Accelerator mass spectrometry, or AMS dating, allows researchers to measure carbon-14 directly on very small samples — often just a few milligrams of material — with high precision.

The dates obtained from Buckeye Knoll were not based on a single sample from a single individual.

They were produced from multiple individuals, using multiple samples, generating a distribution of dates that collectively span from approximately 8,500 before present to approximately 500 before present.

The oldest dates, from tooth and bone collagen samples from the earliest burials, consistently place those individuals in the early Holocene — the geological epoch that began approximately 11,700 years ago when the last great ice sheets were in final retreat.

Calibration matters here.