Deep beneath the dry sagebrush along the Columbia River in Washington, scientists have found a bizarre community of bacteria that live only on rock and water -- the first example of the kind of life that might exist on Mars.
The discovery, announced in Friday's issue of the journal Science, also demonstrates what life might have looked like on Earth more than 2.8 billion years ago, before plants evolved and began pumping oxygen into the atmosphere.
"It demonstrates the extremes in which life can survive, and demonstrates that life can truly survive on the kind of materials and conditions that existed long ago," said David Des Marais, a researcher at NASA's Ames Research Center in Mountain View who studies the early Earth.
He added that the discoverers will have to do more work to prove conclusively that these bugs need only rock and water to survive -- getting no outside help in the form of oxygen or other nutrients trickling down from the surface.
Christopher McKay, a NASA/Ames physicist who has been studying the possibility of life on Mars, said he was thrilled when he heard about the study at a meeting last summer. He and two colleagues had proposed in 1992 that life may persist on Mars deep within hot springs -- and that, like these bacteria, it would consume carbon dioxide and hydrogen.
If the results of the study are confirmed, this would be the first community of living things ever found on Earth that don't depend, even indirectly, on photosynthesis to survive.
The bacteria were found on the Hanford Nuclear Reservation. Microbiologist Todd O. Stevens and geochemist James P. McKinley of Pacific Northwest Laboratory have been prospecting there for five years, trying to find microbes that might be useful in cleaning up contaminated aquifers.
Drawing water from wells, they found surprisingly large numbers of microbes living in aquifers as deep as 1,300 yards, in water that had percolated down from the surface thousands of years earlier. Although conventional food was scarce, up to a million microbes teemed in a volume of water roughly the size of a sugar cube.
They concluded that water reacting with the basalt rock was generating hydrogen gas, which the bacteria gobbled as food. The rest of their diet consisted of carbon dioxide dissolved in the water.
The scientists sealed bacteria in bottles that contained only crushed rock and water from the aquifer. They thrived, secreting a slimy gel that coated the rocks and offered a congenial place to live and multiply.
Researchers christened the little bacterial community SLiME, for Subsurface Lithoautotrophic Microbial Ecosystem.
The researchers said they went to great pains to ensure that nothing from the surface contaminated their bacterial samples.