Within the Canadian Shield, hydrogen gas is steadily building up naturally among some of the oldest rocks on Earth. Geochemists at the University of Toronto and the University of Ottawa have for the first time measured its presence, mapped its concentration and tracked its long-term accumulation, shedding new light on this source of natural, or white, hydrogen. The findings demonstrate that natural H2 accumulates in substantive volumes, that it can be trapped and preserved on long time scales, and that high concentrations and discharge rates can be sustained over periods of years, making it possible to assess the economic viability of this emerging energy source and point to a new approach to hydrogen exploration — one that could accelerate greenhouse gas reductions and expand hydrogen’s role in the clean energy transition.