One and a half miles beneath the surface of Earth in a Canadian mine, researchers have found pockets of water in rocks that have been isolated from the surface for some two billion years.

The chemistry of the water could support life, the team reports today in the journal Nature -- a tantalizing discovery that raises the possibility that life-supporting water might also lie in similar kinds of rocks deep beneath the surface of Mars.

Because the water was trapped at a time when Earth was very different than it is today, the new findings also lend insight into the evolution of the early atmosphere and the habitability of the deep Earth. Until now, the oldest known reservoirs of underground water dated back just tens of millions of years.

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"For the first time, we found that waters of this age can be preserved on our planet," said Barbara Sherwood Lollar, an isotope geochemist at the University of Toronto. "Really, it's a whole new world, a whole new hydrosphere on our planet. We didn't know it was possible to trap this amount of fluid and gas for this kind of time scale."

Miners have long known that water sometimes flows out of fractures in rocks deep underground, Sherwood Lollar said. As scientists have more recently become interested in the phenomenon, they have discovered that these fluids are often very salty, with salinity levels 10 times higher than seawater.

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Deep isolated waters also contain large amounts of dissolved hydrogen, making it possible that they might sustain microorganisms like the ones that live around hydrothermal vents. In 2006, in fact, Sherwood Lollar and colleagues found a community of microbes living deep below South Africa in isolated waters that were tens of millions of years old.

"I refer to hydrogen as the jelly donuts of the microbe world," Sherwood Lollar said. "If it's there, they want to eat it."

Billion-year-old sparkling water being collected. J. Moran (2009)

For the new study, the researchers lowered a tube-shaped device into pre-drilled boreholes in a mine in Ontario. Water flowed through the device, which separated the gas from the fluid and collected both.

In laboratories in Canada and the United Kingdom, scientists then measured levels of hydrogen, carbon, nitrogen and other stable elements as well as noble gasses such as helium, xenon and krypton. Knowing how quickly chemical reactions proceed over time between rocks and water, the team could then use the levels of those components to determine how long the fluid had been trapped in the deep crust.

Results showed that the water was between one billion and 2.6 billion years old -- orders of magnitude older than the South African samples.

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The water dates back to a time before the Great Oxygenation Event that filled Earth's atmosphere with oxygen, making it possible for higher life forms to evolve, said planetary scientist Michael Mumma, director of the Goddard Center for Astrobiology at the NASA Goddard Space Flight Center.

Now, the search is on for signs of life in the ancient Canadian waters. If microbes turn up there and they are as old as the water is, the discovery could offer new places to look for life on Mars, which has rocks of similar age to those looked at in the new study.

"I think this is quite a profound finding," Mumma said. "In a similar environment, a tectonically quiet environment on Mars, such reservoirs of these trapped gasses could in fact host a population of microbes of similar nature. And we could still find evidence that they were there at one time or in fact still do exist."