilometers below Earth's surface. Think that's weird? The bacteria rely on radioactive uranium to convert water molecules to useable energy.
The discovery is a confirmed expansion of Earth's biosphere, the three-dimensional shell that encompasses all planetary life.
The research has less Earthly implications, however. It will likely fuel optimism that life exists in other deep subsurface environments, such as in groundwater beneath the permafrost on Mars.
"We know surprisingly little about the origin, evolution and limits for life on Earth," said IUB biogeochemist Lisa Pratt, who led IU Bloomington's contribution to the project. "Scientists are just beginning to study the diverse organisms living in the deepest parts of the ocean. The rocky crust on Earth is virtually unexplored at depths more than half a kilometer below the surface. The organisms we describe in this paper live in a completely different world than the one we know at the surface."
Bacteria living in groundwater or in other subsurface environments is not news. Until now, however, it was not known whether subterranean microorganisms were recent arrivals bound for extinction or whether they were permanent fixtures of an unlikely habitat. Also, many scientists have been skeptical of subsurface bacterial communities being completely disconnected from surface ecologies fed by the sun's light.
Pratt, Princeton University geomicrobiologist Tullis Onstatt and former graduate student Li-Hung Lin (the paper's lead author, now at National Taiwan University) and colleagues present evidence the bacterial communities are indeed permanent -- apparently millions of years old -- and depend not on sunlight but on radiation from uranium ores for their existence.