Exactly 1001 years ago, a Viking took an axe to a tree. The tree — and, for that moment, the Viking — were at a place now called L’Anse aux Meadows in modern-day Newfoundland. The Viking called it Vinland; at least, that is how later Vikings recorded it in their saga accounts of the adventures of Leif Erikson and the Vikings in North America.

We know this because 1000 years later, in the fall of 2021, a team of scientists tested wood chips from the Viking’s efforts and was able to date them with startling precision to the year 1021. As the team reported in the science journal Nature, they were able to derive this precision result because of a cosmic storm that swept past Earth some decades earlier.

An Interdisciplinary Saga

Vikings and cosmic radiation storms make for a great pairing and a great example of interdisciplinary science at its most amazing, weaving threads together from historical research, archeology, nuclear physics and space science.

The story begins with a set of stories: the Icelandic Sagas, tales of Viking adventures recorded and preserved in medieval Iceland long after the Viking era ended. The saga accounts of Leif Erikson’s voyages to lands west of Greenland were regarded with some doubt until 1960, when, as Science reports, a Viking-era Norse archeological site was found at L’Anse aux Meadows.

The archeological findings confirmed that the Vikings did not simply make up their stories, but had actually reached parts of the Americas. But when it happened remained uncertain. Viking artifacts from the site could be dated on stylistic grounds, but only approximately.

An alternative method of dating ancient organic material — such as wood — relies on measuring radioactive carbon-14 from a sample and comparing it to non-radioactive carbon in the same sample. Because carbon-14 decays at a known rate, the proportions can be used to estimate when the organic material died and thus stopped absorbing carbon.

Most radiocarbon dating is only approximate. This is especially true of samples measured in the 1960s after the discoveries at L’Anse aux Meadows, when the technique was less developed. But since that time, scientists have made a couple of other important discoveries.

A Cosmic Storm Leaves Its Mark in Trees

Careful examination of the radiocarbon dating record shows that there have been occasional spikes in the proportion of radioactive carbon-14, believed to be due to bursts of cosmic rays striking the Earth. These cosmic storms probably erupted from the sun, but whatever their source, the cosmic ray bursts affected the proportion of radioactive carbon absorbed by trees around the world at that time.

One of these storms, reports ScienceAlert, can be dated to the years 992–993. Trees growing at that time show a carbon-14 spike in their annual growth ring for that year. By counting the number of growth rings between the carbon-14 spike and the bark, researchers can determine what year the tree died in.

This is how the wood chips from L’Anse aux Meadows were found to have come from trees that were chopped down in the year 1021. As chief researcher Michael Dee notes in Science magazine, the key evidence was “not some beautiful objects or Viking artwork or anything like that,” but simply “offcuts or refuse of Viking activity.” Dee also remarks on the foresight of archeologist and coauthor Birgitta Wallace, who thought to preserve wood chips from the site in a freezer.

The wood chips also show that the tree was felled with a metal ax. This detail links the chips specifically to the Vikings, since the Indigenous people of the region did not use metal axes at that time.

The Saga Continues

Radiocarbon expert Rachel Wood, who was not part of the research team, remarks that “the precision is astounding” — pinning down Norse activity at L’Anse aux Meadows not just to the Viking era, but to a specific year.

And the modern saga of rediscovering the Vikings in North America continues. At almost the same time that Nature reported the exact dating of L’Anse aux Meadows, Sci-News reported that a 14th-century monk in Milan, Italy set down an account of a land in the far North Atlantic he called Marckalada — his rendering, in medieval Latin, of Markland. This was another western island reported by the sagas, now believed to probably be Labrador.

Fourteenth-century Milan was in close contact with the great commercial center and seaport of Genoa, where Christopher Columbus would be born 100 years later. Were rumors of western Atlantic islands floating around Genoa at that time? Just as we have closed in on the date of the settlement at L’Anse aux Meadows, we may be closing in on an answer to that question, too.