A team led by Stephen Giovannoni of Oregon State University recently sent a submersible to the bottom of the sea off the Oregon coast and extracted water from a borehole 300 feet below the ocean floor. Despite the tremendous pressures and a lack of oxygen or sunlight, the water turned out to be home to a community of microbes thriving deep within Earth's crust. Giovannoni found that the organisms resemble extremophiles, hardy single-celled life-forms that colonize deep-sea hydrothermal vents. Chemical tests showed that the sample is enriched with ammonia, implying that some of the borehole microbes survive by metabolizing nitrogen compounds.
Even more tantalizing is the discovery of organic carbon molecules whose isotopic signature the proportion of atoms having slightly different masses suggests that they originated through a nonbiological process. The ocean floor in this region, called the Juan de Fuca Ridge, consists of magma that rose and cooled where the crust pulled apart about 3.5 million years ago. If its composition is typical, organic molecules may be common throughout Earth's interior. Such compounds could have sustained carbon-based life at great depths, where conditions might have been more stable than on the planet's early surface. "This might be very preliminary evidence that life originated in igneous rock," Giovannoni says.