Extended Data Fig. 1. Comparison of the silicate melt compositions of this study with previous studies as a function of oxygen fugacity.

Below IW–1.5 (fO₂ range explored in this study), the silicate melt compositions of this study are more mafic, i.e., have higher NBO/Ts, relative to the silicate melt compositions used to determine $D_{\text{N}}^{\text{alloy/silicate}}$ in previous studies. Therefore, the silicate melt compositions of this study are more representative of magma oceans of inner Solar System rocky planets. Primitive mantle compositions are used to estimate the magma ocean compositions of Earth⁶⁰, Mars⁶¹ and Mercury⁶². NBO/T is a measure of degree of silicate melt polymerization and is expressed as total non-bridging oxygens per tetrahedral cations; NBO/T = (2 × Total O)/T – 4, where T = Si + Ti + Al + Cr + P). The calculated error bars for NBO/T represent ±1-σ deviation based on the replicate electron microprobe analyses and are smaller than the symbol sizes for all data from this study.