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Early planetesimal melting from an age of 4.5662 Gyr for differentiated meteorites


Long- and short-lived radioactive isotopes and their daughter products in meteorites are chronometers that can test models for Solar System formation1,2. 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 differentiation3,4,5. 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.

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Figure 1: Pb–Pb age and isotope data for angrites.
Figure 2: Timing of angrite magmatism and parent body (APB) accretion compared with upper age limits for accretion of chondrite parent bodies.


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Financial support for this project was provided by the Danish Lithosphere Centre (funded by the Danish National Science Foundation). L. Labenne is thanked for his efforts in finding SAH99555 and providing our angrite samples. C. Stirling provided us with a pre-print of her U isotope study of meteorites. NASA supplied the Martian meteorite EETA79001. V. Fernandes provided us with lunar meteorite NWA032. Y. Amelin is thanked for his feedback on an earlier version of this paper.

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Correspondence to Joel Baker.

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Supplementary Methods

Description of analytical methods for Pb and Mg isotopic analysis. (DOC 32 kb)

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Baker, J., Bizzarro, M., Wittig, N. et al. Early planetesimal melting from an age of 4.5662 Gyr for differentiated meteorites. Nature 436, 1127–1131 (2005).

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