Earlier this year we reported that vast oceans of water could be hiding under the earth’s mantle. Now this theory has more support as scientists have discovered a rare diamond which hints at a great "wet zone" far down within the Earth that might hold as much water as all the world’s oceans put together. "Writing in the journal Nature, scientists said they had found an elusive mineral pointing to the existence of a vast reservoir deep in Earth’s mantle, 400 to 600 kilometres beneath our feet."