Evidence is surfacing that searing temperatures and crushing pressures are creating a storehouse of nutrients needed by microorganisms living at the seafloor and, possibly, deep within the earth's crust.
Microorganisms in the ocean depths thrive where there is no light and dine on chemicals toxic to other life. Deborah Kelley, a University of Washington oceanographer, presents a poster at this week's American Geological Society meeting in San Francisco saying that a significant reservoir of methane and hydrocarbons may be found in rock beneath the seafloor. Such a large food source bolsters speculation about how pervasive these life forms might be.
Kelley has been studying the source of these nutrients in what is called "layer three" of the oceanic crust. Located at a depth of about two and a half miles, this layer consists of rock that was once part of molten magma chambers. Although the basalts found nearly everywhere on the seafloor come from the same submarine chambers, Kelley says that the fluids in layer-three rock are very different from those in basalts because of the environment in which they cooled and evolved.
"In the past everyone commonly assumed that the composition of fluid in basalts on the seafloor is what could be expected deeper in the crust," Kelley says. Starting about 10 years ago, scientists started rethinking this. Kelley's latest work shows that layer-three rock has concentrations of methane that are 50 times greater than that measured in the gases from seafloor volcanoes, the places where lava has been able to reach the surface of the seafloor rather than remaining locked below.
In addition, Kelley and Gretchen Fruh-Green, a colleague from Zurich, Switzerland, have done the first-ever isotopic work on rocks from layer three and the methane does not appear to come from the breakdown of sedimentary material.