D and his colleagues perfectly fit items recovered from L’Anse aux Meadows decades ago and carefully stored items in a freezer at a Park Canada storage facility in Dartmouth, Nova Scotia. It contains a tree stump that may have been pulled from the ground as the land around the Viking site is being cleared – and which critically still has its “bark edge” intact. Since there were 28 rings at the ends from the carbon-spike ring, the tree cut can be estimated up to 1021 AD. )
A team of Dutch, German and Canadian scientists, led by D and his Groningen colleague Margot Quetimes, conducted their study. Nature October 20. One of their colleagues is Canadian archaeologist Birgitta Wallace, who has worked on the site since the 1960s. D credits Wallace, who is now in his late seventies, for his presence of mind to preserve the pieces of wood used in the present study. “A lot of people would remove it. But he thought science might one day use them, and refrigerate them so that they would be well-preserved for 40 years, ”he said.
“It’s a really nice piece of paper – it says this wood very precisely,” said Timothy Jules, a radiocarbon dating expert at the University of Arizona. Previously, studies using dendrochronology-the relative growth rate of a tree to determine its age in its rings-required cross-comparison of a large number of trees to calibrate a new specimen and to bring in one (often quite rough). Guess his age. “But in this case, they didn’t have to do it, because they have this spike that tells them exactly where they are [in the timeline]. That’s what makes it such a beautiful study, ”says Jules.
Scientists have long believed that highly energetic particles produced by solar activity and other astronomical sources such as supernovae come to Earth in a more or less steady flow. This means that the ratio of stable cousins to carbon-14 will be fairly constant over time. But in 2012, Japanese physicist Fusa Mia found a carbon-1 sp spike tree from AD to 755 AD. Scientists now believe that these few high-energy particles have exploded in the last 10,000 years.
Since these events are very rare, researchers like D and his colleagues can be confident that they are not only seeing some random carbon-14 spikes, but a specific event যার which means they can be confident about the date attached to it. Meanwhile, other spikes can be used to identify other historical events. (The same technique was recently used to mark the date of the construction of a medieval church in Switzerland, from a study of its roof beams.)