Spongy clay might create huge water deposits deep inside Earth

We might finally know how ocean-sized deposits of water hundreds of kilometres below Earth’s surface are getting there. A form of clay, called kaolinite, might be soaking up water like a sponge and bringing it deep underground.

Depending on the location, kaolinite accounts for between 5 and 60 per cent of ocean sediment . Now, geologists have demonstrated how it can act as an irrigation system for the upper mantle, the mineral and rock layer that descends to more than 400 kilometres beneath our feet.

The clay gets…