Is there an ocean hidden under Earth's surface? Possibly, but as water locked inside rock, not liquid.

• ✓Pearson et al. 2014, Nature — hydrous ringwoodite inclusion in diamond
• ✓Schmandt et al. 2014, Science — seismic evidence for dehydration melting

There may be an entire ocean's worth of water hidden hundreds of miles beneath your feet — and you would never find it by drilling for liquid. A 2014 study found water chemically bound inside ringwoodite in Earth's mantle transition zone, suggesting the deep mantle may hold a comparable volume of water to the oceans — bound in mineral structure, not as liquid. Ringwoodite is a rare, deep-blue mineral that only forms under the crushing pressures found roughly 400 to 660 kilometres — about 250 to 410 miles — below the surface. At those depths, water does not pool or flow. Instead, hydrogen and oxygen atoms are locked inside the crystal lattice of the rock itself, invisible, immobile, and vast in quantity. The oceans you can see may not be Earth's only reservoir — they might just be the part that leaked out.