for National Geographic News
Some years ago, researchers found something that sent shivers through the scientific community: a diverse community of microbial life-forms that live without sunlight or a ready supply of nutrients.
The scientists were not searching deep space when they made their find. Rather, they were sampling the bottom of a 2.5-mile-thick (4-kilometer-thick) Antarctic ice sheet.
The frozen mass covers Lake Vostok, a freshwater lake. Scientists demonstrated that the bottom layer of the ice sheet, the same one that contained the microbial life-forms, was composed of accreted, or frozen, lake water.
This, in turn, led scientists to suggest that a large, diverse community of microbes lived in the lake itself. If true, the theory would answer questions about the limits of life on Earth and expand the range of environments that might potentially host life-forms in space.
Two independent research teams announced the initial discovery of the Antarctic ice sheet microbes in the December 10, 1999, issue of the journal Science.
One study was led by John Priscu, an ecologist with the Department of Land Resources and Environmental Sciences at Montana State University in Bozeman. The other by David Karl, a microbial biologist with the School of Ocean and Earth Science and Technology at the University of Hawaii in Honolulu.
Since then the research teams and others have further analyzed the microbes. They've sought to describe the microbes' diversity and to determine whether or not the microbes might actually be contaminants introduced to ice-core samples by the instruments used to gather and study them.
According to Priscu, new data gathered by his team shows that the microbes have diverse physiologies. The data also suggest that Lake Vostok hosts the life-forms in high abundance, he said.
"I believe there are about 10,000 [microbial] cells per milliliter [0.2 teaspoon] in Lake Vostok surface water, which is about a hundred times lower than that typical in the open ocean," Priscu said.
Karl's team has also conducted further analysis and found that a viable microbe population lives in the Antarctic lake buried under miles of ice. Although Karl noted that "the biomass may be very low."
Other scientists, however, have disputed the initial findings of both research teams, suggesting that it was the instruments used to retrieve and study the ice core samples that were contaminated with microbesnot the the bottom layer of the ice sheet. (See sidebar.)
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