The research was done off the coast of Oregon near a sea-floor spreading center on the Juan de Fuca Ridge, by scientists from Oregon State University and several other institutions. It will be published Friday in the journal Science.
In 3.5 million-year-old crust almost 1,000 feet beneath the bottom of the ocean, researchers found moderately hot water moving through the heavily-fractured basalt. The water was depleted in sulfate and greatly enriched with ammonium, suggesting biological activity in a high-pressure, undersea location far from the types of carbon or energy sources upon which most life on Earth is based. It was one of the most precise biological samplings ever taken from deep under the ocean floor, scientists say.
"This is one of the best views we've ever had of this difficult-to-reach location in the Earth's crust and the life forms that live in it," said Michael Rappe, a research associate at OSU. "Until now we knew practically nothing about the biology of areas such as this, but we found about the same amount of bacteria in that water as you might find in surrounding seawater in the ocean. It was abundant."
According to Steve Giovannoni, an OSU professor of microbiology and one of the co-authors of the publication, the work represented a highly complicated "plumbing job," among other things. It took advantage of an existing hole and pipe casing that had been drilled previously in that area by the Ocean Drilling Program, through about 825 feet of sedimentary deposits on the ocean floor and another 175 feet of basalt, or hardened lava about 3.5 million years old.
Using the existing casing, scientists were able to fit an experimental seal and deliver to the seafloor, for testing and characterization, the crustal fluids from far below.
"People have wondered for a long time what types of organisms might live within Earth's crust," Giovannoni said. "This has given us one of the best looks we've ever had at that environment."
The researchers found organisms growing without the need to consume organic molecules, as does most life on Earth. Instead, they processed carbon dioxide and inorganic molecules such as sulfide or hydrogen. DNA analysis of these microbes suggested they are closely related to known sulfate and nitrate "reducers" that are common in other environments. The level of biological activity was sufficiently high that ammonia levels in the subsurface samples were 142 times higher than those in nearby seawater.
"As more research such as this is done, we'll probably continue to be surprised at just how far down we can find life within the Earth, and the many different environments under which it's able to exist," Rappe said.
The deep ocean crust, the researchers said, is an immense biosphere in its own right that covers most of the Earth.
By David Stauth, 541-737-0787
SOURCES: Steven Giovannoni, 541-737-1835; Michael Rappe, 541-737-0717