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In what could point to the existence of life on other planets, Carolina
scientists have helped discover teeming microbe colonies beneath lake ice in
Antarctica that use sunlight filtering through the ice to activate and sustain
life when the South Pole tilts toward the sun each year.
In fact, Hans Paerl, Kenan professor of marine sciences, and other researchers
have found surprisingly diverse microorganisms throughout the frozen lake
water, supported by the key life-sustaining processes photosynthesis and
atmospheric nitrogen fixation. Previously, most investigators thought little or
no biological activity could occur within the ice itself.
"This discovery, which is quite exciting, shows how life could exist on other
planets," Paerl said. "Solar heating allows the water to melt around soil
particles that have blown over the ice and have been buried in it. Microbes
covering them can then spring to life within an hour under certain conditions,
even though they are still embedded deep in the ice."
The result, Paerl said, are living layers within the ice that distinctly show
years, like growth rings in a tree trunk. He called the layers "self-sustaining
microbial ecosystems."
"A key to the ability of microbes to live under these extreme conditions is
the presence of liquid water, which is formed by solar heating of dark,
light-absorbing soil aggregates embedded in the ice," he said.
Soil particles carried by wind from dry Antarctic valley floors onto the
frozen lakes absorb sunlight during summer in the Southern Hemisphere, warm up
and slowly melt down through the thick ice, the new studies showed. After
descending through the ice, they break through and fall to the lake floor.
"We think this work suggests that even though the ambient temperatures on
other planets are quite low, soil particles could heat up enough locally
through solar heating to support formation of liquid water, microbial growth
and reproduction," Paerl said. "Mars is a good example of the kind of place
where this might happen."
Among the microbes the scientists identified were blue-green algae, or
cyanobacteria, which are the most ancient photosynthetic, oxygen-producing
organisms known on Earth, and various bacteria, the marine scientist said.
During months of total darkness, the microscopic worlds of soil, melted water
and microbes within the ice freeze completely again to wait for the sun the
following year.
The research team carried out its experiments at Lake Bonney in the Antarctic
McMurdo Dry Valleys. A report on the findings appears in the June 26 issue of
Science. Along with Paerl, report authors are James L. Pinckney, a research
professor at the University's Institute of Marine Sciences in Morehead City,
and several scientists from around the country.
In an accompanying editorial, Roland Psenner and Birgit Sattler of Innsbruck
University say because of the new discovery, cultivating bacteria and algae in
a deep freeze is not so outrageous an idea as previously believed.
"What at the first glance appears to be a contradiction in terms (being frozen
and leading an active life at the same time) turns out to be an exciting
example of the adaptation of microorganisms to environmental extremes," they
wrote.
"What is the attraction of studying life in the cold? It may be the beauty of
simplicity, which--especially in the case of the Antarctic lake ice--promises
that sooner or later we may be able to understand and model ecosystems with
simple structures and frozen dynamics."
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