"Science Daily" http://www.sciencedaily.com/releases/2002/04/020411071455.htm

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 Earth s 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 deep 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 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 today s or tomorrow s 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

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