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Saturday, February 15, 2003
A world of new life forms thrives below ground, researchers say
Simple life forms are turning up in a surprising variety
of below-ground environments, potentially making up 50
percent of the Earth's biomass, scientists said today
at the American Association for the Advancement of
Science (AAAS) Annual Meeting.
From South African gold mines, to cooled seafloor lavas,
these subsurface bugs have provided clues to the
potential for life on Mars, and the diversity of possible
fuel sources for life, including nuclear energy and
toxic waste.
Similar Environments on Mars
Life on Mars may exist in "pillow lavas," volcanic rocks
that are common on and below the terrestrial seafloor,
according to Martin Fisk of Oregon State University. He
and his colleagues have investigated the bacteria that
live inside pillow lavas on Earth, and found that the
microbes seem to be getting their energy from reactions
between the glass in the rock and water.
Pillow lavas are likely to exist on Mars, Fisk said,
and their unusual bulbous shape should make them easy
to detect as researchers increase the resolution of
photos taken of the planet's surface.
"On Earth, microbes live in the glass of pillow lavas.
Mars could host life in similar volcanic rocks,
although this would require the presence of 'primary
producers' -- organisms that make organic matter from
chemical energy and carbon dioxide," Fisk said. "We're
currently working to identify those microbes in Earth's
volcanic rocks."
Pillow lavas form as seawater rapidly cooled molten
lava into volcanic glass. Because these glasses don't
have internal crystal structures, the way minerals do,
bacteria leave distinctively-shaped tracks as they
bore minute holes into the glass.
"I sometimes joke that if NASA could get me a pillow
lava, I could tell you if anything ever lived in it,"
Fisk said. He noted, however, that the rock would have
to be well-preserved.
Life doesn't have to be from another planet in order
to survive in seemingly inhospitable conditions, other
speakers in the AAAS panel have discovered.
Getting in Deep
Tullis Onstott of Princeton University and his
colleagues have found bacterial populations within the
walls of South African diamond mines, at depths between
0.8 and 3.3 kilometers. There, temperatures reach up
to 60 degrees C and pressures are nearly 250 times as
high as on the surface.
The microbes that Onstott and his colleagues have found
are unlike any living near the Earth's surface. They
may even be deriving their energy from nuclear power,
at least indirectly.
Water plus nuclear radiation emitted from rocks, such
as those in the mines produces hydrogen, oxygen, and
hydrogen peroxide. The researchers have hypothesized
that the bacteria may be using this hydrogen for fuel.
"The deep subsurface may be the only place on Earth
where communities are using nuclear power that is
natural and environmentally safe," Onstott said.
The bacterial species may also be ancient. New age
estimates from water samples taken from the mines
suggest that the water is up to 100 million years old.
"Studying these unusual, primitive microorganisms
helps us appreciate life's ability to take hold in a
remarkable variety of environments. It may even help
us understand how life evolved on Earth or other
planets," Onstott said.
The Versatility of Life
Closer to home, Susan Brantley of Pennsylvania State
University has grown bacteria on different mineral
surfaces in her lab. Her goal is to understand how
the microbes extract elements from their environment
to sustain themselves.
"Early life had to solve all the same problems" that
these bacteria do, Brantley said. She thinks that
some bacteria's body chemistry may incorporate elements,
such as nickel, that were most accessible when life
emerged on Earth.
"Snapshots of the chemistry of the early Earth may be
caught in these organisms," said Brantley.
Research in thermal hot springs also reveals bacteria's
adaptability to all kinds of environments where
photosynthesis cannot take place. Everett Shock of
Arizona State University studies life in hot springs
such as those in Yellowstone National Park.
Shock and his colleagues have identified more than
a hundred possible types of metabolic reactions in
which the organisms derive their energy from chemical
reactions. While these include familiar reactions
involving hydrogen, iron, sulfur, nitrogen, and
organic compounds, they also involve more unusual
elements, such as arsenic, selenium, and uranium.
Other metal-reducing bacteria may have potential for
use in environmental cleanup efforts, according to
John Zachara of the Pacific Northwest National
Laboratory.
Another unsung role played by bacteria involves the
formation of large deposits of methane hydrate on the
seafloor. These deposits are solid under the high
pressures and low temperatures at the seafloor. If
that pressure were reduced or the temperature
increased, however, the hydrate would likely vaporize,
producing large volumes of methane, a potent
greenhouse gas. Scientists have proposed that methane
hydrates may have had a hand in past climate change
episodes, or may be a possible fuel source.
Frederick Colwell of the Idaho National Engineering
and Environmental Laboratory has identified some of
the microbes that make the methane in these deposits.
Colwell and his colleagues are now trying to determine
the rate at which these bugs produce methane, which
should help researchers predict where methane hydrates
are located.
Source: AAAS
