Alaska’s Pacific coast may have been ice-free 17,000 years ago allowing early settlers to reach North America from Eurasia, ancient boulders reveal

  • Conventional theory suggests that the earliest settlers came via Siberia
  • However, scientists now believe the first Americans took a coastal route
  • Discovery was made after studying boulders, bedrock and fossils in Alaska
  • The area was also home to food sources such as ancient ringed seal that could support human life at the time 
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How early humans first got to the Americas has long been debated by scientists.

The conventional story goes that the earliest settlers came via Siberia, crossing the now-defunct Bering land bridge on foot and trekking through Canada. 

However, some scientists believe the first Americans may have taken a coastal route along Alaska’s Pacific border to enter the continent.

Now, a new study has come up with some of the first evidence to support this theory by looking at boulders and bedrock in the region.

Researchers say they have ‘direct evidence’ that part of a coastal migration route was ice-free and accessible to humans 17,000 years ago.

The area was also home to food sources such as ancient ringed seal that could support human life at the time that early settlers may have been passing through, the study found.

Researchers aren’t saying humans definitely travelled along this coastal route, but claim conditions would have been right for them to do so 17,000 years ago.

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The conventional story says that the earliest settlers came via Siberia, crossing the now-defunct Bering land bridge on foot and trekking through Canada. Scientists now believe the first Americans could have taken a coastal route along Alaska’s Pacific border to enter the continent


By analysing boulders and bedrock (pictured), researchers say they have ‘direct evidence’ that part of a coastal migration route became accessible to humans 17,000 years ago

‘Our study provides some of the first geologic evidence that a coastal migration route was available for early humans as they colonised the New World,’ said University at Buffalo geology PhD 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.’.

The findings, published in the journal Science Advances, suggest that Alaska’s southern coast route into the Americas is viable.

‘We’re not definitively saying they took the coastal route,’ Ms Lesnek told New York Times.

‘We have some of the first direct evidence that that was something that could be done’, she said.

Researchers had previously found bones of an ancient ringed seal in a nearby cave that were about 17,000 years old.

This indicates that the region was ecologically vibrant soon after the ice retreated, with resources including food becoming available. 


Scientists now believe the first Americans took a coastal route along Alaska’s Pacific border to enter the continent (pictured). Scientists travelled to four islands within Alexander Archipelago that lie about 200 miles (320km) south of Juneau


During this period, ancient glaciers receded, exposing islands of southern Alaska’s Alexander (pictured). The area was home to food sources such as ancient ringed seal that could support human life at the time that early settlers may have been passing through, the study found 

HOW DID OUR ANCESTORS FIRST REACH 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. 

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.

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.

Scientists now believe the first Americans could have taken a coastal route along Alaska’s Pacific border to enter the continent.

This theory provides an alternative narrative and could mark a step toward solving the mystery of how humans came to the Americas.

By analysing boulders and bedrock, researchers from the University at Buffalo say they have ‘direct evidence’ that part of a coastal migration route along Alaska’s Pacific became accessible to humans 17,000 years ago.

During this period, ancient glaciers receded, exposing islands of southern Alaska’s Alexander.

The area was home to food sources such as ancient ringed seal that could support human life at the time that early settlers may have been passing through.

Recent genetic and archaeological estimates suggest that settlers may have begun travelling deeper into the Americas some 16,000 years ago, soon after the coastal gateway opened up.

‘Our research contributes to the debate about how humans came to the Americas’, said lead scientist Jason Briner, PhD, professor of geology in University at Buffalo’s College of Arts and Sciences. 

‘It’s potentially adding to what we know about our ancestry and how we colonised our planet’, he said.  

Scientists travelled to four islands within Alexander Archipelago that lie about 200 miles (320km) south of Juneau.

To pinpoint when the ice receded from the region, the team collected bits of rock from the surfaces of boulders and bedrock.

Later, they ran tests to figure out how long the samples – and thus the islands as a whole – had been free of ice.


