The age of the opening of the Ice-Free Corridor and implications for the peopling of the Americas
Jorie Clark cs 2022 PNAS 119 (14) e2118558119
doi org/10.1073/pnas.2118558119

The Clovis-first model for the peopling of the Americas by ∼13.4 ka has long invoked the "IFC" between the retreating margins of the Cordilleran & Laurentide ice-sheets as the migration-route from Alaska & the Yukon, down to the Great Plains.
But evidence from archaeology & ancient genomics now suggests:
pre-Clovis migrations occurred by at least ∼15.5-16 ka, earlier than most recent assessments of the age of IFC opening at ∼14-15 ka,
this lends support to the use of a Pacific coast migration route instead.
But uncertainties in ages from the IFC used in these assessments allow for an earlier IFC opening, cons.x the availability of the IFC as a migration route by ∼15.5-16 ka?
Here we use 64 cosmogenic (10Be) exposure ages, to closely date the age of the full opening of the IFC at 13.8 ka ± 0.5:
the IFC was not available for the first peopling of the Americas after the Last Glacial Max.
Extensive geo-chronological data from the Pacific coast support its earlier availability as a coastal migration route.

Significance

The IFC has long played a key role in hypotheses about the peopling of the Americas.
Earlier assessments of its age suggested: the IFC was available for a Clovis-first migration,
but subsequent developments now suggest a pre-Clovis occupation of the Americas, before the opening of the IFC,
this supports a Pacific coastal migration route,
but large uncertainties in existing IFC ages cannot preclude its availability as a route for the first migrations. ...
We report cosmogenic nuclide exposure ages:
the final opening of the IFC occurred well after pre-Clovis occupation.

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littor...@gmail.com wrote:

Significance

The IFC has long played a key role in hypotheses about the peopling of the Americas.
Earlier assessments of its age suggested: the IFC was available for a Clovis-first migration,
but subsequent developments now suggest a pre-Clovis occupation of the Americas, before the opening of the IFC,
this supports a Pacific coastal migration route,
but large uncertainties in existing IFC ages cannot preclude its availability as a route for the first migrations. ...
We report cosmogenic nuclide exposure ages:
the final opening of the IFC occurred well after pre-Clovis occupation.

"Pre Clovis" is a fact now. NOBODY subscribes to "Clovis First." I don't even think the Out of Africa purists -- the bird brains who got a cracker every time they regurgitated what the professor told them, verbatim -- couldn't believe the "Clovis First" thing.

My long, Long, LONG argued model is that Clovis "Culture" makes a threshold. No, not when people got here, but when a population threshold was crossed
and "A culture" could span a very wide area.

People also had to adapt. Groups that arrived along the coast had to push inland, adapt to a new lifestyle & spread... exactly like we see happening all the way back to the miocene:

Waterside ("Aquatic Ape"). Pushing inland. Adapting.

It didn't stop with the Rift Valley or the Neanderthals/Denisovans or EVER.
The same process: Nature was always nature.






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