Viking Artifacts Give Precise Date for Europeans’ Earliest Presence in North America

The artifacts—including a tree stump, a branch and a block of timber all splintered by the swing of a metal ax—were found at L’Anse aux Meadows near the northern tip of Newfoundland, the only verified Viking settlement on the continent, and analyzed via a new radiocarbon dating technique.

Researchers have long known that Vikings reached North America near the end of the first millennium. In the 1960s, archaeologists working at L’Anse aux Meadows unearthed the ruins of eight wood-framed peat buildings built in a style common among the Norse of the Middle Ages, along with hundreds of wooden, bronze and bone artifacts. No more than 40 people are believed to have lived there, perhaps refitting the Viking long ships for voyages home.

Until now, however, scholars could only make educated guesses about when Vikings first anchored in Vinland, as the voyagers called the verdant far shore of the Atlantic, or how long they stayed. They had to rely on Icelandic sagas, which combine the exploits of historical figures and mythological characters, as well as conventional radiocarbon dating techniques that are accurate only to within 200 to 300 years.

Efforts to reconstruct the early Viking voyages have also been dogged by hoaxes and forgeries. For almost 50 years, for example, scholars have debated the authenticity of a chart of the North American coastline southwest of Greenland that some said dated to the 15th century and which seemed to buttress the idea that Vikings were the first Europeans to reach North America. Last month, Yale University, which owns the so-called Vinland Map, announced that it is a 20th century fake.

The new research, conducted by scientists in Canada and Germany as well as the Netherlands, may put to rest lingering doubts about when the Vikings arrived in North America.

”It proves when they were there,” said Anders Winroth, a University of Oslo historian and the author of the “The Age of the Vikings,” a book published in 2014. “It is refreshing and exciting to have an exact date.” Dr. Winroth wasn’t involved in the research effort.

To pinpoint the year that Vikings occupied the site, the scientists scoured the ancient settlement for wooden artifacts, hoping to find any made from trees that had grown during an unusually intense burst of cosmic radiation known to have occurred in the year 993. The barrage of charged particles, perhaps triggered by a supernova or a mammoth solar storm, flooded Earth’s atmosphere with carbon-14, a radioactive isotope commonly used in the dating of ancient artifacts.

In normal times, carbon-14 is created in the upper atmosphere at a fairly constant rate and then absorbed by plants growing on the ground below. The flare in 993 caused a roughly 20-fold spike in levels of the isotope—evidence of which can be detected in the annual growth rings of any tree alive at the time, like a time stamp on a digital recording.

These charged particle storms are so rare they make for unambiguous dating. Only one other such event, called a Miyake event, has been detected so far. That radiation burst, which seems to have hit between 774 and 775, produced the largest and most rapid rise in carbon-14 ever recorded, according to scientists.

“Any tree growing in the world in 993 will have embedded this rich carbon level,” said Dr. Dee, who helped pioneer the use of the carbon-14 spikes for dating. “There will be this jump.”

Dr. Dee and his colleagues tested wood specimens that showed the distinctive cut marks left by a metal blade—an implement unknown among the indigenous people of the era, who used only stone tools. Using the carbon spike as a reference point, they counted the tree rings in each specimen until they reached the bark, indicating the year the tree was cut down—in this case 1021.

“We have three wooden artifacts from three different trees and they all give the same date, “ Dr. Dee said. “This is really a big change in the precision that is achievable with scientific dating.”

Write to Robert Lee Hotz at sciencejournal@wsj.com