Ancient DNA may rewrite the story of Iceland’s earliest settlers

The Norse may have lived in Iceland almost 70 years earlier than historians thought, and their arrival may not have been the environmental disaster that is often portrayed.

Historical accounts suggest that the first inhabitants settled Iceland in the 870s. This early migration is often described as an ecological disaster brought on by Viking raiders or Norse settlers as they cleared the island’s forests for fuel, building materials and fields. Forests now cover only 2 percent of the country.

It is difficult to obtain solid evidence of when the first settlers arrived. Archaeologists have unearthed an ancient wooden longhouse near the Stöðvarfjörður fjord in eastern Iceland, dating to around 874 AD.

Now, Eske Willerslev of the University of Copenhagen, Denmark, and colleagues examined environmental DNA (eDNA) extracted from two sediment cores drilled at Lake Tjörnin in central Reykjavík, one of Iceland’s oldest and longest-occupied settlements, to see which species were present at which time. By examining layers of volcanic ash and using radiocarbon dating and plutonium isotope analysis, the researchers established a timeline spanning from about 200 AD to the present, aligned with known historical events.

A key marker they used is known as the Landnám tephra layer, the ash and fragments left behind by a volcanic eruption around AD 877. Most evidence of human occupation in Iceland is above this layer, so it was deposited after the eruption.

“The signs below the tephra are like irrefutable proof that there was previous human activity,” says Chris Callow of the University of Birmingham, UK, who was not involved in the study.

Willerslev and his colleagues suggest that people arrived almost 70 years before this date: around 810 AD. Indeed, at this point, they saw an increase in a compound called levoglucosan, an indicator of biomass burning, as well as an increase in viruses associated with wastewater.

“If it had been 850, I wouldn’t have been so surprised, but 810 is an early number for Viking expansion into the North Atlantic,” Callow says. “Overall, it’s a nice confirmation of what we might have suspected, but it’s still quite controversial to have a date as old as 810.”

Putting together this complete environmental history of the region is phenomenal, but the evidence from such an early date is inconclusive, says Kathryn Catlin of Jacksonville State University in Alabama. “When it comes to sewage biomarkers, there’s a small increase around 800, then nothing until 1900. Where are all the indicators of humans in sewage biomarkers and the period in between?” she said. And while burning biomass can indicate the presence of people, fires can also be started by natural sources like lightning, she adds.

Willerslev and his colleagues, who declined to speak New scientistalso found that the arrival of settlers coincided with an increase in local biodiversity. DNA records suggest they took grazing cattle with them, cultivated hay meadows, and practiced small-scale barley cultivation to brew beer.

Contrary to the conventional idea of ​​rapid deforestation, pollen eDNA revealed that birches and willows expanded during the colonization period. For example, birch pollen grains increased five-fold between 900 and 1200 AD, which researchers believe may be due to deliberate management, keeping livestock away from the trees to ensure settlers continued to have easy access to building and firewood.

“It’s the nail in the coffin of this old, trite story of the Vikings arriving in Iceland and then, all of a sudden, ‘oh no, the environment is destroyed,'” says Catlin.

Notable numbers of sheep, cattle, pigs, and horses do not appear until several decades after initial colonization, which Willerslev and colleagues suggest is because it would have taken about 20 years to build up herds large enough to be detectable in eDNA records.

Callow suggests another reason: It could be that early people didn’t bring many animals with them because they came just for the summer season in search of walrus ivory. “They could have killed a few walruses and then gone home,” he said.

The eDNA suggests that a pronounced loss of biodiversity, including birches and willows, did not occur until after 1200. Willerslev and colleagues suggest that this was not associated with the presence of settlers, but with climate cooling linked to the Little Ice Age. – a period of colder conditions from around 1250 to 1860 – as well as volcanic eruptions and storm surges.