Evolution of (a) mantle temperature and (b) viscosity fora terrestrial planet with Earth-like composition (Mg/Si = 1.2, 8 wt% FeO) as a function of pressure (GPa), ranging from the surface (0 GPa) to the core–mantle boundary (138 GPa, 2891 km). In panel a, the solidus and liquidus from Andrault et al. (2011) are shown as thin black lines that bound a grey area; the temperature profile of the modern Earth is shown as a thick black line (Stacey & Davis 2008).