Abstract The thermal conductivity of the Earth’s core is crucial for assessing the thermal evolution and thermal state of the core. Previous experimental and computational studies have produced widely varying estimates of the core’s thermal conductivity. Silicon is likely a significant light element in the Earth’s iron‐rich core. Here, we utilized the machine learning method to compute the lattice thermal conductivity of hcp Fe‐Si alloys at room temperature and high pressure. The lattice thermal conductivity of Fe‐Si alloys is significant at room temperature, but it becomes small (3%) and negligible under Earth’s core conditions. The comparison between calculations and experimental data at room temperature provides insights into the discrepancies in previous studies. We calculated the total thermal conductivity of solid hcp Fe‐8.7wt%Si alloy to be at least 90 W/m/K at the Earth’s core‐mantle boundary, implying a relatively young inner core if Si were the major light element in the core.

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