In satellite images, the 20-odd coral atolls of the Maldives look something like skeletal remains or chalk lines at a crime scene. But these landforms, which circle the peaks of a mountain range that has vanished under the Indian Ocean, are far from inert. They’re the products of living processes—places where coral has grown toward the surface over hundreds of thousands of years. Shifting ocean currents have gradually pushed sand—made from broken-up bits of this same coral—into more than 1,000 other islands that poke above the surface.