| Measurement of geological time is the key to understanding processes that occurred during the fascinating history of planet Earth. In particular the Paleogene (~65-23 million years ago) marks an intriguing period of time characterized by the transition from ?Greenhouse? to ?Icehouse? world, by extreme impacts and by transient warming events during which massive volumes of greenhouse gasses were abruptly injected into the atmosphere. Unfortunately, accurate measurement of geological time is a first order problem for earth scientists, leaving the Paleogene Time Scale still in a state of flux. Significant revisions are regularly published, preventing us from fully grasping Paleogene history. Here I propose to recalibrate this time scale in an international effort using in first instance the radio-isotopic 40Ar/39Ar and U/Pb techniques. I already improved the accuracy of the 40Ar/39Ar method by calibrating it to the astronomical tuned chronology for the late Neogene, resulting in much more accurate 40Ar/39Ar dates. This major achievement is a requirement for the logical next step of anchoring the astronomical tuning of cyclic Paleogene successions. It is anticipated that our intercalibration and recalibrated time scale will be incorporated in the next version of the standard Geological Time Scale, thereby avoiding the use of discrepant ages that result from the application of widely different dating techniques. Evidently a much improved Paleogene Time Scale is a prerequisite for unraveling the intriguing history of this crucial time interval. It can be directly applied to assess fundamental issues such as the potential influence of long-period orbital climate forcing which operates on million-year (tectonic) time scales. |
