Washington, DC (8/13/98)- The existence of rock-eating
microbes one mile beneath the ocean floor may enhance the search for life
on other planets.
Oceanographers participating in the Ocean Drilling Program now report
the presence of abundant microbial fossils in basalt rock one mile beneath
the Pacific, Atlantic and Indian ocean floors.
Where the basalt was glassy, having quickly been cooled by sea water,
the scientists found a series of tracks and trails. "Whenever we looked
at those tracks for DNA, we found it," Martin R. Fisk, an associate professor
of oceanography at Oregon State University.
The rocks themselves have the basic elements for life including carbon,
phosphorous and nitrogen, and require only water to complete the formula.
Groundwater seeping through the ocean floor could easily provide that,
he notes.
"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."
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.
Martian meteorites that have landed on Earth have revealed a lot about
the interior of the red planet. Studies of these meteorites reveal the
presence of carbon, phosphorous, small amounts of nitrogen, and minerals
that contain water, or evidence of water, "everything you need for life,"
he said.
While Mars was once considered far too cold to support any form of life,
new evidence of life forms surviving in extreme conditions on our own planet,
from the steam in geysers to the ice in Antarctica, have changed this attitude.
Microbes have been found near temperatures reaching 113 degrees C, and
in freezing brines some 15 degrees below zero, leading researchers to believe
Mars could support life.
"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."
Hydrogen Controversy
Meanwhile, related research performed by researchers at the University
of Massachusetts at Amherst questions a leading hypothesis on how these
extremeophiles survive. While it had been generally accepted that hydrogen
gas produced when basalt reacts with water could provide energy to support
the growth of microorganisms living below Earth's surface, the researchers
report that there is no such hydrogen production under the conditions
found in Earth's subsurface.
The researchers 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. Unfortunately, this concept can
not be supported by the available data." says U. Mass. microbiologist Derek
Lovley.
Rather a new analyses of chemical and microbiological data suggest that
the extreme 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.
"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 the National Science Foundation's Life in
Extreme Environments (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."
The research appears in the August 14, 1998 issue of Science.
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