After decades of theorizing and searching, scientists are reporting that they’ve finally found a massive reservoir of water in the Earth’s mantle — a reservoir so vast that could fill the Earth’s oceans three times over. This discovery suggests that Earth’s surface water actually came from within, as part of a “whole-Earth water cycle,” rather than the prevailing theory of icy comets striking Earth billions of years ago. As always, the more we understand about how the Earth formed, and how its multitude of interior layers continue to function, the more accurately we can predict the future. Weather, sea levels, climate change — these are all closely linked to the tectonic activity that endlessly churns away beneath our feet.