After discovering a hundreds of million-year-old ecosystem in the Italian Alps, researchers are just now realizing that there is a massive ocean hidden beneath the Earth's crust.

It turns out that there is a huge supply of water 644 kilometers underground, stored in a rock known as 'ringwoodite'.

Scientists previously discovered that water is stored within mantle rocks in a sponge-like state, which is not liquid, solid or gas, but rather a fourth state.

The scientific paper titled "Dehydration melting at the top of the lower mantle" was published in 2014 and presented the findings.

"Ringwoodite is like a sponge, absorbing water, there's something very special about the crystal structure of ringwood that allows it to attract hydrogen and trap water," geophysicist Steve Jacobsen said at the time.

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"This mineral can contain a lot of water under deep mantle conditions," added Jacobsen, who was part of the team behind the discovery.

"I think we're finally seeing evidence for an Earth-wide water cycle that could help explain the vast amount of liquid water on the surface of our habitable planet. Scientists have been looking for this deep water that missing for decades."

Scientists made the findings at the time after studying earthquakes and discovering that seismometers were picking up shock waves beneath the Earth's surface. From this, they were able to prove that water was being held in the rock known as ringwoodite. If the rock contains only one percent water, that means there is three times as much water under the Earth's surface as there is in the oceans.