Did you know there’s an enormous ocean lurking beneath the Earth’s surface, deep enough that we’re only starting to uncover its secrets? It’s not a typical ocean you can sail on, but rather a hidden reservoir of water trapped hundreds of miles below the Earth’s crust—around 400 miles down.

Here’s the wild part: scientists think this "subterranean ocean" holds three times the amount of water as all the surface oceans combined. But instead of sloshing around in vast liquid form, this water is locked up in a blue mineral called ringwoodite, a sponge-like rock that traps water molecules under intense pressure.

How does this work?
The water isn't in liquid form but rather trapped within the structure of minerals in the Earth’s mantle, about 400-600 kilometers below the surface. In 2014, researchers found the mineral ringwoodite inside diamonds that had been pushed up from the mantle. When they examined it, they discovered it contained tiny amounts of water—enough to suggest there's a vast "ocean" lurking in the depths of our planet!

Why does this matter?
This underground ocean plays a key role in our planet’s water cycle—recycling water between the surface and deep interior over millions of years. Some scientists even speculate that this reservoir may have been the original source of Earth's surface oceans.

This hidden water could play a key role in volcanic activity and tectonic plate movements. It helps keep the mantle from becoming too rigid, which is essential for Earth’s plate tectonics—think of it as a secret lubricant for our planet’s inner machinery.

Some theories suggest this hidden water may have originated from Earth's early history or even from deep space, brought by water-rich asteroids that bombarded our planet billions of years ago.