In years past, scientific speculation about how life began on Earth envisioned primordial soups and slimy goo as the incubators in which the first tiny microorganisms developed, billions of years ago. More recently, microbiologists have examined places formerly seen as too harsh and inhospitable to foster biology, seeking answers about how life developed and adapts. Hydrothermal vents, for example 鈥� areas on the ocean floor that expel seawater superheated deep in Earth鈥檚 crust 鈥� and the exotic creatures that live there have received increased attention. Now scientists are scrutinizing another location for clues in unraveling some of life鈥檚 riddles 鈥� deep in the ground, underneath the planet鈥檚 surface. 鈥淲e鈥檝e pretty much left Darwin鈥檚 warm little pond in the dust,鈥� said David Stahl, a 91探花professor of civil and environmental engineering whose work focuses on ecology and evolution. 鈥淭he subsurface is being increasingly viewed as an important and largely unexplored part of the biosphere. Depending on how you calculate it, its biomass may exceed the biomass on the surface of the planet.鈥� Stahl鈥檚 work examining sulfide-eating bacteria from deep in the Earth has revealed genetic similarities in the microorganisms from different parts of the world, hinting that the existence of such life may be widespread throughout the planet鈥檚 subsurface. Those microorganisms, he added, are among the more primitive, in terms of their metabolism, of Earth鈥檚 life forms. He and 91探花colleague James T. Staley, a microbiology professor in the School of Health Sciences, joined Abigail Salyers of the University of Illinois Urbana-Champaign and Edward F. Delong of the Monterey Bay Aquarium Research Institute for a special session on 鈥淭he New Biology of Rocks鈥� at the annual meeting of the American Association for the Advancement of Science in Boston last week. Stahl has spent the past several years gathering samples from wells drilled in eastern Washington for use as deep-injection sites to dispose of hazardous waste. The drillers tapped into an artesian system and couldn鈥檛 use the wells for disposal, so they were capped. Industry鈥檚 loss was science鈥檚 gain 鈥� the wells provide ready access to tiny microorganisms that exist deep within the earth. These deep subsurface habitats are are radically different from 鈥渟urface鈥� biology. They never see the sun, so energy from photosynthesis, which provides the platform upon which life on the Earth鈥檚 surface is built, isn鈥檛 an option. Oxygen and fixed carbon are scarce, so they must 鈥渆at鈥� inorganic compounds 鈥� such as hydrogen, CO2 and sulfate 鈥� that originate from geothermal processes in the Earth鈥檚 hot interior. Stahl and his collaborators compared those bacteria with bacteria they extracted from deep in African gold mines and from geothermal springs in Yellowstone, and found some strong similarities based on comparative sequencing of genes. That provides a yardstick for estimating evolutionary relationships among them. The studies suggest that the organisms are specialized for life in the subsurface and are very widely distributed on Earth. So did life start in the rocks? Stahl will be the first to bluntly say, 鈥淲e don鈥檛 know.鈥� But it鈥檚 a new place to look for answers about biological diversity and how that diversity relates to environments that used to be seen as barren. And who knows what further research will uncover? 鈥淭here are some things that make it an attractive option 鈥� at the time we think life arose, the Earth was undergoing almost constant bombardment by asteroids and the like, which should have been enough to kill anything that developed on the surface, including microorganisms,鈥� he said. 鈥淭his scenario would provide shelter from what was happening on the surface. But the bottom line, at this point, is that we really don鈥檛 know enough to know. We鈥檙e just getting to the point that we can start to ask these questions.鈥