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Title: Microbes Can Survive 'deep Freeze' For 100,000 Years
URL: http://space.newscientist.com/article/dn12752-microbes-can-survive-dee
p-freeze-for-100000-years.html
Date: 10/08/2007
Publication: New Scientist
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Microbes can survive trapped inside ice crystals, under 3 kilometres of snow, for more than 100,000 years, a new study suggests. The study bolsters the case that life may exist on distant, icy worlds in our own solar system.

Living bacteria have been found in ice cores sampled at depths of 4 kilometres in Antarctica, though some scientists have argued that those microbes were contaminants from the drilling and testing of the samples in labs. And in 2005, researchers revived a bacterium that sat dormant in a frozen pond in Alaska for 32,000 years (see Ice age bacteria brought back to life).

Now, physicist Buford Price and graduate student Robert Rohde, both at University of California in Berkeley, US, have found a mechanism to explain how microbes could survive such extreme conditions.

They say a tiny film of liquid water forms spontaneously around the microbe. Oxygen, hydrogen, methane and many other gases will then diffuse to this film from air bubbles nearby, providing the microbe with sufficient food to survive.

Thus, virtually any microbe can remain alive in solid ice, resisting temperatures down to -55 Celsius and pressures of 300 atmospheres.

Under such harsh conditions, the microbes would not be able to grow and reproduce, but they would still be able to repair any molecular damage, keeping themselves viable for more than a thousand centuries, the team says. "It is not life as we generally think about it," says Rohde. "[They] are just sitting there surviving, hoping that the ice will melt."

To test their hypothesis, the researchers studied ice samples taken at various depths in the Antarctic and Greenland ice sheets. They detected isolated microbes that they say must be trapped inside ice crystals.

Survival strategy

Price says the new work may bolster the case for life on Mars. Methane breaks down relatively quickly when exposed to sunlight, so when it was discovered in the Martian atmosphere in 2004, some scientists suggested that methane-producing microbes, or methanogens, might be continually producing more of the gas.

"One possible explanation for the heterogeneous distribution of methane in the Mars atmosphere would be surviving sub-surface methanogens," Price told New Scientist, adding that he and colleagues had previously found methanogens buried under kilometres of ice in Greenland.

Astrobiologist Dirk Schulze-Makuch of Washington State University in Pullman, US, says he doubts that any such microbes could produce enough methane to explain the detections on Mars.

But he says the diffusion mechanism identified in the new work does boost the chances for extraterrestrial life. "The main reason for this is that most of the planets and moons in our solar system are icy worlds," he told New Scientist. "Thus any type of survival mechanism and possible avenue for metabolism in cold and very cold environments would be a great evolutionary trait for any organism on an icy world."

John Priscu of Montana State University in Bozeman, US, agrees. "We have another mechanism of life support in an environment that would otherwise seem to be inhospitable," he told New Scientist.

Astrobiology learn more in our out-of-this-world special report.

Journal reference: Proceedings of the National Academy of Sciences (doi: 10.1073/pnas.0708183104)