DENVER--Ecosystems kilometers underground seem to thrive on food made via nuclear reactions, according to research presented here 14 February at the meeting of the American Association for the Advancement of Science, which publishes ScienceNOW. At the bottom of a South African mine, microbes apparently use the byproducts of radioactive decay to survive, a completely new way for an ecosystem to work.
Deep underground, uranium atoms in rocks undergo radioactive decay, sending off alpha particles--two protons and two neutrons--that can bump into other molecules and change them. Scientists wondered if that might create gases that microbes could live on. For instance, when particles from uranium bump into water, they can create hydrogen gas, hydrogen peroxide, and oxygen. Microbes might use the hydrogen gas and hydrocarbons formed from the gas as food. Now geomicrobiologist T. C. Onstott of Princeton University in New Jersey has found evidence that underground microbes are doing just that.
To get to one of their study sites, Onstott and his colleagues have to take an elevator 3.5 km down into one of a dozen gold mines in the Witwatersrand basin of South Africa, where they have found microbes living in water trapped in cracks in the hot rock. Hydrogen gas dissolved in the water reacts with carbon gases to form the methane that sustains the microbes in the mine. In principle, the hydrogen could come from the microbes, from water interacting with certain minerals, or from radiolytic reactions. But Onstott found that the hydrogen concentrations were too high to have come from microbes and the necessary minerals aren't in the mines, which leaves radioactivity. Other evidence supports this: When Onstott measured the concentration of helium, which forms from the alpha particles uranium sends off, he found that there was enough radioactive decay to produce the hydrogen gas in the water.
The research demonstrates an exciting new way that microbes may be able to survive underground, says microbial ecologist Rick Colwell of the Idaho National Engineering and Environmental Laboratory in Idaho Falls. "This is an environment that may in some ways be part of a bright spot" for life deep underground--generally not a friendly place for living things, he says.