May 19, 2022

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New Evidence Supports Coastal Route for Peoples of the Americas

New Evidence Supports Coastal Route for Peoples of the Americas

Transport of rocks by glaciers.

Transport of rocks by glaciers.
Photo: Ian Watkinson / EGU

The opening of the ice-free corridor connecting Beringia inland in North America likely opened thousands of years after the first human migrations to the continent, according to new evidence. Scientists say the discovery should bolster the idea that ancient humans traveled to the Americas along a coastal route, but other researchers remain skeptical.

new Research The Proceedings of the National Academy of Sciences reports the emergence of an ice-free corridor connecting Beringia with the Great Plains about 13,800 years ago. Previous estimates indicated that the pass appeared about a thousand years ago, as the last ice age was drawing to a close. according to Previous archaeological work, the first human migrations to the North American continent occurred about 15,000-16,000 years ago, and possibly 20,000 years ago. The authors of the new paper say their findings strengthen the hypothesis of coastal migration, in which the first people to reach the Americas traveled along the Pacific coast.

“The ice-free corridor has always played a key role in hypotheses regarding the population of the Americas, but our results provide strong evidence that the ice-free corridor has not been open and accessible for this purpose,” said Jury Clark, first author of the new paper and a researcher from the College of Science Land, Ocean, and Atmosphere at Oregon State University, explained in an email. “This has been inferred before, but the evidence for the age of the ice-free passage opening was too uncertain to be used conclusively to address this question one way or the other.”

Clark and her colleagues used a dating method known as “cosmic nuclide surface exposure dating,” which works by “dating a rock deposited by the ice sheet when it first pulled out of the site, with the date telling us how long ago that rock was deposited first by the ice sheet.” And exposed to the atmosphere, “In simpler terms, they calculated cosmic ray strikes to determine how long a rock remained on Earth’s surface.

In an email, Ben Potter, an archaeologist from the Center for Arctic Studies at Liaocheng University in China who was not involved in the new research, said he was “not convinced” by the paper. Cosmic exposure dating provides minimum ages, not maximum ages, he said, adding that researchers have failed to provide reasons for rejecting other efforts so far to unlock the ice sheets, including Research It shows the emergence of a de-glaciated, lake-free gorge at least 15,000 years ago.

Determining the timing of a land route linking Eurasia and North America is important, as it bears implications for the Clovis first hypothesis. This theory states that people living in Alaska and Yukon traveled south along the interior to the Great Plains, where they established the Clovis culture, named for their distinctive stone tools. Recent archaeological and genetic evidence has challenged this theory, pointing instead to a pre-Clovis migration to the Americas before the massive ice sheets of the Cordilleran and Laurentide retreated. “Resolving this debate” about immigration routes “is important to addressing questions about when and how the first Americans arrived,” the scientists wrote in the new study.

Clark said that previous studies using other dating techniques are limited in that they only show that the ice-free pass appeared shortly before the acquired date. For example, “The radiocarbon date on a piece of organic fossil material only dates to the time that fossil material lived, which could be any time after the ice-free passage opened – we simply don’t know how long before the date the foundation opened International Finance”. Relative to previous research that used exposures to the universe dating back to the history of the ice-free corridor, she added, it is limited in terms of geographic scope and the amount of samples analyzed.

For the new analysis, Clark and her team studied icy displaced rocks along 745 miles (1,200 kilometers) from the Cordilleran-Laurentide ice sheet suture region, allowing them to sample from 64 exposures of the universe. She explained that the team was able to “evaluate several potential uncertainties in the dates and derive a robust average date for each location.” The use of cosmic rays until the date of the rocks might seem odd, but Clarke likened it to a suntan.

“When the rock is first deposited by retreating ice sheets, it is exposed to the atmosphere for the first time, including cosmic rays that come from space, travel through the atmosphere and strike the Earth’s surface,” Clark explained. “This would be similar to sitting outside for the first time after being indoors all winter and starting to get exposed to the sun. Once the rock is first exposed, cosmic rays penetrate the rock and produce new elements – cosmic nuclides – in the rock, so over time, the concentration of these increases Elements “.

Scientists can measure the concentration of these elements in the lab, and since they know how many new elements are being produced each year, they can “calculate the time since the rock was first exposed by the retreat of the ice sheet,” Clark said. “Some people may question our dating method, but we feel confident that any adjustments to our ages will not change our bottom line,” Clark said, adding, “We are also very confident in our results.”

Potter does not share this confidence, saying that the team only used one standard deviation to explain when two were required. When using the more conservative value, the new evidence suggests a minimum age for the opening of the ice sheets for some time between 13,000 and 15,600 years, he said. This range of uncertainty is consistent with several optically stimulated and infrared stimulated fluorescence dating efforts that suggest the emergence of an ice-free corridor at least 15,000 years ago, Potter said.

One of the main findings of the new paper is that a viable corridor for the first wave of humans to enter North America by land did not exist until at least 13,800 years ago, and that humans who migrated earlier must have done so by traveling along the coast of North America. Pacific. This may not be the case. Not so surprising given other evidence, such as 15,000-year-old archeology Guide At Cooper’s Ferry in Idaho.

Potter thinks we shouldn’t rule out the Inner Way just yet. He said that “there is no widespread consensus that the oldest ages of the coals scattered at Cooper Ferry are related to occupations”, dating from 11,500 and 14,000 years ago. Thus, “the ice-free passage cannot be ruled out as a possible route to early unmistakable sites south of the ice sheets” after 15,000 years, Potter wrote. As he also points out, there are still no unequivocally dated sites along the North Pacific Coastal Route 12,600 years ago, and none from the Kuril Islands to the Aleutians and south-central Alaska on that date 9,000 years ago, which is a fair point.

Clark seems to agree on this last issue. “Although we have taken up one question about the first inhabitants of the Americas, there is still much to learn about whether they actually came down the coastal road and, if so, how they traveled—we need to find archaeological sites from this region,” she tells me. in her email.

The question of when an inner passage appeared and how early humans were able to make their way to the continent remains unresolved. As in archeology, we simply need more evidence if we want to truly understand this remarkable period in human history.

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