April 16, 2009
"Among the big questions here are 'how does an ecosystem function below glaciers?', 'How are they able to persist below hundreds of meters of ice and live in permanently cold and dark conditions for extended periods of time, in the case of Blood Falls, over millions of years?," says Jill Mikucki, lead author of the paper and research associate in the Department of Earth Sciences at Dartmouth.
These extremophiles, so-called because of their ability to live in conditions lacking warmth, light, and oxygen, survive in a briny liquid, not dissimilar from seawater, where no one would have expected life.
"This briny pond is a unique sort of time capsule from a period in Earth's history," says Mikucki. "I don't know of any other environment quite like this on Earth."
Researchers were surprised that the microbes were not wholly unfamiliar. In fact, they had many similarities to microbes found in marine environments, leading researchers, largely from Harvard University and Dartmouth College, to a novel hypothesis: these extremophiles are adapted remnants of a once larger population of ocean-dwelling microbes.
"The salts associated with these features are marine salts, and given the history of marine water in the dry valleys, it made sense that subglacial microbial communities might retain some of their marine heritage," Mikucki said.
One scenario imagines that when sea levels fell more than 1.5 million years ago, microbes were trapped in a pool of leftover seawater, which was eventually covered-over by the Taylor glacier. Most of the life-forms would have perished, but the newly-discovered microbes must have adapted quickly enough to survive in their present form.
"It's a bit like finding a forest that nobody has seen for 1.5 million years," says Ann Pearson, Thomas D. Cabot Associate Professor of Earth and Planetary Sciences at Harvard. "Intriguingly, the species living there are similar to contemporary organisms, and yet quite different -- a result, no doubt, of having lived in such an inhospitable environment for so long."
Chemical analysis has shown that the microbes likely survived by breathing iron with the aid of sulfur catalyst. Since there was no sunlight for photosynthesis, the researchers believe the microbe survive by feeding off organic material that was trapped with them 1.5 million years ago.
The Dry Valleys of Antarctica, where the microbes were found, is one of Earth’s most extreme environments. Receiving only 10 centimeters (almost 4 inches) of snow every year, this vast desert supports no complex animal or plant life. In the summer temperatures sometimes rise enough to melt water from the glaciers pushing into the valleys, such as Taylor glacier, providing new water sources to lakes and pools covered over by ice.
The discovery and analysis of these unique microbial life forms may provide insight into Earth’s past as well as possibilities of life beyond our planet. The scientists believe the microbes will provide better understanding of the Earth's geological period where ice sheets covered most of the terrestrial surface, a time aptly named “Snowball Earth”. As well, understanding these life forms may give scientists with better tools for locating life that may exist on other planets, including ice caps on Mars and one of Jupiter’s moon, Europa, which is a planetary body covered in ice.
CITATION: "A Contemporary Microbially Maintained Subglacial Ferrous 'Ocean'," by J.A. Mikucki; A. Pearson; D.T. Johnston; D.P. Schrag; A.V. Turchyn; J. Farquhar; A.D. Anbar; J.C. Priscu; P.A. Lee. Science, Vol 324. April 17, 2009.
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