In ancient boulders, new clues about the story of human migration to the Americas

In ancient boulders, new clues about the story of human migration to the Americas
Infographic showing study sites. Credit: Bob Wilder/University at Buffalo

When and how did the first people come to the Americas?

The conventional story says that the earliest settlers came via Siberia, crossing the now-defunct Bering land bridge on foot and trekking through Canada when an ice-free corridor opened up between massive ice sheets toward the end of the last ice age.

But with recent archaeological evidence casting doubt on this thinking, scientists are seeking new explanations. One dominant, new theory: The first Americans took a coastal route along Alaska's Pacific border to enter the continent.

A new geological study provides compelling evidence to support this hypothesis.

By analyzing boulders and bedrock, a research team led by the University at Buffalo shows that part of a coastal migration route became accessible to humans 17,000 years ago. During this period, ancient glaciers receded, exposing islands of southern Alaska's Alexander Archipelago to air and sun—and, possibly, to human migration.

The timing of these events is key: Recent genetic and archaeological estimates suggest that settlers may have begun traveling deeper into the Americas some 16,000 years ago, soon after the coastal gateway opened up.

The research will be published online on May 30 in the journal Science Advances.

"People are fascinated by these questions of where they come from and how they got there," says lead scientist Jason Briner, Ph.D., professor of geology in UB's College of Arts and Sciences. "Our research contributes to the debate about how humans came to the Americas. It's potentially adding to what we know about our ancestry and how we colonized our planet."

"Our study provides some of the first geologic evidence that a coastal migration route was available for early humans as they colonized the New World," says UB geology Ph.D. candidate Alia Lesnek, the study's first author. "There was a coastal route available, and the appearance of this newly ice-free terrain may have spurred early humans to migrate southward."

In ancient boulders, new clues about the story of human migration to the Americas
University at Buffalo Ph.D. candidate Alia Lesnek works at Suemez Island. Credit: Jason Briner

The findings do not mean that early settlers definitely traversed Alaska's southern coast to spread into the Americas: The project examined just one section of the coast, and scientists would need to study multiple locations up and down the coastline to draw firmer conclusions.

Still, the work is exciting because it hints that the seafaring theory of migration is viable.

The bones of an ancient ringed seal—previously discovered in a nearby cave by other researchers—provide further, tantalizing clues. They hint that the area was capable of supporting human life at the time that early settlers may have been passing through, Briner says. The new study calculates that the seal bones are about 17,000 years old. This indicates that the region was ecologically vibrant soon after the ice retreated, with resources including food becoming available.

Co-authors on the research included Briner; Lesnek; Charlotte Lindqvist, Ph.D., an associate professor of biological sciences at UB and a visiting associate professor at Nanyang Technological University; James Baichtal of Tongass National Forest; and Timothy Heaton, Ph.D., of the University of South Dakota.

A landscape, touched by ice, that tells a story

To conduct their study, the scientists journeyed to four islands within the Alexander Archipelago that lie about 200 miles south/southeast of Juneau.

The team traveled by helicopter to reach these remote destinations. As soon as the researchers arrived, Briner knew that the islands had once been covered by ice.

"The landscape is glacial," he says. "The rock surfaces are smooth and scratched from when the ice moved over it, and there are erratic boulders everywhere. When you are a geologist, it hits you in the face. You know it immediately: The glacier was here."

To pinpoint when the ice receded from the region, the team collected bits of rock from the surfaces of boulders and bedrock. Later, the scientists ran tests to figure out how long the samples—and thus the islands as a whole—had been free of ice.

