Ancient solar storm pinpoints Viking settlement in Americas exactly 1,000 years ago

In A.D. 993, a storm on the sun released an enormous pulse of radiation that was absorbed and stored by trees all over the Earth. Now, that solar event has proved a critical tool in pinpointing an exact year the Vikings were present in the Americas.

Since the discovery of a Viking settlement at L’Anse aux Meadows in Canada's Newfoundland more than 50 years ago, most scholars accept that Viking sailors, who explored the seas beginning in the late 700s to around 1100, were the first Europeans to reach the Americas. The timing of the Viking forays to what they called “Vinland,” however, remained unclear. Based on artifact finds, radiocarbon dating, and Viking sagas, the settlement at L’Anse aux Meadows was thought to have briefly thrived somewhere between 990 and 1050.

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Now, thanks to that cosmic storm in 993, researchers can assuredly say that Vikings were working away at their tiny outpost in the north Atlantic exactly 1,000 years ago, in 1021, according to a study published today in the journal Nature.

While the new, more precise date will not radically alter our current understanding of the Viking presence in the Americas, it “confirms what archaeologists and previous evidence have suggested,” says Ulf Büntgen, a geographer at the University of Cambridge who was not part of the research team. “I’m really happy to see such a paper—20 years ago we wouldn’t have been able to get such data.”

Besides providing the first exact date for Viking settlement in North America, the dates also provide confirmation for tales of early voyages written down hundreds of years after the fact. “We always knew we were right around 1000, but 1021 is a huge deal,” says Davide Zori, an archaeologist at Baylor University who was not involved in the research. “This shows the [Viking] sagas are correct to within a decade. That’s pretty impressive.”

'Like a gold mine'

The new evidence comes from old samples. Dozens of radiocarbon dates taken from wooden artifacts excavated at L’Anse aux Meadows in the 1960s showed the site was about 1,000 years old. But radiocarbon dating was in its infancy at the time, and the margin of error was often measured in decades or even centuries.

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Fortunately, forward-thinking archaeologists anticipated better dating methods might be developed in the future, so they recovered and preserved hundreds of additional pieces of wood found in and around the site, storing many in deep freezers in a Canadian warehouse to prevent decay. When University of Groningen archaeologist Margot Kuitems, a co-author of the study, visited the warehouse a few years ago, she was stunned. Millennia-old wood “looked perfectly fresh, like it was put in yesterday,” she says. “It was like a gold mine.”

Kuitems wasn’t looking for the prettiest pieces, though. She and Michael Dee, a radiocarbon dating expert also at the University of Groningen, were searching for sites to test a new dating method based on tree rings. To see if they could narrow down the age of L’Anse aux Meadows, Kuitems picked four fir and juniper logs with bark still attached, all of which had been chopped and left near one of the Norse longhouses. “They’re not really artifacts or beautiful pieces made by Vikings,” Kuitems says of the pivotal samples. “They’re discarded bits of wood.”

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All four samples had a few things in common that made them perfect for Dee and Kuitems’s purposes. They were found in layers of soil alongside other Viking artifacts, connecting them to the Viking activity. They had been cut or worked with metal tools—otherwise unknown in North America at the time, and more evidence for Viking handiwork. And they all had bark still attached, clearly showing when the tree stopped growing.

There was one more thing that stood out: Three of the wood samples were from trees alive during the solar event of 993, when the cosmic storm released a pulse of radiation so powerful that it was recorded in the rings of the world’s trees. Referred to by researchers as a “cosmogenic radiocarbon event,” the phenomenon has only happened twice in the last 2,000 years.

The cosmic storm, along with a similar event in 775, left behind “spikes” that skew radiocarbon dates from wood by about a century, a fact that researchers first identified in 2012. Identifiable only by comparing radiocarbon dates from individual tree rings, the resulting anomaly creates a sort of tree ring time stamp. “When you hit the spikes it’s really clear,” says Dee, who led the new study.

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The team painstakingly sampled and radiocarbon dated more than 100 tree rings, some less than a millimeter wide, hoping to find the 993 spike in the radiocarbon age. In three of the pieces of wood they found the sharp jump they were looking for. Simple arithmetic then made it possible to figure out when Vikings felled the tree. “If you have a tree with lots of rings and have the bark edge, it’s just a question of counting,” Dee says. In this case, 28 rings separated the bark from the tree ring in which the 993 solar pulse is recorded.

“The [previous] radiocarbon dates stretch between the beginning and the end of the Viking Age,” says Dee. “We’re proving it happened by 1021 at the latest.”

Furthermore, this date corroborates two Icelandic sagas, the “Saga of the Greenlanders” and the “Saga of Erik the Red,” that recorded attempts to establish a permanent settlement in “Vinland” on the far western edge of the Viking world. Though written down in the 1200s, both sagas refer to historic events and people, allowing scholars to reconstruct a rough timeline for the voyages around 1000.

Zori agrees that the new date won’t revolutionize what we know about the Vikings in the Americas. But using the 993 cosmic radiation spike to date other sites could offer new insights, particularly where historical records can’t be easily tied to archaeological discoveries. “When you want to connect specific events with monuments or buildings, having a precise date really might change our understanding,” Zori says.

For Dee, pinning down the date creates a tangible link to the time when humanity completed its expansion around the world and met in a thickly wooded forest on the shores of the North Atlantic. “The moment the Atlantic was crossed was sort of the last step,” he says. “The date we’ve got substantiates the fact that it was real.”