Researchers at Northwestern University have found evidence for a massive reservoir of water deep within the Earth’s mantle. The reservoir, which is said to be three times the volume of the oceans on the surface, is contained within highly-pressurized rock known as ringwoodite. The scientists hope that their findings, recently published in the journal Science, can shed light on where Earth’s oceans came from.
The team, led by mineralogist Steven Jacobsen, used an array of 2000 seismometers to study how seismic waves generated by earthquakes move through the Earth’s interior. The waves’ speed changed depending on the type of rock they pass through, and wet ringwoodite has a particular effect on wave velocity. Jacobsen was able to reproduce wet ringwoodite in his lab, and the group’s findings matched what he observed in the lab. As it turns out, ringwoodite, under the extreme heat and pressure of the mantle, bleeds water. That water would then become trapped in the transition zone at between roughly 200 and 400 miles underground.
The new research lends credence to theories that our oceans originated on Earth. However, more tests will need to be conducted moving forward. Jacobsen’s team could only verify that the reservoir exists below the continental United States, so it’s unclear how far this “ocean” extends.