The atmospheric ratio of carbon-14 to carbon-12 has not been constant over time — it has varied in response to solar activity, geomagnetic changes, and other factors.

These variations mean that a given radiocarbon age does not always correspond to the same calendar age.

The calibration curves — established by comparing radiocarbon measurements to independent chronological records, primarily tree rings — convert radiocarbon ages to calendar age ranges.

The stable isotope analysis that revealed Shuká Káa’s marine diet works on a different principle.

Carbon and nitrogen occur in nature as mixtures of different stable isotopes — variants of the same element with different numbers of neutrons.

The specific ratios of these isotopes in different food types reflect the specific biogeochemical processes that produce them.