Water content plays a vital role in determining mantle rheology and thus mantle convection
and plate tectonics. Most parameterised convection models predict that Earth initially
underwent a period of rapid degassing and heating, followed by a slow and sustained
period of regassing and cooling. However, these models assume water is instantaneously
mixed and homogeneously distributed into the mantle. This is a limitation because the
mixing time for water entering and leaving the mantle is a function of the Rayleigh number …

MgO makes up about 20% of the Earth's lower mantle; hence, its rheological behaviour is
important for the dynamics and evolution of the Earth. Here, we investigate the strength of
twin boundaries from 0 to 120 GPa using DFT calculations together with structure prediction
methods. As expected, we find that the energy barrier and critical stress for shear-coupled
migration of the 310/[001] interface vary strongly with pressure. However, what is surprising
is that the twin boundary also exhibits sudden strong discontinuities in strength which can …