A huge "wet zone" hundreds of miles beneath the surface of the Earth could hold as much water as all the oceans put together, according to researchers analyzing a mineral from deep in the mantle. The water is "not a Jules Verne-style ocean you can sail a boat on," explains one of the authors of a study in the journal Nature, but is held inside minerals in the "transition zone" 250 to 400 miles underground. Researchers believe the water ended up deep underground as slabs of ocean crust sank into the mantle, reports LiveScience, though it could also be "primordial" water brought long ago by asteroids or comets.
Evidence of the vast reservoir was provided by a water-rich sample of ringwoodite, a mineral that exists deep inside the mantle but has only ever before been seen in samples created in labs or extracted from meteorites. It was found in a battered diamond dug up by miners in Brazil. "It's a fairly ugly diamond. It looks like it's been to hell and back," the lead researcher says, according to the Guardian. The diamond was brought to the surface from hundreds of miles underground by a violent volcanic eruption researchers say was "analogous to dropping a Mentos mint into a bottle of soda." (Another fascinating recent discovery: an ancient ocean ... preserved underneath the Chesapeake Bay.)