Across the ages, sea levels have risen and fallen with temperatures—but Earth’s total surface water was always assumed to be constant. Now, evidence is mounting that some 3 billion to 4 billion years ago, the planet’s oceans held nearly twice as much water—enough to submerge today’s continents above the peak of Mount Everest. The flood could have primed the engine of plate tectonics and made it more difficult for life to start on land.
Rocks in today’s mantle, the thick layer of rock beneath the crust, are thought to sequester an ocean’s worth of water or more in their mineral structures. But early in Earth’s history, the mantle, warmed by radioactivity, was four times hotter. Recent work using hydraulic presses has shown that many minerals would be unable to hold as much hydrogen and oxygen at mantle temperatures and pressures. “That suggests the water must have been somewhere else,” says Junjie Dong, a graduate student in mineral physics at Harvard University who led a model, based on those lab experiments, that was published today in AGU Advances. “And the most likely reservoir is the surface.”
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