PORTLAND, Ore. -- More evidence that life can exist under the harshest, most extreme conditions deep inside the Earth suggests that expeditions to Mars or Jupiter's moon Europa could find teeming colonies of underground microbes, scientists said.
"But we may have to dig to find it," said Stephen J. Giovannoni, an Oregon State University microbiologist.
In a report published Friday in the journal Science, Oregon State oceanographer Martin Fisk and Giovannoni say they found traces of DNA in tiny channels or tracks cut through basalt taken from the bottoms of the Pacific, Atlantic and Indian oceans.
The volcanic rock samples, collected several feet to nearly a mile below the sea floor, also contained carbon, phosphorous and nitrogen -- "everything you need for life," Fisk said.
The evidence poses the possibility that it "would be no problem to have life inside of Mars, or within a moon of Jupiter, or even on a comet containing ice crystals that gets warmed up when the comet passes the sun," he said.
Other scientists agree there is a growing body of evidence suggesting that microbial life can exist just about any place there is water.
Deborah Kelley, a University of Washington marine geologist who is studying undersea vents, said research has shown that otherwise barren undersea areas are covered with microbial mats after vents erupt, suggesting the microbes live all across the sea floor and blossom when conditions are just right.
"When you have an eruption on the sea floor, you have large amounts of hot water," Kelley said. "It's like ash cloud but it's really plume of hot water. Everything the microorganisms need to grow in the absence of sunlight is in the plume itself."
Fisk and Giovannoni found evidence the limits of microbial life extends even deeper, well into the basalt layers that form the bottom of the oceans.
"The microbes would make these little tubes, and inside them were germ-sized bodies," Fisk said. "They are either eating the rock or excreting some kind of acid that is doing it."
The DNA was found in the most far-reaching tubes within cracks. The OSU researchers have been able to obtain only small fragments of the DNA and have not identified what the microbes are.
They could be bacteria, or one-celled organisms called archaea. Some scientists have suggested that archaea, which live in extreme environments, may represent the Earth's earliest forms of life.