“It’s taken with photosynthesis,” Dr. Dee said.
The vast majority of carbon in the atmosphere is carbon 12, a stable atom with six protons and six neutrons. Only an ephemeral 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 the Earth’s atmosphere.
Scientists studying cosmic rays believed that these particles land in a relatively constant dam, which means that the ratio of carbon-14 to carbon-12 in the atmosphere has remained largely stable over time. But in 2012, researchers found two cedars in Japan that recorded inexplicably high levels of radiocarbon in their rings dating from AD 774 to AD 775. This peak is now known as a Miyake event to its discoverer, Fusa Miyake, a cosmic ray physicist in Nagoya. University in Japan. Other Miyake events have since been spotted in tree ring records, but they remain extremely rare.
“Right now we only have three or four in the last 10,000 years,” said Dr Dee.
But it turns out that another Miyake event happened during the Viking Age, between 992 and 993. Trees found around the world recorded an increase in carbon-14 at this time, and wood found at L’Anse aux Meadows should be no exception. Hoping to determine the age of the only confirmed Viking settlement in the Americas, Dr Dee and his colleagues turned to the unlikely marriage of dendrochronology – the study of tree rings – and astrophysics.
“We realized this could be a game-changer,” Dr Dee said.
The researchers found that their three pieces of wood all exhibited a pronounced increase in radiocarbon that started 28 rings before their outer bark. Ring 28 must correspond to the year 993 AD, the team concludes. They excluded earlier and later Miyake events based on the carbon 14 to carbon 12 ratios measured in wood, which vary in known ways over the centuries.
With a date now pinned to an inner shaft ring, “all you have to do is count until you hit the tip,” Dr. Dee said. The three pieces of wood the team analyzed were all felled in 1021, the researchers calculated.
Until now, estimates of the occupation of L’Anse aux Meadows were largely “estimates,” said Sturt Manning, an archaeologist at Cornell University and director of the Cornell Tree Ring Laboratory, which was not. involved in research. “Here is concrete and concrete evidence that relates to one year. “