In ancient boulders, new clues about the story of human migration to the Americas
University at Buffalo geologist Jason Briner collecting rock samples on Dall Island, Southeast Alaska. The samples, collected from mountain summits directly facing the Pacific Ocean (pictured in the background), were used to determine when Ice Age glaciers retreated from the area, making it available as a migration route. Credit: Charlotte Lindqvist

The researchers used a method called surface exposure dating. As Lesnek explains, "When land is covered by a glacier, the bedrock in the area is hidden under ice. As soon as the ice disappears, however, the bedrock is exposed to cosmic radiation from space, which causes it to accumulate certain chemicals on their surface. The longer the surface has been exposed, the more of these chemicals you get. By testing for these chemicals, we were able to determine when our rock surfaces were exposed, which tells us when the ice retreated.

"We use the same dating method for huge boulders called erratics. These are big rocks that are plucked from the Earth and carried to new locations by glaciers, which actually consist of moving ice. When glaciers melt and disappear from a specific region, they leave these erratics behind, and surface exposure dating can tell us when the ice retreated."

For the region that was studied, this happened roughly 17,000 years ago.

The case for a coastal migration route

In recent years, evidence has mounted against the conventional thinking that humans populated North America by taking an inland route through Canada. To do so, they would have needed to walk through a narrow, ice-free ribbon of terrain that appeared when two major ice sheets started to separate. But recent research suggests that while this path may have opened up more than 14,000 years ago, it did not develop enough biological diversity to support human life until about 13,000 years ago, Briner says.

That clashes with archaeological findings that suggest humans were already living in Chile about 15,000 years ago or more and in Florida 14,500 years ago.

The coastal migration theory provides an alternative narrative, and the new study may mark a step toward solving the mystery of how humans came to the Americas.

"Where we looked at it, the coastal route was not only open—it opened at just the right time," Lindqvist says. "The timing coincides almost exactly with the time in human history that the migration into the Americas is thought to have occurred."


Explore further

Spear points prove early inhabitants liked to travel

More information: A.J. Lesnek el al., "Deglaciation of the Pacific coastal corridor directly preceded the human colonization of the Americas," Science Advances (2018). advances.sciencemag.org/content/4/5/eaar5040
Journal information: Science Advances

Citation: In ancient boulders, new clues about the story of human migration to the Americas (2018, May 30) retrieved 19 July 2019 from https://phys.org/news/2018-05-ancient-boulders-clues-story-human.html
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May 30, 2018
Unfortunately the best evidence is now hidden beneath 80+ meters of ocean.
An accelerated phase of sea level rise occurred between 14,600 to 13,500 years before present, when sea level increased by some 16 to 24 m as the glaciers melted.

May 30, 2018
I agree with the speculations, that prehistorical humans did a lot more traveling and further by boats and canoes. Rowed or poled. Than we have imagined.

As S_F points out, most of the coastal routes are now concealed by rising oceans. Those early voyageurs up rivers and streams? Their camp sites, close to water were probably scoured away by thousands of floods. Or dug up or covered over by later human settlements.

Another reason to consider the viability of travel along the shores would be availability of food sources and fuel to cook with.

With the harsh climate conditions, the travelers would find maritime fish, shellfish and aquatic mammals a lot more reliable than inland game.

In addition, the pinnipeds and cetaceans were food, hides, oil for cooking. Ivory, bone, shells were an entire industry of sustenance and useful tools.

May 30, 2018
Nevermind that it's been genetically proven that the "Europeans" of today have absolutely no relation at all to the first people in Europe. Nevermind that "Europeans" of today only have 'white' skin now because they were conquered and replaced by light-skinned people of the Middle East around 9000 years ago. Nevermind the decades past where 'white' "supremacists" have been continuously asserting that they are the direct descendants of the first people in Europe and that those people were always 'white'.

I thought the first people of the America's was supposed to be THE WHITE RACE and it's supposed to have all sorts of political implications?

May 30, 2018
I keep hearing "experts" whisper "...by sea, by sea." Only problem is that none of the researchers/theoreticians/experts is ever described as having any open ocean sailing experience. NEVER! WTF? They also never mention having consulted modern long distance sailors for their advice/opinion. NEVER! Of COURSE people traveled the world by SAILboat (no rrwillsj, not rowed, not poled), but apparently that's apostasy. Ah well, what can you expect of "scientists"? Wake me when that understanding becomes part of their "science". Or, just call me!! What I can do was possible many tens (or hundreds) of thousands of years ago. Remind me again about those college entrance exams that select (or is that cull) smart people.

