How Did the First Americans Spread Across the Continent?

New theories on what happened after Indians reached Alaska from Asia.

ByABC News
June 26, 2012, 5:24 PM

June 27, 2012 — -- A serendipitous discovery on a remote island off the coast of Alaska may provide a turning point in the debate among scholars over how the First Americans arrived in the new world.

For decades, archaeologists have believed that early hunters traveled across a wide swath of land that linked Siberia with Alaska during the last Ice Age, moved down into the Great Plains and eventually populated the New World.

But there's a problem, according to many scholars. The only route from the far north to what is now the continental United States was through a corridor between two huge ice fields that spanned the eastern and western regions of the continent. That corridor probably didn't thaw enough for human passage until about 13,000 years ago, and some well documented settlements in South America are believed to be at least 14,000 years old.

So over the last few decades, a number of archaeologists have argued that the First Americans must have traveled along the coast if they arrived in Peru and Chile at least 1,000 years before the corridor opened. But how could they if the coastal route was blocked by ice?

According to research published in the current issue of Quaternary Science Reviews, the wall of ice that supposedly blocked any maritime explorers disappeared nearly 17,000 years ago, giving those immigrants an extra couple of thousand years to make it down to South America. They may have walked along the beach when they could, and built crude vessels when they could travel only by water.

And it's the only way, so far, to explain how they got to South America 14,000 years ago. The other possibility, that they somehow sailed across the Atlantic or Pacific, has not been well accepted by archaeologists.

This discovery isn't going to end the debate. But it's a critical piece of evidence that until now has been missing.

"We're not saying people definitely did that," Nicole Misarti of Oregon State University in Corvallis, lead author of the study, said in a telephone interview. "All we're saying is the barrier was not there."

Misarti led a large interdisciplinary team on an expedition to Sanak Island, an uninhabited chunk of land about 700 miles west of Anchorage. Ironically, the researchers were studying early runs of salmon, not human migration, when they stumbled across some information that was, frankly, much more interesting than what they had gone there to study.

In 2004, the researchers drilled into the land beneath three lakes on the island to collect core samples containing sediments thousands of years old. The samples were later sent to Lawrence Livermore National Laboratory for dating.

"The radio carbon dates trickled in slowly over a couple of years and when we looked at the age all we could say was 'wow,'" Misarti said in a telephone interview. The samples were much older than had been expected, because the island was supposed to have been buried under glaciers until about 15,000 years ago.

Yet the samples told the story of an island covered with dry plant species like heathers and sagebrush and grassland tundra. Far from being frozen, it was covered with vegetation 2,000 years earlier than had been thought.

"All of a sudden, this big barrier that was supposed to be a 200-meter high ice sheet might not actually have been there," Misarti added.

But would those early explorers, believed to have originated in the orient and Siberia, have had the technology to build boats that could travel great distances? That's not as far fetched as it seems.

In "Guns, Germs, and Steel," geographer Jared Diamond notes that around 40,000 years ago humans colonized Australia and New Guinea and a wide range of islands that they could only reach by sea. So there are precedents of long voyages many years before the First Americans arrived on this continent.