Earth may have cooked up its own oceans as it grew, experiments suggest

Where did Earth's water come from? The usual story imports it — delivered by icy comets and meteorites from far away. A University of New Mexico team, led by graduate student Susmita Garai with professors Zachary Sharp and Peter Olson, tested a homegrown alternative in Nature Geoscience: as the young Earth grew by gathering rocky pebbles, those pebbles fell through its hot, hydrogen-rich atmosphere, and the iron oxide in the rock reacted with hydrogen to make metallic iron and water vapour. In their high-temperature experiments, nearly 80% of the iron oxide converted — producing water in minutes. Extrapolating, they estimate hundreds of oceans' worth could have formed this way. 'Virtually any Earth-sized planet should have water by this newly identified mechanism,' Sharp said — which would make habitable worlds a common outcome, not a lucky delivery.