Barbara Sherwood Lollar, geologist at the University of Toronto, crouches over a bubbling upwelling of very clear water from a fracture on the floor of a 3 km deep mine in the Canadian Precambrian Shield near Timmins, Ontario. She dips her finger in the pool and brings it to her mouth for a taste. “Very salty,” she says. “much saltier than seawater.”
It turns out that the saltier the water, the older it is likely to be. The taste test is the first step to further analysis that uses oxygen and hydrogen in the water molecule, as well as noble gases such as helium, neon, argon and xenon, and presence of certain isotopes created early in Earth’s history through interactions with the surrounding radioactive rock. Analysis reveals that the hydrogen-rich water Sherwood Lollar tasted is between 1.5 and 2.6 billion years old—as old as the rocks themselves. The hydrogen- and methane-rich water may provide energy for microbes like those found around hydrothermal vents in the deep ocean. “When these rocks formed,” Sherwood Lollar shares, “this part of Canada was the ocean floor.”
Geologists have known since the 1880s about the presence of deep salty ancient water in continental crust—locked in microscopic voids in minerals, pore spaces between minerals, and veins and fractures in rock—in Canada, Finland and South Africa. The question had been: is that water part of current circulation with surface water or does it retain old chemistry, structure and potential biota? These new findings, reported in the journal Nature in May 2013, provide evidence that ancient pockets of water have remained isolated in the Earth’s crust for billions of years.
This ancient water provides an “energy that can support life without sunlight,” says Lollar. Instead, the microbes would subsist on chemicals created through the interactions between water and rock. A decade earlier in a South African gold mine some 2.8 km below the surface, Lollar and others discovered sulfate-reducing microbial communities in saline fracture waters. The microbes survived, cut off from the sun for tens of millions of years.
Two chemical reactions combine to produce high quantities of hygrogen—the most common substance in the universe—and doubling estimates of global production from these processes. Previous estimates had been based on hydrogen production from the ocean floor. “This represents a quantum change in our understanding of the total volume of Earth’s crust that may be habitable,” said Sherwood Lollar.
Estimates had not previously included contributions from the ancient continents such as Precambrian rocks, which comprise more than 70% of the surface of the Earth’s crust. This is a huge source of possible energy for life and has important implications for the search for deep microbial life and for astrobiology.
Large areas on Mars resemble the Earth’s Precambrian Shield, with billions of years-old rocks of similar mineralogy. If the ancient rocks of Earth are producing this much hydrogen, similar processes may be occurring on Mars, said Sherwood Lollar.
“Life that formed could have found its way into similar pockets of water in the Martian crust,” Chris Ballentine, geochemist at the University of Manchester, said. “These pockets of water can survive and provide a place for life to have survived long after the surface of Mars lost its water and became sterile.”