6:19 p.m. – Cosmic radiation sheds light on the passage of the Vikings in America

Scientists have been able to date precisely, to the year 1021, the presence of Vikings on the North American continent after their crossing of the Atlantic, thanks to dated cosmic radiation, and of which they have detected traces in pieces of wood. on the site.

It has long been known that Scandinavian sailors were the first Europeans to land there, around the year 1000, long before Christopher Columbus, which made landfall further south and almost five centuries later.

To this day, the only known site of their occupation remains Anse aux Meadows, a bay in the far north of the island of Newfoundland, where the foundations of eight timber-frame constructions remain.

But as the study published in Nature on Wednesday noted, traditional carbon-14 dating over the past century is more than imprecise, spanning more than 250 years. However, everything indicates a brief and sporadic occupation of the place, according to archaeological remains and the “Sagas”, these semi-legendary texts narrating the epics of the Vikings.

The team led by Michael Dee and Margot Kuitems, respectively professor of isotope chronology and archaeologist at the Center for Isotopic Research at the Dutch University of Groningen, circumvented the obstacle with an original method.

The Earth is constantly subjected to cosmic radiation, “which continuously produces carbon-14 (a heavier and much rarer form than the carbon atom) in the upper atmosphere,” Margot Kuitems told AFP. This form of carbon will “enter the carbon cycle, which is taken up by plants through photosynthesis.”

Sometimes the radiation is much more powerful: these cosmic radiation “events” abruptly raise the level of carbon-14 in the atmosphere.

– Solar storm –

A Japanese study isolated two such “events”, in 775 and 993, the traces of which remain in trees whose age was well known. The sudden rise in carbon-14 was found on the dates in question in their growth rings, those circles that we see on a cut trunk and that help determine the age of the tree.

Margot Kuitems’ team sought, using a mass spectrometer, the trace of the event of 993 in three samples of pieces of wood taken from the Anse aux Meadows site. Canadian experts had determined that these pieces had been worked there by the occupants with iron tools.

“When we measured the carbon-14 concentration in a series of dark circles, we found a sharp rise on one of them, and we were sure that it corresponded to the year 993”, says the scientist. . It was then enough to count the number of rings between the ring of the “cosmic event” and the last one located before the bark, to determine the date on which the tree was felled. Answer: the year 1021.

The measurement worked for two pieces of wood, which scientists were even able to pinpoint as belonging to a tree felled in the spring, and the other to the summer-fall.

The Center for Isotopic Research is at the forefront of this original method of archaeological dating. He signed a first study on the subject in 2020, precisely dating an archaeological structure in southern Siberia, using the cosmic event of 775.

According to Ms. Kuitems, there is today a “consensus” to explain these peaks of cosmic radiation by a “solar event, like a solar storm”.

Another peak in AD 660 has recently been confirmed, and could in turn serve as a time “marker”, thanks to the continuous improvement in the accuracy of mass spectrometers.

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