Low thermal conductivity of iron-silicon alloys at Earth's core conditions with implications for the geodynamo

Earth's core is composed of iron (Fe) alloyed with light elements, e.g., silicon (Si). Its thermal conductivity critically affects Earth's thermal structure, evolution, and dynamics, as it controls the magnitude of thermal and compositional sources required to sustain a geodynamo over Earth's history. Here we directly measured thermal conductivities of solid Fe and Fe-Si alloys up to 144GPa and 3300K. 15 at% Si alloyed in Fe substantially reduces its conductivity by about 2 folds at 132GPa and 3000K. An outer core with 15 at% Si would have a conductivity of about 20Wm(-1) K-1, lower than pure Fe at similar pressure-temperature conditions. This suggests a lower minimum heat flow, around 3 TW, across the core-mantle boundary than previously expected, and thus less thermal energy needed to operate the geodynamo. Our results provide key constraints on inner core age that could be older than two billion-years. Thermal conductivity of Earth's core affects Earth's thermal structure, evolution and dynamics. Based on thermal conductivity measurements of iron-silicon alloys at high pressure and temperature conditions, the authors here propose Earth's inner core could be older than previously expected.