Radiocarbon dates are not the same as calendar dates, because the production of carbon-14 in the atmosphere has not been constant over time.

The atmospheric production rate varies with solar activity and other factors.

To convert a radiocarbon date into a calendar year, scientists use calibration curves derived from independently dated materials — primarily tree rings, which can be counted precisely and whose carbon content can be measured year by year going back thousands of years.

The calibrated dates for the earliest Buckeye Knoll burials place them at approximately 8,500 calendar years before present — that is, approximately 6,500 years before the common era.

To put this in human terms: these individuals were buried approximately 2,000 years before Stonehenge was built in England, roughly 1,500 years before the first Egyptian pyramids rose from the Nile Valley.