Extended Data Fig. 4. Carbon and nitrogen contents in the alloy melts as a function of oxygen fugacity.

a) C content in the alloy melt in graphite-undersaturated experiments of this study is substantially lower (0.11-0.80 wt.%) than the graphite-saturated experiments of the previous studies^{10–13,25,29}. b) In agreement with previous studies in graphite-saturated conditions, N content in the alloy melt decreases with decrease in fO₂ in graphite-undersaturated conditions. However, at any given fO₂, N in graphite-undersaturated alloys is substantially greater than graphite-saturated alloys. $D_{\text{N}}^{\text{alloy/silicate}}$ for graphite-saturated alloys has been determined only in N-undersaturated conditions, therefore, N content in the alloys from only two previous studies^10,11 was compared with the data from the present study because of similar N contents in the starting mixtures. Error bars represent ±1-σ deviation based on the replicate electron microprobe analyses; where absent, the error bars are smaller than the symbol size.