The skepticism was not irrational.

Cinq-Mars was making an extraordinary claim — that humans had been in eastern Beringia during the coldest part of the Ice Age, more than 10,000 years before the Clovis culture, which was then the most widely accepted candidate for the first Americans.

Extraordinary claims require extraordinary evidence, and the extraordinary evidence was not universally convincing.

The specific concerns raised by critics of Cinq-Mars’s conclusions were both methodological and substantive.

On the methodological side, the stratigraphy of the cave sediments — the layering of deposits that is the primary means of establishing the relative age of archaeological materials — was complicated by natural processes of sediment mixing, frost heaving, and carnivore disturbance that could move older and newer materials into the same layer, making it difficult to be certain that objects from the same stratigraphic context were actually contemporaneous.