FROM 1979 TO 2021-OVER 40 YEARS OF EVOLUTION OF THE CRETACEOUS-TERTIARY IMPACT-EXTINCTION THEORY : FROM A SPECULATIVE HYPOTHESIS TO PARADIGM?

The quest for the ultimate cause of the extinction of the dinosaurs and about 72% of other species, remains one of the major detective stories in the history of our planet. Starting with the realization that the sudden, unannounced, Cretaceous-Paleogene (KPg) mass-extinction of marine calcareous plankton could not be explained by a hiatus in time, followed by the finding of anomalous iridium precisely at the moment of their disappearance reduced the whodunits to an extraterrestrial cause. Although further findings over the last 40 years increasingly confirmed a large impact event, culminating with the discovery of the Chicxulub crater, the opposition against the theory remained strong and active. At the same time, each new interpretation of the KPg geological record or a new discovery has repeatedly thrown us a number of curve balls. Diagenesis, poor outcrops, drilling disturbances, etc. has led to faulty interpretations, and often masked the true nature of these discoveries. E.g. it took a while to realize that the finely crystallized ‘sanidine’ and quenched magnesioferrite spinel-bearing spherules (microkrystites) were not compatible with an oceanic impact site, but rather with the composition of the Chicxulub crater target rocks. The coincidence of the Deccan trap outpourings and the Chicxulub impact has further fueled the debate. The present debate centers around the interpretation of the extinction record and the environmental proxies for climate change. Do these support an extended extinction, compatible with the Deccan traps, or is this record just "white noise" around the major extinction precisely at the iridium anomaly? In the struggle to support their mutual claims dirty -almost courtroom- tricks, i.e. on the edge of scientific correctness were used on either side to highlight the salient points. The public, -or rather the press- does not have the means to separate the chaff from the wheat, so scanning through newspaper clippings, both sides were mostly just given equal weight and recognition. Yet the unabated opposition also forced the proponents of the impact-extinction theory to have a second look at their data, that often cleaned the datasets. The recent Tanis, North Dakota, findings and IODP Exp364 drilling results in the crater itself have helped to raise the impact-extinction theory to the next level, perhaps to a new paradigm?