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 jo