Massive Underground Ocean
Scientists report that they have discovered a reservoir of water, three times the volume of the world’s oceans, 700 kilometers below ground in the Earth’s mantle.
Steven Jacobsen and his team from Northwestern University in Evanston, Illinois used 2000 seismometers to study the seismic waves generated by more than 500 earthquakes. The waves generated by the earthquakes slowed down at 700 kilometers, which would happen if they were moving through wet rock. Jacobsen suspected this might be the case – ringwoodite is a mineral that might bind up large amounts of water, which are squeezed out by the tremendous pressures at that depth.
Another scientist, Graham Pearson from the University of Alberta, earlier this year discovered the first evidence of ringwoodite from a terrestrial source (not from a meteorite). The mineral was found in a dirty diamond coughed up from the depths of the mantle by a volcano, and Peason’s team confirmed the presence of water in the mineral.
These discoveries also have implications for an important scientific question: where did Earth’s oceans come from? One hypothesis is that the oceans were fed by comets hitting the Earth after the crust had hardened. Another is that the oceans formed from water bubbling up from within the newly formed Earth. This new finding supports the bubbling up from within hypothesis. (Of course, both sources may have contributed to the Earth’s oceans.)
The finding may also explain why the volume of the Earth’s oceans have been apparently stable over billions of years, as they are in equilibrium with a larger volume of subsurface water.