Living free of photosynthesis.

Microorganisms that could survive on Mars live in the Columbia River's basalt aquifers near Richland, Wash., researchers assert.

For the first time, scientists have found a community of bacteria that requires only carbon dioxide, basalt, and water--substances that lie below the surface of the Red Planet, Todd O. Stevens and James P. McKinley of Pacific Northwest Laboratory in Richland report in the Oct. 20 Science. None of the bacteria relies directly or indirectly on photosynthesis.

"We think these ecosystems in the basalt aquifer are actually the first ones [ever found] that are completely independent [of] photosynthesis," says Stevens. Although some organisms living in hydrothermal vents at midocean ridges and in other, less exotic environments do not depend on plants for energy, they live alongside organisms that do.

"It's fairly convincing evidence that they've put forward," says R. John Parkes of the University of Bristol in England. The several approaches they employed to investigate the organisms "are all in agreement."

The bacteria get the energy they need to fix dissolved carbon dioxide from the hydrogen produced when water interacts with basalt, Stevens and McKinley report. They also produce the carbon that feeds other bacteria, performing the function of green plants, Stevens says. "Only instead of using sunlight, they are using the energy in hydrogen," he explains.

"This may be an example of how life could have existed [on Earth] before photosynthesis"--or nowadays on Mars, he says.

The finding is "very exciting, because it suggests that it's possible that there could be life in the subsurface of Mars, and this is how it could get its energy," says Christopher P. McKay of NASA's Ames Research Center in Mountain View, Calif. NASA hopes to look for signs of bacterial life on Mars.