Crag Cave and Castlepook
At this depth of time, the distinction between radiocarbon years and calendar years is essential. Radiocarbon dates measure the remaining carbon-14 in once-living material; because atmospheric carbon-14 has varied, laboratory results must be calibrated against independently dated records. IntCal20, the current Northern Hemisphere calibration curve, extends to 55,000 calibrated years before present, but uncertainty becomes substantial in this remote period. A date such as 30,830 BCE should therefore be treated as a modern filing label, not as an ancient date known to its inhabitants.