Origin: A Genetic History of the Americas

10,000 years; unusual for rockshelters in the area, but not
unknown. Below the Archaic strata was a layer of rock—called
breakdown by cavers—from an event in which the shelter’s
ceiling had collapsed. Below that, in layers that were ultimately
dated to before Clovis, was clear evidence of human activities,
including a bifacially flaked spearpoint.
As Adovasio described in his book The First Americans, after
finding the point, “we immediately decamped to our favorite bar
in town and polished off ten kegs of beer.” He and the students
knew they had found something significant in the unpretentious
rockshelter. What they perhaps didn’t appreciate at the time is
how much of an uproar the find would ultimately cause.
The layers he and his students dug—properly termed
Stratum IIa—would go on to yield the remains of plants,
animals, and lithics that were ultimately dated to as old as
16,000 years ago, some 3,000 to 4,000 years earlier than the
then-known earliest date for Clovis. vi “Damn” was Adovasio’s
response as he stared at the report from the dating lab. He
believed in the evidence.
This was a paradigm-shattering find, but only if it held up to
the scrutiny of other archaeologists. And he knew the coming
scrutiny would be blistering.
There was nothing ambiguous about human activities
associated with Stratum Iia: this layer yielded dozens of stone
tools, including the projectile point, small blades, and unifacial
choppers and scrapers, made from raw materials brought to the
site from distant places.
Adovasio and his students had excavated the site so
meticulously that even the most vocal critics of the site could not
find fault with their methods or the stratigraphy. Rather, the
problem was with the dates themselves. They were too old,
critics argued. The dates had been confirmed by multiple
laboratories, including the outstanding lab at the Smithsonian,
so the issue must be contamination, some (like my own
professor) argued. Most likely the contamination was from the