Synchronizing rock clocks of Earth history

Calibration of the geological time scale is achieved by independent radioisotopic and astronomical dating, but these techniques yield discrepancies of similar to 1.0% or more, limiting our ability to reconstruct Earth history. To overcome this fundamental setback, we compared astronomical and 40Ar/39Ar ages of tephras in marine deposits in Morocco to calibrate the age of Fish Canyon sanidine, the most widely used standard in 40Ar/39Ar geochronology. This calibration results in a more precise older age of 28.201 +/- 0.046 million years ago ( Ma) and reduces the 40Ar/39Ar method's absolute uncertainty from similar to 2.5 to 0.25%. In addition, this calibration provides tight constraints for the astronomical tuning of pre- Neogene successions, resulting in a mutually consistent age of similar to 65.95 Ma for the Cretaceous/ Tertiary boundary.