WASHINGTON –– Bacteria and algae frozen for more than 2,800 years in ice capping an Antarctic lake returned to life after thawing in a laboratory in a study that may be a dress rehearsal for searching for life on Mars.
A research team led by Peter Doran of the University of Illinois at Chicago drilled through more than 39 feet of ice to collect samples of microscopic bacteria and algae from an Antarctic feature called Lake Vida.
"When we brought them back and warmed them up a bit, they sprang back to life," said Doran, the first author of a study appearing this week in the Proceedings of the National Academy of Sciences.
Doran said the microbes have been age-dated at 2,800 years old, but even older microbes may live deeper in the ice sheet sealing Lake Vida, and in the briny water below the ice.
That deeper ice and the water itself will be cautiously sampled in a later expedition that will test techniques that may one day be used on Mars, a frigid planet thought to have subsurface lakes of ice.
The three-square-mile Lake Vida is one of a series of lakes located in the McMurdo Dry Valleys of Antarctica, some 2,000 miles due south of New Zealand.
"This lake has been known since the 1950s, but people ignored it because they thought it was just a big block of ice," said Doran. While at the site for other research in the 1990s, Doran and his colleagues sent radar signals into the clear ice covering the lake and were surprised to find that 62 feet below there was a pool of liquid water that was about seven times more salty than seawater.
That prompted the researchers to return in 1996 with equipment to drill a hole down to within a few feet of the water layer. At the bottom of this hole, they harvested specimens of algae and bacteria.
Doran said the researchers halted drilling at 39 feet to preserve an ice shell over the surface of the ancient lake.
"We haven't broken the ice seal (over the water) yet," said Doran. "We don't want to disturb that environment until we're ready."
The researchers will return in 2004 equipped with instruments that are sterilized. They will then drill through the full 62 feet of ice and sample some of the briny water from the lake for analysis. The water specimen will be cultured to see if it contains life.
Specimens from the water are expected to be even older than the life forms extracted from the ice covering.
Doran said the researchers will suck up samples of the water into a sealed airlock.
"We don't want to contaminate the lake," he said. "If we find life in the lake, we want to make sure it was living in the lake and not on our instruments."
The new study is being funded by the National Aeronautics and Space Administration because the space agency is anxious learn how best to search for life in submerged pools of briny water, said Doran, noting that Lake Vida may be an Earthly version of water deposits thought to exist on Mars.
"There is evidence of flow features on Mars made within the last million years," said Doran. "Some kind of fluid seeping out. One theory is that it could be pockets of brine like the one in Lake Vida that will not freeze because they are so salty."
Mars, thought to be one of the most likely places for life elsewhere in the solar system, is a place of deep cold, said Christopher P. McKay, a planetary researcher at NASA's Ames Research Center in Moffett Field, Cal.
"For this reason, studies of how liquid water can persist in cold environments is relevant to the search for life," said McKay in an e-mail. "Vida shows us a new way in which ice, salt and water can combine to allow liquid water habitats ... suitable for life to persist."
Doran said water flows into Lake Vida during some Antarctica summers, but the new water stays on top of the ice, sealing the lake.
"In warm summers, you get a lake on top of a lake – a one meter of water sitting on top of 19 meters of ice," he said. "That freezes over the winter and you get a buildup year after year."
Salt is expelled as the water turns to ice and is concentrated below, said Doran. Over many thousands of years, the salt concentrates in the water, making the water increasingly difficult to freeze. He estimated that water just below the ice may have a freezing point of minus 10 degrees.
"If we do find life in that water, it will be from one of the most extreme environments on Earth," said Doran. He noted the water is not exposed to the air, receives no sunlight, has a very low temperature and a high salt content.
For life to exist there, he said, it would have to get its energy from chemicals in the water, not directly or indirectly from sunlight as do most known life forms.
Searching for such extreme life forms in Lake Vida, said Doran, will be good practice for humans who one day will search for evidence of life on Mars.
"I see Lake Vida as being like life's last romp on Mars, potentially in an ice-sealed lake," he said.