Scientists have found evidence of a huge underground reservoir containing up to three times as much water as on the entirety of the earth’s surface and theorized to be the source for all the world’s oceans.

The new evidence, published Friday in the journal Science, suggests that melting rocks, including those containing the water-rich mineral ringwoodite, may exist far deeper below the earth’s surface. The discovery suggests to researchers that most of the earth’s water seeped out from within, as opposed to arriving on ice-bearing comets, a theory many scientists have posited.

“I think we are finally seeing evidence for a whole-earth water cycle, which may help explain the vast amount of liquid water on the surface of our habitable planet,” said Steve Jacobsen, a Northwestern University professor and a co-author of the study. “Scientists have been looking for this missing deep water for decades.”

H and his fellow researchers studied data from a network of seismometers placed around the U.S. called USArray, as well as lab experiments that simulated what materials like ringwoodite can do at high pressure.

The seismometers measured the speed of shock waves caused by earthquakes. Scientists could tell when a wave hit a liquid layer because the waves slow down as they pass through the viscous water.

Ringwoodite, a mineral spread throughout the earth’s mantle (the zone between the earth’s surface and its core) has a crystalline structure that attracts hydrogen and thus can act as a massive sponge for water.

While ringwoodite has been known for years to attract water, Jacobsen’s study is the first to show that it may be holding such vast stores of water far beneath the earth’s surface.

The findings back up another study from March, which focused on a diamond found 400 miles below the earth's surface that was discovered to contain ringwoodite; to date, it’s the only ringwoodite that was taken directly from the earth and not synthesized in a lab. It was found to contain a remarkable amount of water for such a small sample.

Jacobsen's study suggests that the movement and melting of rocks containing water-rich ringwoodite could produce water capable of seeping out to the surface. Jacobsen said that if just 1 percent of the mantle’s mass is water, that would be nearly three times as much water as in all the oceans.

Jacobsen and his team studied only rock beneath the U.S. He said he wants to expand their study around the world to show that ringwoodite and its water are indeed a worldwide phenomenon.

Al Jazeera