A vast reservoir of water has been discovered 400 miles beneath the Earth's surface, not in liquid form, but stored within a rock called ringwoodite. This groundbreaking discovery, detailed in the 2014 paper 'Dehydration melting at the top of the lower mantle,' reveals a sponge-like state of water within mantle rock.
Geophysicist Steve Jacobsen explained that ringwoodite's unique crystal structure attracts and traps hydrogen, allowing it to hold substantial amounts of water under deep mantle conditions. Scientists made this discovery by studying earthquakes and analyzing shockwaves detected by seismometers.
The findings suggest the existence of a whole-Earth water cycle, potentially explaining the abundance of liquid water on our planet's surface. If ringwoodite contains just 1% water, the underground reservoir would hold three times more water than all the Earth's oceans combined.