Ancient Earth was an aquatic world

summary

Over time, sea level has risen and fallen with temperatures, but it has always been assumed that the Earth’s total surface water is constant. Today, it’s increasingly clear that 3-4 billion years ago, the world’s oceans contained almost twice as much water – enough to submerge today’s continents. Rocks in the present mantle, the thick layer beneath the crust, are believed to sequester the value of one or more ocean water in their mineral structures. But at the beginning of Earth’s history, the mantle, warmed by radioactivity, was four times hotter. Work using hydraulic presses has shown that many minerals would be unable to retain as much hydrogen and oxygen at mantle temperatures and pressures. A new model of the evolution of the mantle over time, based on these results, suggests that the mantle may have held much less water in the past. And the most likely focus for this water was the surface. This flood could have ignited the engine of plate tectonics and made it more difficult to start life on earth.