Challenge raised to role of water in behavior of Earth’s mantle

Nature : The ability of rocks to flow is behind a range of phenomena, including plate tectonics and the convection of the mantle. To better understand rock flow, Hongzhan Fei of the University of Bayreuth in Germany and his colleagues examined individual crystals of olivine, one of the common minerals in Earth’s mantle, under pressures and temperatures similar to those at depths of 100 km to 200 km. They found that silicon was the mineral’s slowest moving atom, which the team believes is the limiting factor in the rocks’ ability to flow. The researchers found that increasing the water content did not significantly increase the silicon atoms’ movement rate, contrary to some previous studies. And it still is not clear whether silicon is actually the determining factor in rock viscosity.