August 13, 1998
CORVALLIS, Ore. -- Scientists at Oregon State University have discovered evidence of rock-eating microbes living nearly a mile beneath the ocean floor in conditions which suggest similar life could exist on Mars or other planets. The discovery was announced Friday in the journal Science.
Microbial fossils were found in abundant quantities in miles of core samples taken during various research projects by the Ocean Drilling Program in the Pacific, Atlantic and Indian oceans, according to Martin R. Fisk, an associate professor of oceanography at OSU and lead author on the study.
Where the basalt was glassy, having quickly been cooled by seawater, the scientists found a series of tracks and trails. "Whenever we looked at those tracks for DNA, we found it," Fisk said.
Fisk said he first became curious about the possibility of life after looking at the swirling tracks and trails that were etched into the basalt. The rocks have the basic elements for life including carbon, phosphorous and nitrogen, and needed only water to complete the formula. Groundwater seeping through the ocean floor could easily provide that, he pointed out.
"Under those conditions, microbes could live beneath any rocky planet," Fisk said. "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 by the sun."
Fisk said scientists know a lot about the interior of Mars from meteorites that have been blasted off the planet. "They've got everything you need for life," he said, including carbon, phosphorous, small amounts of nitrogen, and minerals that contain water, or evidence of water.
The temperatures required to create life are less of a concern, he pointed out, as scientists find more and more evidence of life in some of Earth's most desolate and extreme conditions -- from Antarctic ice to deep ocean vents.
Microbes have been found near temperatures reaching 113 degrees C, and in freezing brines some 15 degrees below zero, Fisk pointed out.
"The surface of Mars may be too cold to find life unless there is a hot spring bubbling up," Fisk said. "But every planet has a temperature gradient; they get hotter as you go down. Within the next few years, we'll probably find life on Mars.
"But we may have to dig to find it," he added.
Fisk said the evidence of microbial activity could be bacteria, or archea -- which are the same size, but "as different from bacteria as humans." A third, more distant possibility, the scientists say, is that the tracks and trails are a new, undocumented chemical process.
The glassy, outer inch of the basalt is the only place evidence of microbial activity was found. Fisk thinks the looser chemical structure of the quickly-cooled rock makes it easier for the microbes to break it down than the more tightly-bound inner rock which cooled more slowly.
"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. One theory is that they are seeking micronutrients in the rock -- iron, potassium or sulfur -- which they need in small amounts.
"They may also be dissolving the rock to get a certain chemical reaction to provide them energy."
The researchers believe the microbes were originally carried beneath the ocean floor in seawater, seeping into the basalt and settling in fractures created by cooling. Inside of dying, however, the microbes found the necessary ingredients within the basalt to continue living. The DNA was found in the most far-reaching tubes within the fractures, Fisk said, indicating the microbial activity took place on site, beneath the ocean floor.
The researchers say the next step is to bring up fresh core samples and try to extract the microbes while they are still alive. The core samples were from drilling studies that were months, even years old, and had been stored at Columbia University, Texas A AND M and the Scripps Oceanographic Institute. Future drilling studies are being proposed that would include an effort to extract and preserve living bacteria. The project is funded by the Ocean Drilling Program and the National Science Foundation.
Stephen Giovannoni, an associate professor of microbiology at OSU, says preserving live microbes from rocks found a few feet to nearly a mile beneath the ocean floor will not be easy.
"It is possible, but it will be difficult," Giovannoni said. "Other scientists are working to provide better samples of the subsurface microbial world, and there are efforts under way to develop new 'clean' drilling techniques. The drill itself can be a source of contamination.
"There also are huge pressure differences between the deep sea floor and the ocean surface," he added. "That makes it unlikely that these organisms will be cultured in a lab anytime soon."
Researchers Paul Johnson, of the University of Washington, and Jim Cowen, of the University of Hawaii, are collaborating with the OSU researchers to collect samples from hot springs on the deep sea floor using the Alvin, a deep sea submersible.
The scientists hope their discovery opens the doors to further research of potential living organisms beneath the ocean floor.
"For the moment, the problem remains providing even stronger evidence, including gene sequences, that would conclusively prove there are living organisms down there," Giovannoni said.
National Science Foundation
August 13, 1998
"This is an important step forward in our continuing efforts to understand the processes that sustain life deep beneath the earth's surface," says Mike Purdy, director of NSF's LeXeN program. "Negative findings like this are as important as positive ones in their importance to our understanding of the processes that determine the limits to life."
It had been generally accepted by scientists that hydrogen gas produced from rock could provide energy to support the growth of microorganisms living below Earth's surface, says U. Mass. microbiologist Derek Lovley. The hydrogen was thought to be produced when basalt, a common form of rock, reacts with water.
However, a research team led by Lovley has found that this concept is incorrect. Although hydrogen gas can be produced from basalt under artificial laboratory conditions, there is no hydrogen production under the conditions actually found in Earth's subsurface.
Lovley and his colleagues found that hydrogen could only be produced from the basalt when the rock was exposed to acidic conditions -- but environments containing basalt are never acidic.
"The idea that hydrogen produced from rocks could support large subsurface microbial ecosystems on Earth and possibly other planets was fascinating and was accepted by most microbiologists," Lovley says. "Unfortunately, this concept can not be supported by the available data."
From analyses of chemical and microbiological data, Lovley and collaborators Robert Anderson, U. Mass. graduate student, and Francis Chapelle, a hydrologist at the U.S. Geological Survey in South Carolina, suggest that the microorganisms are probably living on organic matter associated with the rock, not hydrogen. This is similar to the way that microorganisms grow in soil on Earth's surface.
The scientists emphasized that even though the microorganisms living deep in the Earth may make a living in a manner similar to that of surface microorganisms, they may have other unique characteristics. For example, Lovley's recent research has demonstrated that microorganisms from the earth's subsurface can be used to remove radioactive metals, as well as hydrocarbons from polluted groundwater.
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