4/11/02 7:45:13 AM Pacific Daylight
Time
Source: NASA/Ames Research Center
(http://www.arc.nasa.gov)
Date: Posted 4/11/2002
Hydrogen-Fed Bacteria May Exist Beyond Earth
Primitive bacteria exist in huge numbers deep in
the Earth, living on hydrogen gas produced in rocks, a NASA scientist reports
in the spring issue of the journal Astrobiology. Recent studies suggest that
the mass of bacteria existing below ground may be larger than the mass of
all living things at the Earthâs surface, according to
recent studies cited by the paper's lead author, Friedemann Freund, who works
at NASA Ames Research Center in California's Silicon Valley. Similar
hydrogen-consuming microbes may some day be discovered on Mars, raising new
prospects for the possible existence of life beyond Earth, Freund added.
"The hydrogen that could feed bacteria in the depth of the Earth comes from
a subtle chemical reaction that occurs within rocks that were once hot or
even molten. In the top 20 kilometers (12.4 miles) of Earth's crust," Freund
said, "the conditions are right to produce a nearly inexhaustible supply
of hydrogen. In the top 5 to10 kilometers (about 3 to 6 miles) all fissures
and cracks in the rocks are probably filled with water. Hydrogen molecules
will seep out of the mineral grains, enter the intergranular space and saturate
the water. Microorganisms that live in these water films can be expected
to use this hydrogen as their vital energy source." Many of the microorganisms
in the âdeep biosphere' do not live off the sunlight-derived
energy that green plants trap during photosynthesis, but live on chemically
derived energy sources such as hydrogen, according to Freund. "If deep microbial
communities are to thrive over long periods of time, they need a steady supply
of hydrogen," he said. It has long been known that hydrogen gas is produced
when water reaches freshly formed cracks in many common rocks, but Freund's
paper describes a different hydrogen-producing reaction that occurs inside
the minerals that make up such rocks. This reaction does not require rocks
to crack â a necessarily episodic event. Instead, it occurs
in the entire rock volume during its gradual cooling as continents slowly
age over millions of years. Because the Earth's crust contains a huge quantity
of rock, even a small amount of hydrogen produced in each small section of
rock results in a large volume of gas. To understand the details of this
hydrogen-producing reaction, Freund said, requires some insight into the
structure of minerals where silicon, oxygen and metals have combined to form
a dense pack of atoms and ions. When these minerals crystallize at high
temperatures, water is always present, and some water molecules are trapped
in the atomic structure of the minerals, said Freund. These water molecules
are ripped apart and change into hydroxyl anions, each of which is negatively
charged and has one oxygen ion with a proton attached. "During cooling, at
temperatures below 400 to 500 degrees C (752 to 932 degrees F), a strange
reaction takes place. Pairs of these hydroxyl anions rearrange their electrons
in such a way that hydrogen gas molecules are formed," Freund said. What
is unusual and still not fully understood, said Freund, is that the electrons
needed to make the hydrogen molecules are taken away from negatively charged
oxygen anions. "Suddenly, some oxygen anions, which everybody thought only
existed in a doubly charged negative state, convert to singly charged negative
ions," he said. "These single negative oxygen anions join in pairs. In this
form, they are innocuous and can stay inactive over geological times." The
hydrogen molecules, however, wander around inside the mineral structure and
can squeeze into the narrow spaces between the mineral grains. If the
intergranular space is filled with water, the hydrogen molecules will dissolve
in the water. If microbes live in the intergranular water films, one can
imagine, said Freund, that these bacteria extract the dissolved hydrogen
from the water and use this hydrogen as an energy source, not unlike fish
that extract oxygen dissolved in the water of rivers, lakes and the sea to
respire. "What is potentially important," Freund said, "is that, if and when
microorganisms in the deep underground use this hydrogen dissolved in the
intergranular water films, the rocks around them will replenish the hydrogen
supply - indefinitely, over eons of time." The paper by Freund and his coworkers
also may help answer non-biological questions related to the commercial viability
of tapping hydrogen reserves deep in the rocks and to questions of mine safety.
For example, sometimes, during mining and drilling operations, enough hydrogen
seeps out of wall rocks that explosive gas mixtures can be produced, according
to some reports. "Since old, old times, the mining industry has had its share
of mine explosions in which hydrogen played a role," Freund said, "but hydrogen
gas could also be used as an energy source and fuel in
todayâs or tomorrowâs society. For years,
pipelines have been distributing hydrogen gas between different industrial
partners in the Ruhr Valley in Germany, and the experts say it can be handled
about as safely as natural gas." Editor's Note: The original news
release can be found at
http://amesnews.arc.nasa.gov/releases/2002/02_37AR.html
Note: This story has been adapted from a news release issued
by NASA/Ames Research Center for journalists and other members of the public.
If you wish to quote from any part of this story, please credit NASA/Ames
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http://www.sciencedaily.com/releases/2002/04/020411071455.htm
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