Argon Dating Pins the Pompeii Eruption to Within 13 Years

Writing in Science Advances on Sept. 25, a team led by Paul R. Renne of the Berkeley Geochronology Center dated the Vesuvius eruption that Pliny the Younger witnessed in 79 CE to 1,938 ± 13 years before the measurement, which was made in 2025. Renne and colleagues report 0.7% precision and 0.4% accuracy at that age, and describe the result as a precedent for the argon-40/argon-39 method, a radioactive-decay clock.

The paper reports that the same data also fixed the rate at which potassium-40 decays into argon-40, twice as precisely as disintegration counting, which counts decay events directly. The authors say the sharper value improves the accuracy of argon dating throughout geologic time, and makes the method more applicable to tracking how magma systems evolve, including volcanic hazard assessment.

The team credits the precision at so young an age to improvements in mass spectrometry, a different strategy for irradiating the samples with neutrons, and a measurement of the interfering isotopes that the irradiation itself creates.

The year 79 CE comes from the historical record rather than from geology, which is what lets a laboratory age be compared with a date already known. The authors also offer their result as a reference point for calibrating the method against other ways of dating rock.

Andrea Marzoli of the University of Padua in Italy is the paper's senior author, and the remaining authors are at the Berkeley Geochronology Center and the University of California, Berkeley. The National Science Foundation and the Ann and Gordon Getty Foundation funded the work, according to the record published with the paper.