In the 1930s, archaeologists discovered “Clovis culture” spearheads on the Great Plains. These hunting tools have been found alongside the remains of mastodons, mammoths and several extinct bison species. The dots have been dated to around 11,000 years old, making them the oldest fossil evidence of settlement in North America ever discovered at that time. It was an exciting discovery, which reignited the debate about the migration patterns of early humans.
The question of when and how ancient humans arrived in the Americas is one of the greatest and most enduring mysteries of early human migration – all for the simple reason that North and South America separated from the other continents more than 80 million years ago. In the 16th century, a Spanish Jesuit scholar named Fray Jose de Acosta theorized that the ancestors of today’s Native Americans crossed into Asia on dry lands that had since been submerged.
Future generations of scholars adopted De Acosta’s belief that early American settlers traveled on foot and designated Beringia – a land bridge that once connected Alaska to northeast Asia – as their point of departure. most likely entry. This otherwise compelling story had a major plot hole: for much of the Late Pleistocene epoch, western Canada was covered by the Laurentian and Cordilleran ice sheets, which would have blocked access in the Great Plains.
To circumvent this plot, archaeologists like WA Johnson and Mary Wormington developed the bold but seemingly incontrovertible hypothesis that early humans hunted their megafauna prey through an “ice-free corridor” that briefly formed between the ice sheets and stretched across Alberta and British Columbia. British to today’s United States. This, the academic community agreed, was the most likely explanation for the spearheads of the Clovis culture.
The “Clovis first” hypothesis, as this idea is sometimes called, has long dominated discussions of early human migrations to the Americas. Although many new research projects – from advances in our understanding of glaciology and plate tectonics to recent discoveries of even older fossils in parts of Central and South America – have challenged this assumption, it has never been successfully debunked. That is, until now.
Put a hypothesis to rest
The reason researchers took more than 60 years to verify if the ice-free corridor was used by ancient humans is that for most of that time they didn’t have the knowledge to do so. As Lional Jackson and Michael Wilson stated in their literature reviewattempts to verify Clovis First’s theory “relyed on recently developed analytical techniques, including radiocarbon and cosmogenic exposure dating”.
A article published in 2016 by Cambridge University Press aggregated radiocarbon dating of the ice-free corridor from earlier archaeological, geological, and palynological studies to determine that “the corridor was not feasible as an early route before 11,000 BP, or after the appearance of Clovis south of the glaciers continentals”. This article confirmed widespread suspicions that the corridor was too inhospitable for early humans to have passed through.
Another study, published by the Proceedings of the National Academy of Sciences last March provided even more compelling evidence that the Clovis First hypothesis was incorrect. A team of researchers led by Jorie Clark, a professor at Oregon State University, calculated the age of 64 rock samples taken from Alberta and British Columbia, the same region where the Laurentide and Cordillera ice sheets are thought to have split.
“We used a method known as cosmogenic nuclide exposure dating,” explained Louise Guillaume, a graduate student in geology from Imperial College London who contributed to the lab work. press release published on the school website. Cosmogenic exposure dating” is a “rock clock” that basically tells us how long rocks have remained exposed on the Earth’s surface – after a glacier has retreated and left them behind and uncovered, for example”.
Using this rock clock, Clark’s team was able to date the opening of the ice-free corridor to around 13.8 thousand years ago, roughly 500 years old. Even with this graceful margin of error, the study proves that the corridor only opened up after North America was already populated. “We’ve closed the door on the ice-free hallway,” study co-author Dylan Rood announced in the aforementioned press release, adding that they’ve successfully put “the Clovis First theory to rest.” “.
The ice-free corridor opened “like a zipper”
Although the study indicates that parts of the ice-free corridor opened up 15,000 years ago, the corridor as a whole did not become ice-free until long after people arrived in the Western Hemisphere. Clark told Imperial College London that the corridor opening was “like a zipper” and that this zipper was “opened first from below”, starting from the south and “then decompressed from above”.
There are other studies that argue that the Clovis First hypothesis was incorrect. In recent decades, archaeologists in South America have uncovered evidence of human settlement on the continent that is much, much older than Clovis points. Bone, charcoal, and sediment samples recovered from Chiquihuite Cave in north-central Mexico by the Autonomous University of Zacatecas in 2012for example, have been dated to 26,000 years old, but can be as old as 33,000 years old.
Chiquihuite Cave joins half a dozen other excavations in Central and South America that predate the opening of the ice-free corridor. Equally ancient remains have been found in the Andes, the Amazon basin, the Patagonian steppe in Argentina and on the Caribbean coast. “On the evidence of these earliest archaeological sites from over 13,000 years ago”, yet another review of the literature echoes“the Clovis-first model must be abandoned.”
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Of course, abandoning the Clovis First model means that researchers must once again face the daunting question of when and how ancient humans arrived in the Western Hemisphere. As popular support for one hypothesis declines, interest in another increases. Clark’s article leans in favor of the Pacific Coast Migration, or Kelp Highway, model, which proposes that early American settlers traveled along the Pacific coast rather than through the heartland of Canada.
Due to rising sea levels, the coastline along which these primordial pioneers may have originally traveled is well beyond current archaeological reach. Yet excavations from different parts of the world – including evidence of shipping in greater Australia, which may have been settled by people using watercraft 50,000 years ago – to make the Pacific coast migration model appear as likely, if not more so, than the Clovis First hypothesis.