This is the kind of research that deserves attention! Recently published in Science, scientists have discovered a vast ocean trapped in a mineral called ringwoodite about 660km below the earth's surface.
It suggests that the water forming Earth's oceans may have come from deep within the planet, and then pushed towards the surface due to geological processes, rather than being deposited by icy comets.
This has huge implications for our knowledge of the planet, particularly for topics such as water security (suggesting of course that we will at some point get our hands on it and not cause the planet to implode as a result).
Jacobsen and his colleagues are the first to provide direct evidence that there may be water in an area of the Earth’s mantle known as the transition zone. They based their findings on a study of a vast underground region extending across most of the interior of the US. Ringwoodite acts like a sponge due to a crystal structure that makes it attract hydrogen and trap water. If just 1% of the weight of mantle rock located in the transition zone was water it would be equivalent to nearly three times the amount of water in our oceans, Jacobsen said.