40 Ar/ 39 Ar Dating into the Historical Realm: Calibration Against Pliny the Younger

Abstract
Laser incremental heating of sanidine from the pumice deposited by the Plinian eruption of Vesuvius in 79 A.D. yielded a 40 Ar/ 39 Ar isochron age of 1925 ± 94 years ago. Close agreement with the Gregorian calendar–based age of 1918 years ago demonstrates that the 40 Ar/ 39 Ar method can be reliably extended into the temporal range of recorded history. Excess 40 Ar is present in the sanidine in concentrations that would cause significant errors if ignored in dating Holocene samples.