Credit: Zoë van Dijk

Alexis Templeton remembers January 12, 2014, as the day the water exploded. A sturdy Pyrex bottle, sealed tight and filled with water, burst like a balloon.

Templeton had just guided her Land Cruiser across the bumpy, rock-strewn floor of Wadi Lawayni, a broad, arid valley that cuts through the mountains of Oman. She parked beside a concrete platform that rose from the ground, marking a recently drilled water well. Templeton uncapped the well and lowered a bottle into its murky depths, hoping to collect a sample of water from 850 feet below the surface.

Wadi Lawayni is enclosed by pinnacles of chocolate-brown rock, hard as ceramic yet rounded and sagging like ancient mud-brick ruins. This fragment of the Earth’s interior, roughly the size of West Virginia, was thrust to the surface through an accident of plate tectonics millions of years ago. These exotic rocks—an anomaly on Earth—had lured Templeton to Oman.

Shortly after she hoisted her sample from the well, the bottle ruptured from internal pressure. The water gushed out […]