Journal
SCIENCE
Volume 327, Issue 5964, Pages 449-451Publisher
AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/science.1180871
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Funding
- NASA Origins of Solar Systems [NNX07AF49G]
- NASA Astrobiology Institute [NNA09DA79A]
- NASA Exobiology Program [NNX07AU15G]
- NASA [119863, NNA09DA79A] Funding Source: Federal RePORTER
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The U-238/U-235 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 U-238/U-235 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 U-238/U-235 in CAIs were produced by the decay of extant curium-247 to uranium-235 in the early solar system, with an initial Cm-247/U-235 ratio of approximately 1.1 x 10(-4) to 2.4 x 10(-4).
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