Vast quantities of water inside the Earth?

A small, battered diamond found in the gravel strewn along a shallow riverbed in Brazil has provided evidence of a vast "wet zone" deep inside the Earth that could hold as much water as all the world's oceans put together. The water is not sloshing around inside the planet, but is held fast within minerals in what is known as the Earth's transition zone, which stretches from 410 to 660km (250-400 miles) beneath the surface.
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