How much hydrogen awaits us underground?

In the 1990s, Barbara Sherwood Lollar descended into the Kidd Creek mine in northern Ontario, which cuts more than three kilometers into the ancient root of North America. There her team of geochemists found water that had been confined underground for more than a billion years. This ancient brine turned out to be a habitat for living microbes that feed on the hydrogen produced in reactions between the water and the rock.

Decades later, Sherwood Lollar, who is a geochemist at the University of Toronto, revisited the team’s hydrogen data to see if there is enough of the gas in the mine to make it a useful source of zero-carbon fuel. “If we can set some smart minds into figuring out how to hook it up and use it, then we’ve got a win for this nascent economy,” she says.

While hydrogen fuel does show promise as a versatile power source, producing it typically generates lots of greenhouse-gas emissions and requires more energy than the gas contains. The ability to tap ready-made underground reservoirs—so-called “geologic hydrogen”—would change the equation.

A flurry of exploration efforts have launched to search for the stuff, which is produced underground when water molecules are split by chemical reactions with iron-rich rock or—as they are at Kidd Creek—by the radioactive decay of other elements. The hunt has spread all over the world and engaged dozens of startups, including the Australian firm HyTerra and the Bill Gates–backed company Koloma, which have both been poking around the US Midwest to reach ancient oceanic rocks associated with hydrogen production.

Researchers at the US Geological Survey have estimated that trillions of tons of H 2 are produced within Earth’s crust; if a small fraction of this could be recovered, it could meet global hydrogen demand for centuries. But the search so far has come up short. No one has yet reported finding a commercially viable reservoir of the gas, and public data on what has been found remains in short supply as companies jockey for position and seek to attract investment.

At Kidd Creek mine, Sherwood Lollar and her colleague Oliver Warr leveraged their long-term record of hydrogen to get a fresh read on the potential. By scrutinizing data they’d collected from 35 boreholes at the mine over more than a decade, they found that each one consistently released an average of eight kilograms of hydrogen per year. Extrapolating that finding to the more than 14,000 boreholes at Kidd Creek would mean that around 140 metric tons of the gas is flowing unused out of the mine’s vents each year.

This tally, published earlier this year in the journal PNAS , is not a world-changing amount, but Sherwood Lollar says that if all the hydrogen could be captured, it would offer at least a modest source of energy—perhaps enough to power a substantial portion of the mine’s operations. That would be a valuable local demonstration that geologic hydrogen really can be put to use, she says.