For several decades now, researchers have furiously debated whether life can exist elsewhere in the solar system. The naysayers argue that without the carbon-hydrogen compounds necessary to most life on Earth, these extraterrestrial beings would have nothing to eat. Now a study of deeply buried rocks in Idaho has demonstrated that hydrogen produced by geochemical forces can be an adequate food source, at least for some unusual microbes.
Francis Chapelle, a geohydrologist from the U.S. Geological Survey in Columbia, South Carolina, and Derek Lovley, a microbiologist at the University of Massachusetts, Amherst, have been searching for places on Earth that lack organic carbon and that thus approximate conditions on, say, Mars or one of Jupiter's moons, Europa. The researchers also suspect any extraterrestrial life would exist underground, because such creatures would still need water and, as far as we know, surface water exists only on Earth. Looking for a likely model of extraterrestrial conditions, they collected water samples from rocks 200 meters below a hot spring.
As the researchers hoped, the water had very little organic carbon and yet was teeming with microbial life, in particular a group of microbes called archaea. Genetic studies showed that these archaea are very closely related to previously discovered surface archaea that feed off hydrogen; they combine hydrogen with carbon dioxide to make methane, the researchers report in the 17 January issue of Nature. On the surface, these methane-generating bugs are rare, but 200 meters down, they are the dominant life-form and could form the basis of an entire community, Chapelle and Lovley report.
"The work is very solid and exciting," notes Tom Kieft, a microbiologist at the New Mexico Institute of Mining and Technology in Socorro. He says it gives a boost to those seeking to show that there could be extraterrestrial life.