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Why does the dating of the Cretaceous-Paleogene boundary have a margin of error?

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Cretaceous paleogeography — Cretaceous Period Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the late Cretaceous Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

The dating of the Cretaceous-Paleogene (K-Pg) boundary—formerly known as the K-T boundary—carries a margin of error because the precision with which geologic time can be measured is inherently limited, regardless of the methods employed, such as radiometric, paleomagnetic, or stratigraphic analysis.1

Even when utilizing the most advanced radiometric dating techniques, researchers face a margin of error on the order of 50,000 years when attempting to pinpoint this boundary. This uncertainty arises because radiometric dating relies on the accurate measurement of parent and daughter isotope ratios, which requires that the geologic sample has remained a closed system—meaning no parent or daughter atoms have been added or lost since the rock or mineral formed. Furthermore, any uncertainty in the measurement of these ratios contributes directly to the overall uncertainty of the calculated age.12

Because of these limitations, it remains difficult to determine whether the associated mass extinctions were instantaneous or occurred over a longer, nonsynchronous period. While rare, instantaneous geologic markers like the iridium anomaly associated with the Chicxulub impact provide significant reference points, yet they do not eliminate the fundamental challenges in achieving absolute temporal precision.13