Overview
Over time, sea levels rose and fell with temperature, but it was always assumed that the Earth’s total surface water was constant. Now, evidence is mounting that about 3 billion to 4 billion years ago, the planet’s oceans contained nearly twice as much water – enough to submerge today’s continents. Rocks in today’s mantle, the thick layer beneath the crust, are thought to capture the value of an ocean of water or more in their mineral structures. But early in Earth’s history, the radioactivity-heated mantle was four times as hot. Work with hydraulic presses has shown that many minerals are unable to hold as much hydrogen and oxygen at jacket temperatures and pressures. A new model of the mantle’s evolution over time, based on these results, suggests that the mantle could have contained much less water in the past. And the most likely home for that water was the surface. This flooding could have stimulated the plate tectonics engine and made life on land more difficult.