Earth may have a massive “ocean” in the mantle

New Scientist : A volume of water three times that of all Earth’s oceans combined may reside in Earth’s mantle in a type of rock called ringwoodite. “It’s rock with water along the boundaries between the grains, almost as if they’re sweating,” according to Steven Jacobsen of Northwestern University. Jacobsen and coworkers discovered the possible water reservoir by studying the seismic waves generated by more than 500 earthquakes. Because seismic waves travel more slowly through wet rock than dry rock, the researchers were able to determine that there were sizable deposits of water-soaked ringwoodite in Earth’s transition zone, which lies between the lower and upper mantle. If so, such an underground reservoir would indicate that Earth’s water came from within rather than being brought by ancient comets, as previously proposed. It would also explain how the oceans have stayed the same size for millions of years.

Updated (12 June 2014) - The original title of this post has been changed from “Earth may have massive ocean at its core” to more accurately reflect the finding of water bound to minerals in Earth’s mantle.