A new study has made argon-argon dating more precise by using the well-recorded eruption of Mount Vesuvius in 79 CE.
Sunset Over Ancient Ruins of Pompeii, Italy. Credit: Nirjhar Basak
The eruption buried Pompeii and killed Pliny the Elder. His nephew, Pliny the Younger, witnessed the event and recorded a detailed account. Researchers used his record as a fixed date for testing and improving a major method for dating volcanic rocks.
Scientists from the Berkeley Geochronology Center, UC Berkeley, and the University of Padua tested volcanic minerals from Vesuvius. Their results place the eruption at 1,938 ± 13 years before measurement in 2025.
The result gives argon-argon dating a precision of 0.7% and an accuracy of 0.4%. Such precision is rare for an eruption as young as Vesuvius. The work also sets a new benchmark for dating recent volcanic events.
Argon-argon dating tracks the decay of potassium-40 into argon-40. Volcanic minerals hold little argon before an eruption. Once magma cools into rock, argon from radioactive decay starts building up inside the mineral.
Researchers measure argon isotopes in a sample to estimate its age. Neutron irradiation also turns potassium-39 into argon-39. Comparing argon-39 and argon-40 then provides the basis for the age calculation.
Aerial image of Pompeii and Mount Vesuvius. Credit: Carsten Steger, CC BY-SA 4.0
The team tested eight samples of sanidine, a potassium-rich volcanic mineral. The samples came from pumice deposits at Oplontis, a Roman settlement buried during the Vesuvius eruption.
The Oplontis samples had an important advantage. They came from the earliest stage of the eruption and contained more potassium than earlier samples.
Andrea Marzoli of the University of Padua collected the samples in 1998. They then stayed unused for decades. Researchers later returned to them while seeking better results than an earlier 1997 study.
Several advances helped the new work. The team used better samples, improved mass spectrometry, and a new neutron irradiation strategy. Researchers also improved their treatment of neutron-produced isotopes.
These changes helped the team reach precision below 1%. The new results also produced a more precise value for the half-life of potassium-40.
Researchers calculated a half-life of 12.044 billion years, with an uncertainty of 0.088 billion years. The figure is twice as precise as the earlier value from nuclear physics measurements.
The historical date of the eruption also needed careful review. Pliny’s account supports August 24, 79 CE, but some historians have argued for a later date.
Cone of the Vesuvius. Credit: The Dronaut, CC BY-SA 4.0
Graduate student Caroline Hasler examined the historical record, including a coin found at Pompeii. Some researchers linked the coin to a September date. Her comparison with other Roman coins suggested production before September.
The team allowed a two-month uncertainty around the historical date. The uncertainty had little effect on calibration of the dating method. The wider date range helped establish the potassium-40 half-life with greater confidence.
The improved method has uses far beyond Vesuvius. More precise dates help researchers compare volcanic eruptions with other events recorded in geological layers.
The method also helps test other dating systems. These include radiocarbon dating for younger organic material and uranium-lead dating for ancient rocks.
Better dates also matter when studying volcanoes near large cities. Examples include volcanic systems near Mexico City, Naples, and Yogyakarta in Indonesia. Past eruption records help researchers study how those systems changed over time.
The new results also support efforts to bring different geological dating methods into closer agreement. Researchers have used Bayesian methods to compare argon-argon and uranium-lead dates.
The stronger Vesuvius result now provides a more precise historical reference for such work. The study also gives argon-argon dating a stronger basis for measuring recent eruptions.
A 2,000-year-old Roman disaster has therefore become a useful test for one of geology’s key dating tools. The Vesuvius eruption now provides a precise benchmark for measuring volcanic events through geologic time.
Publication: Renne, P. R., Cassata, W. S., Hasler, C. E. J., Carter, J. N., Fuentes, A. J., Tholt, A. J., & Marzoli, A. (2026). Pliny the Younger advances geochronology. Science Advances, 12(39). doi:10.1126/sciadv.aeg262