May 31, 2018
salty, you have some good points there but that popeyed squint of yours has resulted in myopia.

Before sails were invented? Where ahoy is the evidence that it was tens or hundreds of thousands of years ago?

You are talking about transoceanic travel. The researchers for this project are talking about hugging the shore. In short, probably mostly daylight hops, all the way from Siberia. Along the North-West shore, then the Californias, Mexico, Central America and down to Chile.

This entire route is popular today for experienced and professionally led kayakers. And as a major trade route all through the Meso American Era.

Until the compass and astrolabe? Only a few sailing ships would dare to leave sight of land.

I recommend reading "Longitude" by Dava Sobel. It will clarify the difficult realities of applying science to the craft of sailing. And make you wonder if hubris is a requirement for being an Admiral? The title sure didn't do Columbus any damn good!

May 31, 2018
Only problem is that none of the researchers/theoreticians/experts is ever described as having any open ocean sailing experience. NEVER! WTF? They also never mention having consulted modern long distance sailors for their advice/opinion. NEVER!
@Salt
disregarding Heyerdahl and Jon Erlandson for the moment... you mean like this?
https://www.sea.e...igration

https://en.wikipe...e%CA%BBa

not to be rude but... this is something that more than a few scientists are researching

more to the point, this isn't just isolated to the Micro- and Polynesian boats as I've seen research on Egyptian, Middle Eastern, American Indian (Various), Chinese and other Asiatic nations sea-faring vessels. From reproductions and tests to fascinating finds all over the world... most of which include not only sailors but all the related fields like sailmaking and boatbuilding

May 31, 2018
If it doesn't put food on the table what is it worth? So, my question is, have Captain Stumpy or rrwillsj done long distance voyaging in a sail boat. Put differently, have either of you walked a full ten miles directly along any coast? I'm not saying small boats didn't come into play, rather that somewhat larger vessels and the long distances that they can take a group of people seldom get discussed. We must make a distinction between land people (land lubbers), who only go as passengers on one or two voyages looking for more land, from those who are married to the sea. As for the invention of sails, they can't find the first time they were used because they have been in use for tens of thousands of years and the climate near the ocean turns things into mush pretty quickly so the evidence is sparse, but there is some.'Scientists' are researching generally means they "are looking into it", which carries the implication they are starting from scratch. Why not talk to people who know?

May 31, 2018
The article above does not even mention boats. The word is simply not there. It is left to the reader to decide if the people walked, did coastal hops or came from a long distance. My irritation comes directly from the fact that such researchers propose a 'route' for people and then don't even bother to explain what they mean.Obviously they can't tell if this was a painfully slow travel by people moving house every ten years or quickly by small boat along the coast, but they don't even discuss any possibilities.Are we to believe they are agnostic or just ignorant? The 'simple' people of the ancient past were not simple. Certainly they were more sophisticated than land lubbers today. Who were the 'scientists' consulting to come up with their theories? Anybody at all?

May 31, 2018
I made a small mistake. This article does have the word "seafaring". In an earlier article by Lesnek, there was no mention at all. Still, my observations and questions stand. By the way, there is firm evidence of people in the southwest of the U.S. 30,000 years ago. How did they get there? There are potentially even older dates for people in South America. Did they come across a land bridge from Antarctica? /s After all, the Piri Reis map shows an ice free continent, drawn before they had complete maps of North and South America.

