Melting and resistivity of iron at Earth core conditions using pulsed Joule heating

The melting temperature and electrical resistivity of iron at high pressure are essential for understanding Earth’s core. Here we use a new high-pressure method – microsecond pulsed Joule heating in diamond anvil cells – to identify melting and measure resistivity of solid and liquid iron. More than 300 reproducible melting measurements indicate a surprisingly shallow melting curve, reaching 6 K/GPa and 4160 ± 80 K at 200 GPa. Extrapolating in pressure and iron alloy composition, and combining with our 76 μ Ω cm measurement of liquid iron’s resistivity, we infer a relatively cold core-mantle boundary (3430 K) with a low adiabatic outer core heat flow (9.8 TW). This suggests thermal convection alone could have powered the geodynamo prior to inner core formation and that today’s lowermost mantle is fully solid.