238U/235U variations in meteorites: Extant 247Cm and implications for Pb-Pb dating

G. A. Brennecka, S. Weyer, Meenakshi Wadhwa, P. E. Janney, J. Zipfel, Ariel Anbar

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132 Scopus citations


The 238U/235U isotope ratio has long been considered invariant in meteoritic materials (equal to 137.88). This assumption is a cornerstone of the high-precision lead-lead dates that define the absolute age of the solar system. Calcium-aluminum-rich inclusions (CAls) of the Allende meteorite display variable 238U/235U ratios, ranging between 137.409 ± 0.039 and 137.885 ± 0.009. This range implies substantial uncertainties in the ages that were previously determined by lead-lead dating of CAls, which may be overestimated by several million years. The correlation of uranium isotope ratios with proxies for curium/uranium (that is, thorium/uranium and neodymium/uranium) provides strong evidence that the observed variations of 238U/235U in CAls were produced by the decay of extant curium-247 to uranium-235 in the early solar system, with an initial 247Cm/235U ratio of approximately 1.1 × 10-4 to 2.4 × 10-4.

Original languageEnglish (US)
Pages (from-to)449-451
Number of pages3
Issue number5964
StatePublished - Jan 22 2010

ASJC Scopus subject areas

  • General


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