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Groundwater isolated for eons

At least 1.5 billion years after it last saw the surface, flowing liquid may host life

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Drilling more than two kilometers into the ground beneath Canada, geologists have struck scientific gold: pockets of flowing water isolated underground for at least 1.5 billion years and perhaps as long as 2.64 billion years.

The water is rich in hydrogen and methane, which nourish microbes living today near hydrothermal vents on the seafloor. That means the deposits may harbor ancient lineages of life cut off from the surface for eons, the researchers report in the May 16 Nature.

Although the water has not yielded any evidence of life to date, the researchers intend to start looking. And because ancient rocks on Mars share a similar mineral composition, the finding suggests that the Red Planet could also be home to deeply buried life, says coauthor Barbara Sherwood Lollar, a geochemist at the University of Toronto.

The study “makes a good case that if there was ever a biosphere on Mars, then tiny remnants of that biosphere are very likely preserved underground,” says planetary scientist Chris McKay of NASA Ames Research Center in Moffett Field, Calif. But he doesn’t expect imminent confirmation of that proposition. “Considering that after 40 years of Mars exploration we have managed to drill only a few centimeters, it may be a long time before we can follow up on this idea.”

The discovery comes from boreholes drilled in an Ontario zinc and copper mine. The water is in fractures in rocks that were part of the seafloor roughly 2.7 billion years ago. Over time, volcanic eruptions and other geologic activity buried the rocks and trapped the water.

Sherwood Lollar and colleagues embarked on their Ontario research after discovering water in a South African gold mine that had been separated from the surface for up to 25 million years and contained microbes that were living off hydrogen and methane produced by chemical reactions between the water and rock. Some of the microbes were related to bacteria found near hydrothermal vents; others didn’t resemble any known lineages, Sherwood Lollar says.

The team searched in Ontario because of the rocks’ antiquity, but the researchers didn’t expect to find water billions of years old. “I’m not sure I believed the results to begin with,” says coauthor Christopher Ballentine, a geochemist at the University of Manchester in England.

Before the discoveries in South Africa and Canada, geologists had routinely found traces of ancient water trapped in microscopic bubbles in minerals. But researchers had never found flowing water that old. Sherwood Lollar doesn’t know how much water is trapped deep in the crust at the Canadian site. But at one of the boreholes, water flowed up over several years at rates as high as 400 milliliters per minute. 

The researchers determined the water’s age through several analyses of noble gases dissolved in the fluid. For example, the composition of different xenon forms, or isotopes, matched the expected mix in Earth’s early atmosphere.

The water was probably preserved because this region of Canada has experienced little tectonic activity that would disturb rocks, Ballentine says. Similar pockets of water might exist in any rocks this ancient, which occur worldwide, adds Steven Shirey, a geochemist at the Carnegie Institution for Science in Washington, D.C. “That’s what’s so exciting,” he says. “If it could happen here, it could happen any place.”

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