They have varied in response to changes in solar activity, geomagnetic field strength, and other factors.

A raw radiocarbon measurement — expressed as “radiocarbon years before present” — must be converted to calendar years using a calibration curve derived from independent records of past atmospheric carbon-14 concentrations.

For the MA-1 burial, the calibrated date of approximately 24,000 calendar years before present represents the result after applying this calibration.

The calibration curves for this time period are based on records from tree rings (for the recent portion of the calibration range), coral, and cave formations, and they carry some uncertainty, which is reflected in the error range typically reported with any ancient date.

The approximately 24,000-year figure is well-established within the expected uncertainties of the method.