Microbes can survive trapped inside ice crystals, under three kilometres of snow, for more than 100,000 years, a new study by physicists from the University of California in Berkeley, US, has revealed.
Living bacteria in ice cores sampled at depths of four kilometres in Antarctica have been found, but scientists have argued that those microbes were contaminants from the drilling and testing of the samples in labs.
In 2005, researchers incidentally, also revived a bacterium that sat dormant in a frozen pond in Alaska for 32,000 years. Now, physicist Buford Price and graduate student Robert Rohde have found a mechanism to explain how microbes could survive such extreme conditions.
According to the duo, a tiny film of liquid water forms spontaneously around the microbe. Oxygen, hydrogen, methane and many other gases then diffuse to this film from air bubbles nearby, providing the microbe with sufficient food to survive.
This way, virtually any microbe can remain alive in solid ice, resisting temperatures down to -55 degree Celsius and pressures of up to 300 atmospheres.
The scientists say, though under such harsh conditions, the microbes won't be able to grow and reproduce, they would still be able to repair any molecular damage, keeping themselves viable for more than a thousand centuries. "It is not life as we generally think about it. They are just sitting there surviving, hoping that the ice will melt," said Rohde.
To test their hypothesis, the researchers studied ice samples taken at various depths in the Antarctic and Greenland ice sheets. They detected isolated microbes, which they say must be trapped inside ice crystals. Price said their research might bolster the case for life on Mars.
"One possible explanation for the heterogeneous distribution of methane in the Mars atmosphere would be surviving sub-surface methanogens," said Price, adding that in a previous research, he and his colleagues had discovered methanogens buried under kilometres of ice in Greenland.
The research appears in the current issue of the journal Proceedings of the National Academy of Sciences (PNAS), reports New Scientist magazine.