A team of scientists claims they have found evidence of a water reservoir deep beneath Earth’s surface that has three times the volume of all the oceans. The Northwestern University team reports it believes this is where the seas come from. The key is a blue rock called ringwoodite, which lies in the transition zone of hot rock between the planet’s surface and core. The water is locked up in the rock about 400 miles beneath Earth’s crust, and the scientists argue it means that water on Earth may get pushed to the surface from below. This would contradict previous theories that had water reaching a younger Earth via comets. The study used earthquake data from seismometers, which showed that the melting and movement of rock in the transition zone could allow water to become fused in the rock.