The extinct p-process nuclide Sm-146 serves as an astrophysical and geochemical chronometer through measurements of isotopic anomalies of its alpha-decay daughter Nd-142. Based on analyses of Sm-146/Sm-147 alpha-activity and atom ratios, we determined the half-life of Sm-146 to be 68 +/- 7 (1 sigma) million years, which is shorter than the currently used value of 103 +/- 5 million years. This half-life value implies a higher initial Sm-146 abundance in the early solar system, (Sm-146/Sm-144)(0) = 0.0094 +/- 0.0005 (2 sigma), than previously estimated. Terrestrial, lunar, and martian planetary silicate mantle differentiation events dated with Sm-146-Nd-142 converge to a shorter time span and in general to earlier times, due to the combined effect of the new Sm-146 half-life and (Sm-146/Sm-144)(0) values.