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Dr. “It’s handled by photosynthesis,” Dee said.

The vast majority of carbon in the atmosphere is carbon 12, a stable atom with six protons and six neutrons. Only a fleeting fraction is radioactive carbon 14, also called radiocarbon. This isotope of carbon is produced when cosmic rays – high-energy particles from the sun or beyond the solar system – interact with atoms in Earth’s atmosphere.

Scientists studying cosmic rays used to think that these particles came with a relatively constant barrage, meaning that the ratio of carbon 14 to carbon 12 in the atmosphere remains largely constant over time. But then in 2012 researchers found two cedar trees in Japan. inexplicably high levels of radiocarbon In its rings from 774 to 775 AD. Other Miyake events have since been spotted in tree ring records, but they remain extremely rare.

Dr. “Right now there are only three or four in all of the last 10,000 years,” Dee said.

But it so happened another Miyake event It occurred during the Viking Age, 992-993 AD. Trees found worldwide recorded an increase in carbon 14 over that time, and the wood found at L’Anse aux Meadows should be no exception. Hoping to determine the age of the Americas’ only confirmed Viking settlement, Dr. Dee and colleagues turned to the unlikely marriage of dendrochronology — the study of tree rings — and astrophysics.

Dr. “We realized that this could change the game,” Dee said.

The researchers found that all three pieces of wood exhibited a marked increase in radiocarbon starting 28 ringing before their outer bark. The team concluded that ring 28 must correspond to the year 993 AD. They ruled out earlier and later Miyake events based on carbon 14 to carbon 12 ratios measured in wood and varying in known ways over the centuries.

Dr. “All you have to do is count the time you’ve reached the cutting edge,” said Dee, with a date now pinned to an inner tree ring. The researchers calculated that the three pieces of wood the team analyzed were cut in 1021.

So far, estimates of when L’Anse aux Meadows was occupied have been largely “guessed,” said Sturt Manning, an archaeologist at Cornell University and director of the Cornell Tree-Ring Laboratory, who was not involved in the research. “Here’s conclusive, tangible evidence linked to a year.”