Researchers had previously found bones of an ancient ringed seal in a nearby cave that were 17,000 years old. PhD candidate Alia Lesnek (pictured) works at Suemez Island


To pinpoint when the ice receded from the region, the team collected bits of rock from the surfaces of boulders and bedrock


Pictured is Dr Jason Briner collecting a rock sample on Suemez Island. Researchers ran tests to figure out how long the samples – and thus the islands as a whole – had been free of ice

They used a method called surface exposure dating.

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, causing it to accumulate certain chemicals on their surface.

‘The longer the surface has been exposed, the more of these chemicals you get’, said Ms Lesnek.

‘By testing for these chemicals, we were able to determine when our rock surfaces were exposed, which tells us when the ice retreated’, she said. 

Researchers used this method on huge boulders called erratics.


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, causing it to accumulate certain chemicals on their surface


Pictured are researchers at Baker Island. In recent years, evidence has mounted against the conventional thinking that humans populated North America by taking an inland route through Canada

‘These are big rocks that are plucked from the Earth and carried to new locations by glaciers, which actually consist of moving ice’, said Ms Lesnek.

‘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.

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.


To collect data, the research team travelled by helicopter to remote sites within the Alexander Archipelago in southeast Alaska


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


Researchers, including team members from the University at Buffalo and the US Forest Service (pictured), travelled by boat to Warren Island, one of the study sites

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.

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,’ said Dr Charlotte Lindqvist, an associate professor of biological sciences at University at Buffalo. 

‘The timing coincides almost exactly with the time in human history that the migration into the Americas is thought to have occurred’, she said. 

WHAT DO WE KNOW ABOUT OUR ANCESTORS?

Four major studies in recent times have changed the way we view our  ancestral history.

The Simons Genome Diversity Project study

After analysing DNA from 142 populations around the world, the researchers conclude that all modern humans living today can trace their ancestry back to a single group that emerged in Africa 200,000 years ago.

They also found that all non-Africans appear to be descended from a single group that split from the ancestors of African hunter gatherers around 130,000 years ago.

The study also shows how humans appear to have formed isolated groups within Africa with populations on the continent separating from each other.

The KhoeSan in south Africa for example separated from the Yoruba in Nigeria around 87,000 years ago while the Mbuti split from the Yoruba 56,000 years ago.

The Estonian Biocentre Human Genome Diversity Panel study

This examined 483 genomes from 148 populations around the world to examine the expansion of Homo sapiens out of Africa.

They found that indigenous populations in modern Papua New Guinea owe two percent of their genomes to a now extinct group of Homo sapiens.

This suggests there was a distinct wave of human migration out of Africa around 120,000 years ago.

The Aboriginal Australian study

Using genomes from 83 Aboriginal Australians and 25 Papuans from New Guinea, this study examined the genetic origins of these early Pacific populations.

These groups are thought to have descended from some of the first humans to have left Africa and has raised questions about whether their ancestors were from an earlier wave of migration than the rest of Eurasia.

The new study found that the ancestors of modern Aboriginal Australians and Papuans split from Europeans and Asians around 58,000 years ago following a single migration out of Africa.

These two populations themselves later diverged around 37,000 years ago, long before the physical separation of Australia and New Guinea some 10,000 years ago.

The Climate Modelling study

Researchers from the University of Hawaii at Mānoa used one of the first integrated climate-human migration computer models to re-create the spread of Homo sapiens over the past 125,000 years.

The model simulates ice-ages, abrupt climate change and captures the arrival times of Homo sapiens in the Eastern Mediterranean, Arabian Peninsula, Southern China, and Australia in close agreement with paleoclimate reconstructions and fossil and archaeological evidence.

The found that it appears modern humans first left Africa 100,000 years ago in a series of slow-paced migration waves.

They estimate that Homo sapiens first arrived in southern Europe around 80,000-90,000 years ago, far earlier than previously believed.

The results challenge traditional models that suggest there was a single exodus out of Africa around 60,000 years ago.

 

 

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