A catastrophe described nearly 2,000 years ago has now served as a measuring stick to improve a dating method.
The eruption of Vesuvius that buried Pompeii in AD 79 offers a rare advantage for geologists: historical accounts make it possible to determine its period with great precision. Researchers used this reference point to verify and recalibrate a dating method applied to volcanic rocks. Their result brings the timescales of historians and geologists closer together.
Depiction of Vesuvius erupting in AD 79
Jean-Baptiste François Génillon · Public domain
The method is called argon-argon dating. Some rocks contain potassium, a small part of which naturally transforms into argon over time. By measuring different types of argon in a mineral, scientists can calculate how long ago it formed.
The team analyzed eight samples of sanidine, a potassium-rich mineral found in pumice stones from Vesuvius. These materials came from the beginning of the eruption, making them particularly well suited to the experiment. Traditional measurements produced an age of 1,938 years, with a margin of 13 years in either direction, based on analyses carried out in 2025.
The historical reference point corresponds to an eruption that occurred 1,946 years before these measurements. The difference between the two values therefore remains small. But it is not insignificant, and it makes it possible to recalibrate the dating method and its uncertainty.
An old question must also be examined: did Pliny the Younger give the correct date? The traditionally accepted date is August 24, AD 79, but some archaeological clues had supported the hypothesis of a later eruption. In particular, the team reexamined a coin found in Pompeii and believes that it may have been minted before September.
The researchers ultimately retained a historical uncertainty of two months. This margin has little effect on the calibration of rock dating.
The team now wants to bring several major dating methods closer together. Argon-argon dating could in particular serve as a reference for checking radiocarbon dating, used on relatively recent organic materials, or the uranium-lead method applied to much older rocks.