Rapid accretion and early core formation on asteroids and the terrestrial planets from Hf-W chronometry

The timescales and mechanisms for the formation and chemical differentiation of the planets can be quantified using the radioactive decay of short-lived isotopes(1-10). Of these, the Hf-182-to-W-182 decay is ideally suited for dating core formation in planetary bodies(1-5). In an earlier study, the W isotope composition(1) of the Earth's mantle was used to infer that core formation was late(1) (greater than or equal to60 million years after the beginning of the Solar System) and that accretion was a protracted process(11,12). The correct interpretation of Hf-W data depends, however, on accurate knowledge of the initial abundance of Hf-182 in the Solar System and the Wisotope composition of chondritic meteorites. Here we report Hf-W data for carbonaceous and H chondrite meteorites that lead to timescales of accretion and core formation significantly different from those calculated previously(1,3,5,11,12). The revised ages for Vesta, Mars and Earth indicate rapid accretion, and show that the timescale for core formation decreases with decreasing size of the planet. We conclude that core formation in the terrestrial planets and the formation of the Moon must have occurred during the first similar to30 million years of the life of the Solar System.