Radiocarbon Calibration

Radiocarbon calibration converts a laboratory radiocarbon measurement into a probability distribution over actual calendar years. It is necessary because the assumptions behind a raw radiocarbon age are not exactly true: the concentration of carbon-14 in the atmosphere has varied over time, so a measured radiocarbon age does not equal a calendar age. Calibration corrects for this by comparing the measurement against an internationally agreed curve — currently IntCal20 — that records the relationship between radiocarbon age and calendar age, reconstructed from precisely dated tree rings, corals, speleothems, and other archives. Because the curve wiggles, calibration typically yields an irregular, sometimes multi-peaked range of calendar years rather than a single date, and that range is the proper expression of a radiocarbon result.