Is there a vast reservoir of hydrogen fuel lurking beneath the Earth’s surface?

For the past few years, companies and prospectors around the world have been hunting for underground reserves of natural hydrogen, spurred by estimates that Earth contains trillions of tonnes of the gas. If found, this geologic hydrogen could accelerate the transition away from fossil fuels. But despite a few tantalising hints that vast reserves exist, the search has largely come up short.

Until recently, most geologists…