This month, the Biden administration proclaimed Oct. 9 as “Leif Erikson Day” to celebrate Nordic Americans and the famed Viking leader and his crew, whom the White House called “bold explorers … believed to have been the first Europeans to reach the shores of North America,” centuries before Christopher Columbus.

In the 1960s, scientists uncovered an early Viking settlement in L’Anse aux Meadows in Newfoundland. Using carbon dating, researchers determined a rough period — 990 to 1050 — when Vikings were there.

But now scientists at the University of Groningen in the Netherlands have used a new kind of radiocarbon dating to determine an exact year when Vikings were in what is now Newfoundland: 1021, or one millennium ago.

In a study published Wednesday in the journal Nature, scientists analyzed radiocarbons embedded in the annual tree rings of three chunks of wood found at the Viking site.

Researchers already knew that the three wood samples came from three different trees. They also knew that Indigenous people could not have cut the slabs, as the wood showed signs of a metal blade, which Vikings, and not local communities, possessed at the time. The ancient outpost was similar to Viking settlements found across the western coast of Norway, Iceland and Greenland, said Raymond Sauvage, a professor in the department of archaeology and cultural history at the Norwegian University of Science and Technology.

Moreover, scientists knew that a solar storm around 993 would have shot high-energy cosmic rays into the atmosphere — and that a higher-than-usual concentration of radiocarbons became embedded in every tree alive at the time.

So they analyzed the annual growth rings found in the chunks of wood at the Viking site. Sure enough, the three samples showed evidence of being around when the solar storm of 993 raged. The subsequent number of annual rings on each tree told researchers that the trees had been cut down in 1021, according to the study.

“Much kudos should go to these Northern Europeans for being the first human society to traverse the Atlantic,” geoscientist Michael Dee of the University of Groningen in the Netherlands, who co-led the study, told Reuters.

Much, however, remains a mystery about North America’s earliest known Viking settlement. Scientists have not found evidence that it was in use past 1050, but they do not know exactly when it began.

“It was likely an outpost from their Greenland settlement,” said Sauvage, who estimated it was in use for only a short while.

Vikings probably came in search of resources: wood for buildings and boats, iron for tools, and other materials needed to fix their boats, all of which would have been in ample supply at L’Anse aux Meadows.

Still, the study is “very exciting” on several scientific and historical levels, said Sauvage.

“Radiocarbon dating as a method for archaeology is becoming more and more important,” he said.

But knowing more about when the Vikings roamed also challenges some misconceptions about how communities in the past engaged, Sauvage said.

“People in historical periods were more mobile than we normally think,” he said. “Northern Europeans were able to travel across the Atlantic 1,000 years ago. And they met Indigenous populations there, also.”

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