One morning last August, the Monterey Bay Aquarium Research Institute's deep-sea robot, named Doc Ricketts, was snooping around the ocean floor in 1,812 meters of very cold water off the coast of northern California. It was gliding over an oblong mound 2,000 meters long and 60 meters thick, draped in places with a thin layer of khaki-colored sediment. Video from the robot's underwater camera suddenly revealed what looked like a dirty yet nonetheless luminously white snowbank—the kind found at the edge of a plowed parking lot, except for the clams and fish around it. This glowing ledge showed that the mound contained methane hydrate, a lattice of frozen water that traps methane gas molecules within its icy cages. If you grabbed a snowball of the stuff, you could light it on fire.