A HOT layer of rock deep underground could be hiding five times as much water as is held in all Earth鈥檚 oceans.
Planetary scientists believe that when the Earth formed, about 2 per cent of its mass would have been water. Yet today鈥檚 oceans hold only a hundredth of that. No one knows if the rest escaped or is locked away under the surface.
Motohiko Murakami of the Tokyo Institute of Technology looked at the lower half of the Earth鈥檚 mantle. It was thought to contain very little water, but Murakami鈥檚 group found that defects in the rock formed by aluminium and iron impurities could hold enough water to make up 0.2 per cent of the lower mantle鈥檚 mass鈥攆ive times as much water as the oceans store (Science vol 295, p 1885).
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