Does U–Pb date Earth's core formation?

Abstract

Arising from: B. J. Wood & A. N. Halliday Nature 437, 1345–1348 (2005); Wood & Halliday replyConstraining the timing of the formation of Earth's core, which defines the birth of our planet, is essential for understanding the early evolution of Earth-like planets. Wood and Halliday1 and Halliday2 discuss the apparent discrepancy between the U–Pb (60–80 Myr) and Hf–W clocks (30 Myr) in determining the timescale of Earth's accretion and core formation. We find that the information the authors present is at times contradictory (for example, compare Fig. 1 in ref. 1 with Fig. 1 in ref. 2) and confusing and could suggest that the U–Pb clock constrains core formation better than the Hf–W system. Here we point out the limitations of the U–Pb system and show that the U–Pb age cannot be used to argue for protracted accretion and/or core formation (>50 Myr) because this clock only records the processes that occurred during the last 1% of Earth's accretion and core formation in the Wood and Halliday mechanism1.