Bacteria under Greenland ice may preview what scientists find underMars' surface (Forwarded)

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University of California-Berkeley

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14 December 2005

Bacteria under Greenland ice may preview what scientists find under Mars'
surface

By Robert Sanders

BERKELEY -- A University of California, Berkeley, study of
methane-producing bacteria frozen at the bottom of Greenland's two-mile
thick ice sheet could help guide scientists searching for similar
bacterial life on Mars.

Methane is a greenhouse gas present in the atmospheres of both Earth and
Mars. If a class of ancient microbes called Archaea are the source of
Mars' methane, as some scientists have proposed, then unmanned probes to
the Martian surface should look for them at depths where the temperature
is about 10 degrees Celsius (18 degrees Fahrenheit) warmer than that found
at the base of the Greenland ice sheet, according to UC Berkeley lead
researcher P. Buford Price, a professor of physics.

This would be several hundred meters -- some 1,000 feet -- underground,
where the temperature is slightly warmer than freezing and such microbes
should average about one every cubic centimeter, or about 16 per cubic
inch.

While Price is not expecting any time soon a mission to Mars to drill
several hundred meters beneath the surface, methanogens
(methane-generating Archaea) could just as easily be detected around
meteor craters where rock has been thrown up from deep underground.

"Detecting this concentration of microbes is within the ability of
state-of-the-art instruments, if they could be flown to Mars and if the
lander could drop down at a place where Mars orbiters have found the
methane concentration highest," Price said. "There are oodles of craters
on Mars from meteorites and small asteroids colliding with Mars and
churning up material from a suitable depth, so if you looked around the
rim of a crater and scooped up some dirt, you might find them if you land
where the methane oozing out of the interior is highest."

Price and his colleagues published their findings last week in the Early
Online edition of the journal Proceedings of the National Academy of
Sciences, and presented their results at last week's meeting of the
American Geophysical Union in San Francisco.

Variations in methane concentration in ice cores, such as the
3,053-meter-long (10,016-foot-long) core obtained by the Greenland Ice
Sheet Project 2, have been used to gauge past climate. In that core,
however, some segments within about 100 meters, or 300 feet, of the bottom
registered levels of methane as much as 10 times higher than would be
expected from trends over the past 110,000 years.

Price and his colleagues showed in their paper that these anomalous peaks
can be explained by the presence in the ice of methanogens. Methanogens
are common on Earth in places devoid of oxygen, such as in the rumens of
cows, and could easily have been scraped up by ice flowing over the swampy
subglacial soil and incorporated into some of the bottom layers of ice.

Price and his colleagues found these methanogens in the same foot-thick
segments of the core where the excess methane was measured in otherwise
clear ice at depths 17, 35 and 100 meters (56, 115 and 328 feet) above
bedrock. They calculated that the measured amount of Archaea, frozen and
barely active, could have produced the observed amount of excess methane
in the ice.

"We found methanogens at precisely those depths where excess methane had
been found, and nowhere else," Price said. "I think everyone would agree
that this is a smoking gun."

Biologists at Pennsylvania State University had earlier analyzed ice
several meters above bedrock that was dark gray in appearance because of
its high silt content, and identified dozens of types of both aerobic
(oxygen-loving) and anaerobic (oxygen-phobic) microbes. They estimated
that 80 percent of the microbes were still alive.

Though methane has been detected in Mars' atmosphere, ultraviolet light
from the sun would have broken down the amount observed in about 300 years
if some process was not replenishing the methane, Price noted. While
interaction of carbon-bearing fluid with basaltic rock might be
responsible, methanogens might instead take in subsurface hydrogen and
carbon dioxide to make the methane, he said.

If methanogens are responsible, Price calculated that they would occur in
a concentration of about one microbe per cubic centimeter at a depth of
several hundred meters, where the temperature -- about zero degrees
Celsius (32 degrees Fahrenheit) or a bit warmer -- would allow just enough
metabolism for them to keep alive, just as the microbes in the Greenland
ice sheet are doing.

Most of the laboratory work was performed by UC Berkeley undergraduate H.
C. Tung of the Department of Environmental Science, Policy and Management.
She is now a graduate student at UC Santa Cruz. Also coauthoring the paper
was Nathan E. Bramall, a graduate student in the Department of Physics.

The work was supported by the National Science Foundation Office of Polar
Programs.

IMAGE CAPTIONS:

[Image 1:
http://www.berkeley.edu/news/media/r...thane_core.jpg
(22KB)]
This series of eight one-meter sections of the lowest part of the GISP2
core gets darker with depth, due to increasing numbers of silt grains.
Cores more than about 13 meters from the bottom are clear. (Photos by
Buford Price/UC Berkeley)

[Image 2:
http://www.berkeley.edu/news/media/r...thane_cell.jpg
(20KB)]
A microbe from deep in Greenland ice in the process of dividing.