Updating the Cambrian Time Scale: A Bayesian Approach Grunert, David de Vleeschouwer, Anna-Joy

Numerous fundamental events in the history of life on Earth took place during the Cambrian Period, including the Cambrian Explosion, the Cambrian Substrate Revolution, and onset of the Ordovician Planktonic Revolution. Despite the importance of these evolutionary milestones, determination of the timing and driving mechanisms of these events has been impeded by limited time constraints coupled with widespread endemism, leading to unclear biostratigraphic correlations among key localities. In the Geologic Time Scale 2020 (GTS2020), the time calibration of the Cambrian Period relies on 16 radioisotope ages. Information about age uncertainties is not included in GTS2020 or in the International Chronostratigraphic Chart v. 2024/12 (ICC 2024/12), with the exception of the Ediacaran/Cambrian and Cambrian/Ordovician boundaries. Since 2020, new radioisotope ages and cyclostratigraphic sections have been identified in the 542-485 Ma interval. Combined with the GTS2020 and modelled using the Bayesian “ModifiedBchron” R package, these data substantially refine the Cambrian Time Scale and provide continuous uncertainty estimates. This new Bayesian Time Scale provides ages and uncertainties for stage boundaries (and all points in-between) that closely align with the GTS2020 and ICC 2024/12 estimates. The new Cambrian Bayesian Time Scale not only identifies those stratigraphic intervals with limited or no numerical age constraints, it also enables to give a robust age for the carbon isotopes excursion, the Lagerstätten and in fine significantly improve the timing resolution of the key evolutionary events that took place during the Cambrian.