“PEOPLE keep asking if we’ve found the water that dripped underground from Noah’s flood,” says Jesse Lawrence. No wonder: he has found a reservoir holding as much water as the Arctic Ocean deep below Earth’s surface.

Lawrence, from the University of California, San Diego, and Michael Wysession of Washington University in St Louis, Missouri, analysed more than 600,000 seismic signals generated by earthquakes travelling through the Earth. They were surprised to find that the waves weakened below eastern Asia at depths between 600 and 1200 kilometres, corresponding to Earth’s lower mantle.

The researchers realised that there must be massive …