Evaluation of the 129 I Half-Life Value Through Analyses of Primitive Meteorites.

The preserved record of decay of now-extinct 129 I into 129 Xe forms the basis of the I-Xe chronometer. Comparison of the high precision I-Xe and Pb-Pb ages of chondrules and pure mineral phases separated from eight meteorites suggests the 17.5 ÷ 14.6 Ma range for the 129 I half-life, assuming that the 235 U and 238 U half-lives are correct. The mean value of 16 Ma indicates that the 15.7 Ma half-life of 129 I used here for the I-Xe age calculations is most probably correct. Since the 129 I half-life value only affects the relative I-Xe ages, the few Ma relative to the Shallowater standard, the absolute I-Xe ages are almost immune to this uncertainty in the 129 I half-life.