Five hundred years before Columbus sailed the ocean blue, a Native American woman may have voyaged to Europe with Vikings, according to a provocative new DNA study.

Analyzing a type of DNA passed only from mother to child, scientists found more than 80 living Icelanders with a genetic variation similar to one found mostly in Native Americans. (Get the basics on genetics.)

This signature probably entered Icelandic bloodlines around A.D. 1000, when the first Viking-American Indian child was born, the study authors theorize. (Related: "Vikings' Barbaric Bad Rap Beginning to Fade.")

Historical accounts and archaeological evidence show that Icelandic Vikings reached Greenland just before 1000 and quickly pushed on to what is now Canada. Icelanders even established a village in Newfoundland, though it lasted only a decade or so (regional map).

The idea that a Native American woman sailed from North America to Iceland during that period of settlement and exploration provides the best explanation for the Icelanders' variant, the research team says.

"We know that Vikings sailed to the Americas," said Agnar Helgason of deCODE Genetics and the University of Iceland, who co-wrote the study with his student Sigrídur Ebenesersdóttir and colleagues. "So all you have to do is assume … that they met some people and ended up taking at least one female back with them.

"Although it's maybe interesting and surprising, it's not all that incredible," Helgason added. "The alternative explanations to me are less likely"—for example the idea that the genetic trait might exist independently, undiscovered, in a few Europeans.

The study authors themselves admit the case is far from closed. But University of Illinois geneticist Ripan Malhi—an expert in ethnic DNA differences who wasn't part of the project—agreed that the report holds "strong genetic evidence for pre-Columbian contact of people in Iceland with Native Americans."

Dating the DNA Signature

Through genealogical research, the study team concluded that the Icelanders who carry the Native American variation are all from four specific lineages, descended from four women born in the early 1700s.

Those four lineages, in turn, likely descended from a single woman with Native American DNA who must have been born no later than 1700, according to study co-author Ebenesersdóttir.

The genealogical records for the four lineages are incomplete before about 1700, but history and genetics suggest the Native American DNA arrived on the European island centuries before then, study co-author Helgason said.

He pointed out that Iceland was very isolated from the outside world in the centuries leading up to 1700, so it's unlikely that a Native American got to the island during that period.

As further evidence, he noted that—though the Icelanders share a distinct version of the variation—at least one lineage's variation has mutated in a way that would likely have taken centuries to occur, the researchers say.

This unique signature suggests that, in Helgason's words, the Native American DNA arrived in Iceland at least "several hundred years" before 1700.

DNA Evidence Fragmented

Despite the evidence, for now it's nearly impossible to prove a direct, thousand-year-old genetic link between Native Americans and Icelanders.

For starters, no living Native American group carries the exact genetic variation found in the Icelandic families.

But of the many known scattered versions that are related to the Icelandic variant, 95 percent are found in Native Americans. Some East Asians, whose ancestors are thought to have been the first Americans, carry a similar genetic pattern, though.

The Inuit, often called Eskimos, carry no version of the variant—a crucial detail, given that Greenland has a native Inuit population.

Helgason speculates that the precise Icelandic variation may have come from a Native American people that died out after the arrival of Europeans.

It's possible, he added, that the DNA variation actually came from mainland Europe, which had infrequent contact with Iceland in the centuries preceding 1700. But this would depend on a European, past or present, carrying the variation, which so far has never been found.

(See pictures of Native American lands in National Geographic magazine.)

History Not Much Help?

Complicating matters, the historical record contains no evidence that Icelandic Vikings might have taken a Native American woman back home to their European island, scholars say.

"It makes no sense to me," said archaeologist and historian Hans Gulløv of the Greenland Research Centre in Copenhagen.

For one thing, experts say, nothing in excavations or the Icelandic sagas—thought to be rooted in fact but not entirely reliable—suggests a personal alliance of the kind reported in the new study, published online November 10 in the American Journal of Physical Anthropology.

The Saga of Erik the Red does tell of four Skraeling boys—the Norse term for the American Indians—who were captured by an Icelandic expedition and taken back to Greenland, said Birgitta Wallace, an emeritus archaeologist for Parks Canada who has written extensively about the Norse.

But Icelanders spent little time in North America, and their relations with the people they found living there seem to have been mostly hostile, she said. The stories "talk in not very flattering terms about [Native Americans'] looks," Wallace said.

One saga, she added, tells of explorers "who found some sleeping natives—and they just killed them."

Time to Rewrite Viking History?

"What we have is a big mystery," study co-author Helgason admitted.

It won't be solved, he said, until the DNA pattern's origins are nailed down, perhaps through the study of ancient DNA—for example, if an ancient Native American bone is found with DNA closely matching the Icelandic variant.

But at least one skeptic suggests it's a mystery worth pursuing.