AMS dating worked differently: it directly counted the individual carbon-14 atoms in a sample, using a particle accelerator to separate them from the more abundant stable carbon isotopes.

This approach required far smaller samples — sometimes only a few milligrams of material — and was considerably more precise, with smaller uncertainty ranges on the resulting dates.

Crucially, AMS dating could be applied directly to the collagen extracted from bone, rather than requiring larger bulk samples.

Bone collagen, when it has survived intact, provides one of the most reliable organic materials for radiocarbon dating — it is less susceptible to the contamination that can affect charcoal or bulk organic sediment.

The team assembled by Michael Waters of Texas A&M University — a specialist in the geology and dating of early American sites and one of the leading investigators of pre-Clovis evidence — resampled the Manis mastodon material using AMS methods.