Extended Data Fig. 5. $D_{\text{N}}^{\text{alloy/silicate}}$ as a function of oxygen fugacity and (a) silicon content in the alloy and (b) temperature.

a) In addition to the effect of fO₂, when Si content in the alloy melt and FeO content in the silicate melt are coupled to each other, incorporation of Si into the alloy melt on its own has a strong negative effect on N content in the alloy at a similar logfO₂ (~IW–4; here shown by grey rectangle). A similar effect has been observed in a previous study¹¹ albeit at a higher logfO₂ (~IW–2.5) because in graphite-saturated alloys, Si expels N from the alloy melt even at lower concentrations (as low as 0.1 wt.% Si). b) In contrast to the observations of previous studies^11,12 in graphite-saturated conditions, temperature does not have any discernible effect on $D_{\text{N}}^{\text{alloy/silicate}}$ in the limited temperature range explored in this study. Error bars represent ±1-σ deviation obtained by propagation of ±1-σ deviation on N content in the alloy and silicate melts; where absent, the error bars are smaller than the symbol size.