Scientists have discovered a massive reservoir of water 400 miles below the United States.
The discovery appears to confirm that water actually filters through the Earth, from the oceans, collecting in vast reservoirs under the surface.
The evidence suggests that water molecules become trapped inside the minerals of mantle rock found deep below the Earth's surface, and then gradually cycle back up due to plate tectonics.
Discovered by geophysicist Steve Jacobsen and University of New Mexico seismologist Brandon Schmandt, the huge reservoir could help scientists better learn how the Earth was formed.
Speaking to phys.org, Jacobsen explains the significance of their findings:
"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. Scientists have been looking for this missing deep water for decades."
Interestingly this isn't a reservoir in the conventional sense; there isn't a vast floating ocean underneath America. And no, there are no dinosaurs wandering its shores.
Instead the water is trapped inside the molecular structure of minerals found within the mantle rock.
Incredibly if just 1% of the Earth's mantle rock contained H2O that would amount to three times the amount of water that's in our oceans.
The theory was first postulated when a mineral called ringwoodite was discovered as part of a volcanic eruption in Brazil.
It's believed the mineral was brought up from a depth of around 400 metres below the Earth's surface. What scientists found when they analysed it was a surprising amount of water was actually trapped inside.
"The ringwoodite is like a sponge, soaking up water, there is something very special about the crystal structure of ringwoodite that allows it to attract hydrogen and trap water. This mineral can contain a lot of water under conditions of the deep mantle."
To give you some idea of just how little we know about our own planet, that sample of ringwoodite is the only known sample of it to have come from within the Earth.