Biosphere III – bacteria found living 1,7000 feet beneath sea floor – special issue: 1994

Biosphere III – bacteria found living 1,7000 feet beneath sea floor – special issue: 1994 – the Year in Science

Tim Folger

Life on Earth, for all its diversity, exists within relatively narrow borders, from the seafloor to the mountaintops. At least that is what the scientists have always thought. Last September, though, British researchers announced that they’d discovered an entirely new realm of life. Large numbers of bacteria, they said, live at depths of 1,700 feet or more below the seafloor.

Some researchers heave speculated for years that Earth might harbor such a “deep biosphere.” But until now evidence has been scant. Bacteria have turned up at oil-drilling sites, for example, but the possibility that such microorganisms were really surface dwellers that had contaminated the samples could never be ruled out.

The British group has come up with more-solid evidence. THey’ve isolated bacteria from sediment samples drilled at five sites – four in the Pacific and one in the Sea of Japan. Unlike earlier work, there is not much chance that these samples are contaminated. For one thing, the researchers examined the bacteria directly in the sediment cores, without first removing and culturing them – a step that often introduces contaminants. For another, in some parts of the sediment cores the number of bacteria increases with depth, which is difficult to explain by means of contamination.

Although the drilling samples came from a maximum depth of 1,700 feet, the researchers suspect that life extends still deeper. Even at 1,700 feet, bacteria counts were still high – about 170 million per cubic inch of sediment. (By comparison, a typical cubic inch of garden soil might contain 30 billion bacteria.) “It’s quite reasonable to expect bacterial populations to go much deeper than the 1,700 feet we’ve been able to get samples from,” says biologist John Parkes of the University of Bristol, a member of the British team.

How did the bacteria get down there? Parkes thinks it most likely that they were simply buried over time by the steady rain of sediments onto the seafloor and gradually evolved to cope with high pressures and temperatures. Some of them seem to be living off organic carbon in the sediments. But Parkes frankly admits that he and his colleagues know little about how the bacteria survive. All are anaerobic – oxygen poisons them – and genetic analysis indicates that many are at best distantly related to known surface bacteria.

Perhaps most surprising is the sheer size of this new biosphere. If the samples the British team has found are typical of what lies below us, the mass of subterranean bacteria may be equivalent to 10 percent of the total mass of all surface life. “And that’s just to 1,700 feet,” says Parkes. “We suspect they might go much deeper. THere’s a huge amount of extra data to find out. We’ve just had a stimulating peek.”

COPYRIGHT 1995 Discover

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