Long- and short-lived radioactive isotopes and their daughter products in meteorites are chronometers that can test models for Solar System formation^{1, 2}. Differentiated meteorites come from parent bodies that were once molten and separated into metal cores and silicate mantles. Mineral ages for these meteorites, however, are typically younger than age constraints for planetesimal differentiation^{3, 4, 5}. Such young ages indicate that the energy required to melt their parent bodies could not have come from the most likely heat source⁶—radioactive decay of short-lived nuclides (²⁶Al and ⁶⁰Fe) injected from a nearby supernova—because these would have largely decayed by the time of melting. Here we report an age of 4.5662 0.0001 billion years (based on Pb–Pb dating) for basaltic angrites, which is only 1 Myr younger than the currently accepted minimum age of the Solar System⁷ and corresponds to a time when ²⁶Al and ⁶⁰Fe decay could have triggered planetesimal melting. Small ²⁶Mg excesses in bulk angrite samples confirm that ²⁶Al decay contributed to the melting of their parent body. These results indicate that the accretion of differentiated planetesimals pre-dated that of undifferentiated planetesimals, and reveals the minimum Solar System age to be 4.5695 0.0002 billion years.

1. School of Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand
2. Geological Institute, Øster Voldgade 10, DK-1350, Denmark
3. Geological Museum, Øster Voldgade 5–7, DK-1350, Denmark
4. Department of Geological Sciences, The University of Texas at Austin, 1 University Station C1100, Austin, Texas 78712-02, USA

Correspondence to: Joel Baker¹ Correspondence and requests for materials should be addressed to J.B. (Email: joel.baker@vuw.ac.nz).

Received 21 December 2004; Accepted 1 June 2005

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