Extended Data Figure 4. Thermal evolution of the core and MgO exsolution rate.

(a) Example CMB temperature evolution as a function of time (after core-formation) from Fig 4a of ref. 18, and its derivative (c), which is the cooling rate. (b) The associated MgO equilibrium concentration in the core, obtained by turning the temperature dependence in Fig. 1b into time dependence; and its derivative (d) which is the exsolution rate. MgO will only start exsolving from the core when the MgO equilibrium concentration (panel b) drops below the MgO content in the core inherited from core formation and the giant impact. Note that core cooling rate and therefore MgO exsolution rate drop dramatically with the onset of inner core growth. The core at the present day is still exsolving MgO, albeit at a much slower rate than that prior to inner core growth.