Geochemistry: How well can Pb isotopes date core formation?

Arising from: B. J. Wood & A. N. Halliday 437, 1345-1348 (2005); Wood & Halliday reply. Timescale and the physics of planetary core formation are essential constraints for models of Earth's accretion and early differentiation. Wood and Halliday use the apparent mismatch in core-formation dates determined from tungsten (W) and lead (Pb) chrono-meters to argue for a two-stage core formation, involving an early phase of metal segregation followed by a protracted episode of sulphide melt addition. However, we show here that crust-mantle Pb isotope systematics do not require diachronous core formation. Our observations indicate that very early (≥ 35 Myr) core formation and planet accretion remain the most plausible scenario.