An event with cosmic rays determines the landing of the Vikings in Canada

The sites Dee and colleagues explored, restored by L’Anse aux Meadows decades ago and carefully preserved in a freezer at a Parks Canada warehouse in Dartmouth, Nova Scotia, fit the bill perfectly. These include a stump that may have been removed from the ground while the ground around the Viking site was being cleared – and which, critically, still had an intact “bark edge.” Since there were 28 rings from the ring with carbon spikes to the edge, the felling of the tree can be associated with 1021 AD. (The fact that this is exactly 1,000 years ago is a coincidence, albeit a welcome one, Dee says.)

The team of Dutch, German and Canadian scientists, led by Dee and his Groningen colleague Margo Quitems, published their study in nature on October 20th. One of their co-authors is Birgita Wallace, a Canadian archaeologist who has been working on the site since the 1960s. Dee attributes to Wallace, who is now in her late seventies, that she had the mind to keep the pieces of wood used in the present study. “A lot of people would just throw it away. But she decided that science could one day benefit from them and put them in the freezer to keep them well-preserved for 40 years, ”he said.

“It’s a really good paper – it dates this tree very accurately,” said Timothy Jules, a radiocarbon dating expert at the University of Arizona who was not involved in the current study. Previously, studies using dendrochronology– The science of determining the age of a tree from the relative growth rates recorded in its rings – requires cross-comparisons involving a large number of trees in order to calibrate a new sample and make a (often quite rough) estimate of its age. “But in this case, they didn’t have to do that because they have this spike that tells them exactly where they are [in the timeline]. That’s what makes it such a good study, “says Jules.

Scientists have long believed that high-energy particles produced by solar activity and other astrophysical sources such as supernovae arrive on Earth in a more or less constant stream. This would mean that the ratio of carbon-14 to its stable cousins ​​would be relatively constant over time. But in 2012, Japanese physicist Fusa Miyake discovered trees containing a carbon-14 peak, dating from 774 to 775 AD. Scientists now believe that there have been a handful of these high-energy particle bursts in the last 10,000 years.

Because these events are so rare, researchers like Dee and his colleagues can be sure that they are not just looking at some random peak of carbon-14, but specific – which means they can be sure of the date they attach to it. Other spikes, meanwhile, can be used to identify other historical events. (The same technique was used recently to determine the date when a medieval church was built in Switzerland, from a study of its roof beams.)

Remains of a Viking structure at the L’Anse aux Meadows National Historic Site in Newfoundland.

Photo: Dan Falk

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