Fig. 3.

(A) The evolution of FeO content in the magma ocean (MO) during Earth’s accretion. The color is coded according to redox states of the MO, with warmer colors corresponding to more oxidizing conditions. (B) Nb/Ta ratio in the BSE, and core–mantle partition coefficients of Nb (C) and Ta (D) at the end of Earth’s accretion, as a function of initial FeO content in the magma ocean. Each point in B–D corresponds to an output of the multistage core formation model with a linear evolution of fO₂ in A, except for the squares and triangles that follow the fO₂ paths proposed by refs. 7 and 10, dashed and dashed-dotted lines in A, respectively. The uncertainties are the intervals of y in the pressure range (40 to 70 GPa) of the MO allowed by the observables of Ni and Co partitioning (SI Appendix). The horizontal bars correspond to the targets, that is, present-day bulk D between core and mantle or subchondritic Nb/Ta ratio in the BSE. The observed subchondritic Nb/Ta ratio and Nb abundance in the BSE are matched with the initial FeO concentration from 2 to 18%.