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.
