  The extinct p-process nuclide 146Sm serves as an astrophysical and
geochemical chronometer through measurements of isotopic anomalies of its
alpha-decay daughter 142Nd. Based on analyses of 146Sm/147Sm alpha-activity and
atom ratios, we determined the half-life of 146Sm to be 68 \pm 7 (1sigma)
million years (Ma), which is shorter than the currently used value of 103 \pm 5
Ma. This half-life value implies a higher initial 146Sm abundance in the early
solar system, (146Sm/144Sm_0 = 0.0094\pm0.0005 (2sigma), than previously
estimated. Terrestrial, Lunar and Martian planetary silicate mantle
differentiation events dated with 146Sm-142Nd converge to a shorter time span
and in general to earlier times, due to the combined effect of the new 146Sm
half-life and (146Sm/144Sm)_0 values.
