Scientists have found life in an Antarctic lake that was sealed off from the outside world by a thick sheet of ice several thousands of years ago.
Brine collected from boreholes drilled into Lake Vida contains scores of bacteria that clung on to life despite making their home in one of harshest environments on Earth.
The lake lies in a barren region called the McMurdo Dry Valleys, in the east of the continent.
The water in Lake Vida is acidic, starved of oxygen, and so salty that it remains liquid despite its temperature hovering around the -13°C mark all year round.
Researchers identified organisms from eight major groups of bacteria, among them common forms such as proteobacteria, firmicutes and bacteroidetes. Another group, the verrucomicrobia, are named for their wart-like bulges.
The discovery of the ecosystem pushes the boundaries of what life can endure, and may inform the search for alien microbes on other planets, such as Mars, or on icy moons such Jupiter's Europa.
In a previous expedition, scientists extracted cores from the slab above Lake Vida and dated organic material inside to around 2,800 years ago.
The lake has been cut off from the outside world for at least that long, meaning organisms that live there have evolved in isolation for millennia.
Writing in the journal Proceedings of the National Academy of Sciences,Alison Murray at the Desert Research Institute in Reno, Nevada, describes Lake Vida as "a potential analogue for habitats on other icy worlds".
Tests on the brine revealed high levels of nitrous oxide and also molecular hydrogen, which is formed by two hydrogen atoms joining together.
The chemicals are thought to be released from chemical reactions between the brine and underlying sediments.
The molecular hydrogen may be crucial as an energy source for life in the lake.
"Lake Vida is an incredibly harsh environment. It has not been exposed to the surface for thousands, if not millions, of years," said Mike Bentley, a professor of geology at Durham University. "If you understand life in extreme environments, you understand life better: it tells you what the controls are on life."
Bentley is one of a team of scientists who this year will drill into Lake Ellsworth, which lies under 3km of glacier in West Antarctica.
"If we find no life in Lake Ellsworth, that tells us that although we've found life in deep water before, and we haveve found it in the cold and in the dark before, putting all those together with isolation might be enough to stop life occuring," Bentley said.
"In Antarctica, its not the cold that is the problem: it's the availability of water. You can survive at -50°C temperature , and as long as there are tiny amounts of liquid water, life will usually find a way to survive," Bentley added.
Guardian News Service