In 1427, the Portuguese navigator Diogo de Silves first set foot on an uninhabited, Sun-kissed island with white sand beaches, crystal blue bays, and dramatic cliffs, proclaiming it Santa Maria Island. Later arrivals by other Portuguese explorers revealed it to be the southeasternmost island of the Azores archipelago, which lies about 1368 kilometers west of Portugal’s coast.
According to a new study of lake sediment cores, however, the Portuguese may not have been the first people to reach the island paradise: Viking seafarers may have arrived some 700 years earlier than de Silves and his crew. Any Vikings were long gone by the time Portuguese sailors arrived, the authors note, but some Norse rodent stowaways may have left a lasting genetic mark on the island.
The paper is a welcome addition to the sparse data on the Azores prehistory, says Jeremy Searle, an evolutionary biologist at Cornell University. His team proposed a Norse connection to the island in 2015, based on genetic similarities between Azorean and northern European mice. “To actually have firm data supporting that is obviously pretty gratifying.”
Conclusive archaeological evidence of humans in the Azores is sparse and only dates back to the early 15th century. In recent years, a few studies hinted at even earlier occupation, although it wasn’t clear who these earlier settlers were or when they arrived. About 10 years ago, Pedro Raposeiro, an ecologist at the University of the Azores, Ponta Delgada, and colleagues set out to collect cylindrical cores of sediment from five lakebeds around the archipelago as part of an effort to detail the region’s climate history. As particles in the air settle to the bottom of the lake, they form datable layers. The researchers suspected they would find signs of human disturbance—pollen from nonnative crops, spores from fungi that grow on livestock dung—dating back to the early 1400s. And they did.
But the researchers were surprised to find these signals extended even further back in time. In a sedimentary layer dating to between 700 C.E. and 850 C.E. taken from Peixinho Lake on the Azores’s Pico Island, the researchers saw a sudden uptick of an organic compound called 5-beta-stigmastanol, which is found in the feces of ruminants such as cows and sheep. They also saw an increase in charcoal particles and a dip in the abundance of native tree pollens, perhaps pointing to humans cutting down and burning trees to clear space for livestock to graze, Raposeiro says.
A similar signal shows up in cores from Caldeirão Lake on the Azores’s Corvo Island dating to about 100 years later. Pollen from a nonnative ryegrass shows up in layers from Pico Island dating to about 1150, and at 1300 on São Miguel Island, also part of the archipelago.
Taken together, the results suggest humans were occupying and exploiting the natural resources of the Azores at least 700 years earlier than historians have traditionally believed, the team reports today in the Proceedings of the National Academy of Sciences.
It’s not clear when these earliest human settlers of the Azores disappeared, but the Portuguese sailors who explored the islands in the 1400s described the islands as pristine.
Who were those first ancient mariners? “Our best guess is the Norse,” who were accomplished and adventurous seafarers, Raposeiro says. By as early as 789, there are records of Vikings sailing and plundering up and down the coasts of northern and western Europe.
Secondly, climate simulations for this time suggest the dominant winds in the North Atlantic Ocean blew from the northeast. Those winds would have put Viking ships heading southwest from their Scandinavian homelands more or less directly into the path of the Azores, Raposeiro says. Those same winds, he adds, would have made it comparatively difficult for sailors coming from the Portuguese mainland to reach the Azores.
Finally, as Searle and colleagues documented in 2015, Azorean house mice share a substantial amount of DNA with house mouse populations that originated in northern Europe. The mice could have hitched a ride on the Viking ships and encountered an island with plentiful resources and few competitors or predators, says Searle, who was not involved in the latest study. The mice are like “living artifacts,” of a Viking presence, he says.
The study convincingly demonstrates that people were on the Azores as early as about 700, says Simon Connor, a geographer at the Australian National University who studies the paleoecology of the archipelago. But he isn’t yet persuaded they were Norsemen.
Connor says unfavorable winds may not have prevented determined sailors from the Portuguese mainland from reaching the archipelago. As for the mice, thanks to widespread trade routes, a mouse from Scandinavia could easily have boarded a ship in what today is Portugal and sailed over to the Azores. “Certainly, it’s possible it was the Norse,” Connor says. “The Vikings were great, great mariners. … But it could have been anyone.”