Pompeii eruption and Pliny's eyewitness account sharpen a key geological dating clock
The eruption of Mount Vesuvius that buried Pompeii in 79 CE has given geologists a better way to date events deep in Earth's past. In a study published in Science Advances on September 25, 2026, researchers from the Berkeley Geochronology Center, UC Berkeley and the University of Padua used the eruption's known date, recorded by the Roman writer Pliny the Younger, to test and calibrate argon-argon dating, one of the main methods for dating volcanic rocks.
Testing the clock against history
Argon-argon dating relies on the natural decay of potassium-40 into argon-40. According to UC Berkeley, scientists irradiate a rock sample with neutrons to convert potassium-39 into argon-39 and then compare the ratios of argon isotopes.
The team analyzed eight samples of sanidine, a potassium-bearing volcanic mineral, taken from pumice at Oplontis, another Roman town buried in the eruption. The samples came from ash deposits laid down in the eruption's earliest stage.
The measurements placed the eruption 1,938 years, plus or minus 13 years, before the minerals were analyzed in 2025. The minerals' true age, based on the historical record, was 1,946 years. UC Berkeley reports a precision of 0.7 percent and an accuracy of 0.4 percent.
"We wanted to see how precisely and accurately we could date something that's very recent," study leader Paul Renne, director of the Berkeley Geochronology Center and a UC Berkeley professor, told Gizmodo. He described the result as accurate "to within a decade, which is pretty good."
A better half-life
Pliny the Younger, whose uncle Pliny the Elder died in the eruption, left a first-hand account of the event. Graduate student Caroline Hasler examined the historical records and validated the August 24 date to within two months, according to UC Berkeley.
With that anchor, the team refined the half-life of potassium-40 to 12.044 billion years, plus or minus 0.088 billion years. UC Berkeley says this is twice as precise as the earlier value derived from nuclear physics.
"If you want to put together the eruptive history of a volcano in relatively recent time, precision and accuracy really count," Renne said. "The study shows that you can achieve that kind of highly useful precision and accuracy into the historical realm."
From Pompeii to the dinosaurs
Renne has previously used argon-argon dating to establish ages for a meteor impact, major volcanic eruptions in India and the extinction of the dinosaurs, all about 66 million years ago. A more precise half-life helps with questions like these. "This lets us more precisely infer causality between events in the geologic record, for example a meteor impact structure and a mass extinction," Renne said.
He added that the team hopes to bring other dating techniques into line with the same approach. "It's nice to have all of your different clocks giving you the same answer," he told Gizmodo.
Why it matters
Radiometric dating underpins the timeline of Earth's history, from volcanic eruptions to mass extinctions. Checking a method against an event with a precisely known date is rare, and the Vesuvius eruption offers one of the best such tests. A more precise potassium-40 half-life should tighten ages across a wide range of geological events, including those around the end of the dinosaurs.
Sources
- UC Berkeley News, "The eruption that destroyed Pompeii is helping scientists date Earth's history"
- Gizmodo, "Scientists Dated the Catastrophic Pompeii Eruption Using Only Rocks. Here's How Close They Got"
- ScienceDaily, "Pompeii's 2,000-year-old eruption just gave scientists a better clock for Earth's past"
This article was drafted with AI assistance and checked against the sources above. Company claims are reported as claims. Cover image is AI-generated.
