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Embargoed until 5 P.M., EDT
NSF PR 98-43 - August 13, 1998
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Chemical Reaction Believed to Support Underground
Microbes is Now Unlikely
Findings Could Have Implications
for Life on Mars and Other Planets
A critical chemical reaction previously thought to
support microbial life deep below Earth's surface,
and possibly on Mars, is in fact highly unlikely.
The findings are reported in this week's issue of
the journal Science by researchers funded
by the National Science Foundation (NSF)'s Life in
Extreme Environments (LeXeN) program and affiliated
with the University of Massachusetts at Amherst (U.
Mass.).
"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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