Scientists discover a hidden ocean 700 kilometres beneath Earth that may be bigger than all oceans

Scientists have identified evidence of a vast water reservoir about 700 kilometers beneath Earth’s surface, locked within the mineral ringwoodite in the mantle’s transition zone. This “hidden ocean” isn’t liquid like surface seas but water molecules trapped in the rock’s crystal structure, potentially holding three times the volume of all Earth’s surface oceans combined.

Researchers detected it indirectly through seismic waves from earthquakes, which slow down in water-rich areas, and lab experiments replicating mantle conditions. The finding, first detailed in a 2014 Science study and revisited in recent reports, challenges ideas about Earth’s water origins.

This reservoir suggests water may have seeped from Earth’s interior to form surface oceans over billions of years, rather than arriving solely via comets. It could influence mantle convection, volcanism, and the planet’s long-term water cycle.