title: 238U/235U variations in meteorites: extant 247Cm and implications for Pb-Pb dating.
abstract: 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 (CAIs) 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 CAIs, 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 CAIs 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 x 10(-4) to 2.4 x 10(-4).
authors.affiliation: School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA. brennecka@asu.edu
authors.forename: G A
authors.initials: GA
authors.lastname: Brennecka
authors.forename: S
authors.initials: S
authors.lastname: Weyer
authors.forename: M
authors.initials: M
authors.lastname: Wadhwa
authors.forename: P E
authors.initials: PE
authors.lastname: Janney
authors.forename: J
authors.initials: J
authors.lastname: Zipfel
authors.forename: A D
authors.initials: AD
authors.lastname: Anbar