Pressure dependence of viscosity, or is the earth's mantle a glass?

Little is known about the real conditions in the earth’s interior because direct sampling is not feasible. The propagation of seismic waves is the only instrument for investigating the mantle. Therefore, viscosity η is of prime importance. Experimental data indicate that mantle viscosity is about 1022 Pa s. At such a high viscosity even molten materials behave like solids. The aim of the present paper is to demonstrate that, due to the extreme pressure, viscosity increases sharply. In this way the glass transition temperature increases faster than the melting point, so an important part of the mantle could be in a glassy state, although being molten. (Some figures in this article are in colour only in the electronic version)