Conversely, in some geological contexts, older carbon can contaminate specimens and produce dates that are older than the actual age.

The researchers who produced the 2017 dates took precautions against contamination — standard pretreatment procedures were applied to remove potential contaminants — but the possibility of contamination cannot be entirely eliminated.

The stratigraphic context of the dated specimens is also important: if the specimens were not in their primary depositional context — if they had been moved from older deposits into younger ones by frost heaving, water movement, or carnivore activity — then the date of the specimen might not accurately reflect the age of the sediment context from which it was recovered.

These are legitimate methodological concerns that the authors acknowledged in their paper, and they represent the kind of ongoing scrutiny that any important archaeological claim should receive.