science
A teenager's letter from 79 CE sharpened Earth's rock clock
A dying man's nephew wrote it all down. The clock still runs.
A letter written nearly 2,000 years ago has helped scientists build a sharper clock for Earth's deep past. When Mt. Vesuvius erupted in 79 CE, Pliny the Younger recorded enough detail to pin the disaster to Aug. 24, which gave modern researchers a rare fixed point in recorded history to test a dating method against. Writing in Science Advances, a team led by Paul Renne of the Berkeley Geochronology Center used that date to refine argon-argon dating, the tool geologists rely on to age rocks and eruptions. They measured eight samples of a volcanic mineral from Vesuvius and landed within eight years of the known age, a precision of 0.7 percent. The best material came from pumice collected at Oplontis in 1998, then left in storage for decades until graduate students proposed digging it back out. "Precision and accuracy really count," Renne said. The method can now date eruptions within living memory to the decade.
