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Published on: May 20, 2019
238U/235U variations in meteorites: extant 247Cm and implications for Pb-Pb dating.
G A Brennecka1, S Weyer, M Wadhwa
1School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA. brennecka@asu.edu
Science (New York, N.Y.)
|January 2, 2010
Summary
The uranium isotope ratio in meteorites is not constant, challenging the accuracy of solar system age calculations. Variations in Calcium-Aluminum-rich inclusions suggest dating methods may overestimate ages by millions of years.
Area of Science:
- Cosmochemistry
- Geochronology
- Nuclear Astrophysics
Background:
- The uranium-238/uranium-235 (238U/235U) isotope ratio is assumed constant in meteorites.
- This assumption underpins high-precision lead-lead dating for determining the solar system's age.
Purpose of the Study:
- To investigate the variability of the 238U/235U isotope ratio in meteoritic materials.
- To reassess the implications of these variations for solar system chronology.
Main Methods:
- Analysis of Calcium-Aluminum-rich inclusions (CAIs) from the Allende meteorite.
- Measurement of 238U/235U isotope ratios.
- Correlation of uranium isotope variations with proxies for curium/uranium (Th/U, Nd/U).
Main Results:
- Observed variable 238U/235U ratios in CAIs, ranging from 137.409 to 137.885.
- Identified potential overestimation of CAI ages by several million years due to dating uncertainties.
- Strong evidence linking 238U/235U variations to the decay of curium-247 (247Cm) to uranium-235 (235U).
Conclusions:
- The initial 247Cm/235U ratio in the early solar system was approximately 1.1 x 10(-4) to 2.4 x 10(-4).
- The decay of 247Cm is a significant factor influencing 238U/235U ratios in early solar system materials.
- Reevaluation of lead-lead dating of CAIs is necessary.
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