for National Geographic News
Scientists have found a place on Earth that they believe is analogous to conditions on Mars and the Jovian moon Europa, and the site is teeming with a group of microbes that far outnumber bacteria.
The discovery supports the idea that life may exist on other planets and moons.
The site is Lidy Hot Springs, located in the Beaverhead Mountains in Idaho. Living in hydrothermal waters 660 feet (200 meters) below the surface are microscopic organisms called methanogens, which derive their energy from geothermal hydrogen and produce methane as a byproduct.
Many scientists have agreed that if extraterrestrial life does exist elsewhere in the solar system, it is probably in the form of organisms at the bottom of the food chain, which have a simple metabolism and need only hydrogen and carbon dioxide to survive.
"Those two things are very common in the universe," said Francis Chapelle of the U.S. Geological Survey in Columbia, South Carolina. "It is a kind of metabolism that can happen independent of photosynthesis."
Chapelle is co-author of a paper on the microbial community in Idaho published in the January 17 issue of Nature.
Methanogens are a part of the domain of life known as Archaea. Discovered in the 1970s, Archaea inhabit environments with harsh conditions, such as hydrothermal vents, petroleum deposits, and the digestive tracts of cows.
Archaea are genetically different from seemingly similar bacteria. Bacteria, which dominate the ecosystem, live where there is organic matter and photosynthesis. Archaea, in contrast, can live in environments lacking organic carbon.
Scientists had theorized that methanogens could exist on Earth and other planets and moons. But no place dominated by the hydrogen-loving microorganisms had ever been found on Earth.
"There is this idea that there might be these communities," said Derek Lovley, a microbiologist at the University of Massachusetts in Amherst and co-author of the paper in Nature. "People have looked for a while, but the problem is that almost everywhere there is a significant amount of organic matter."
To find an environment in which Archaea were likely to dominate, the researchers went in search of a place lacking organic carbon. They focused on the hot springs in eastern Idaho because volcanic activity had burned away most of the organic carbon that could serve as an energy source for microorganisms but the water contained high concentrations of geologically produced hydrogen.
"Lidy Hot Springs does not have organic matter," said Lovley. "The only thing there is hydrogen percolating up."
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