May 31, 2018
If it doesn't put food on the table what is it worth?
@Salt
WTF?
So, my question is, have Captain Stumpy or rrwillsj done long distance voyaging in a sail boat. Put differently, have either of you walked a full ten miles directly along any coast?
to answer you:
1- Yes, I've taken long distance voyaging on a small sailboat, but not over 12K miles one way
Personally, I am a fan of the Junk, but my uncle owned a Ketch and a Schooner, which is what we used

2- re: walked the coast - yes. extensively. multiple coastlines, multiple nations
We must make a distinction between land people (land lubbers)... from those who are married to the sea
I was answering your question with links because you're unaware that scientists were actually "having any open ocean sailing experience" and "consult[ing] modern long distance sailors" [sic] as well as ancient, traditionally trained long-distance sailors
my observations and questions stand.
not really

May 31, 2018
"Only a few sailing ships would dare to leave sight of land."

That "few" included Chinese, Indian and Arab traders, Polynesian, African and Carib travelers, and possibly South American rafters. Almost every scrap of habitable land on the planet was occupied, including places that were days/weeks from the closest land.

Your "few sailing ships" refers only to the European sailing tradition, primitive ships from a backwards corner of the globe ruled by barbarians.

May 31, 2018
@salt cont'd
My irritation comes directly from the fact that such researchers propose a 'route' for people and then don't even bother to explain what they mean
no, that is also incorrect. They specifically call out the route in the study that is linked

I think your problem is with the article above, which you somehow confused with the study linked in the "more information" part - if you're making judgements on the data in the study based upon the article then you need to understand that an article is the author's interpretation of the science presented

I would recommend reading the study fully before commenting further as that would allow you to call out specifics in the data that may be answered (through the references or other means)

PS - the study is also focused and not representative of all possible migration routes

May 31, 2018
Cusco, we need to separate what we know now from what earlier sailors, of many levels of competency, knew then.

For all his errors of geography (which were considered cutting-edge in his age)

Columbus does deserve credit for pressing ahead to cross the uncharted Atlantic. Vainly attempting to discover the route to semi-mythical Cathay.

Charts were damn few & notoriously unreliable. The simplicity of the navigation tools were made up with the experienced skill of the Sailing Master. Who had been to & returned alive from the destination your merchant house wanted to trade with.

As supercargo, you sent expendable son-in-laws. If they failed to return? At least the cargo was profitable. If the boy wonder survived? If he was smart enough to shut up & listen to the Sailing Master & other veteran sailors? He might have chance at his own ship.

Or at least dying of old age in bed, with weeping heirs all about. Not many sailors were so fortunate.

Jun 06, 2018
The problem with the study comes from another side - it shrinks the migration pause to ~ 3 kyrs. The dating of remains south of the ice barrier, of people who may have vanished from the genetic record, is fuzzy. But it looks good against the available data!

""The rock surfaces are smooth and scratched from when the ice moved over it, and there are erratic boulders everywhere. When you are a geologist, it hits you in the face."

I am no geologist, but even I can tell from that first photo as I live in a postglacial area. Lots of mountain and coastline looks like that around here.

Jun 06, 2018
By the way, there is firm evidence of people in the southwest of the U.S. 30,000 years ago. How did they get there? There are potentially even older dates for people in South America. Did they come across a land bridge from Antarctica? /s After all, the Piri Reis map shows an ice free continent, drawn before they had complete maps of North and South America.


By the way, there is not any firm evidence of that nature, and the one find that is possibly 30kyrs is contentious. But if any such finds would hold up, see my previous comment, the ice barrier era is now short.

The coastal migration pathway has been the mainstay of paleontology for decades by the way, read about it. It is lately that there has been finds that show some shortcuts in Levant and Asia (and possibly America, c.f. the still viable corridor and plausible genetic flow patterns further south).

[tbctd]

Jun 06, 2018
[ctd] The Piri Reis map is not the most accurate from those times, and the North American coastline especially unrealistic. "There is some suggestion that this area may represent the Asian coast."

"More recently, the map has been the focus of pseudohistoric claims for the pre-modern exploration of the Antarctic coast."

[ https://en.wikipe...Reis_map ]

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