Geoflex lezing: De Krijt-Paleogeen massa-extinctie: Laatste ontwikkelingen
Op 5 november zijn leden van de NGV uitgenodigd om een lezing bij te wonen van de studentenvereniging GeoVusie van de afdeling Aardwetenschappen Vrije Universiteit Amsterdam. De lezing is in het Engels kan bijgewoond worden via Zoom. De lezing wordt gegeven door Jan Smit en is getiteld: The KPg boundary mass-extinction: latest developments.
Andere geïnteresseerden kunnen een e-mail sturen naar Jan Smit, secretaris van de NGV om de inloginformatie te verkrijgen.
The end of the dinosaurs at the Cretaceous-Paleogene boundary (KPgB) has been subject for debate for over hundred years. Through the investigations of Walter Alvarez in Italy and me in Spain and at the UvA/VU, the possibility of a cosmic disaster became a likely hypothesis. The mode of extinction -extremely sudden- and the presence of anomalous iridium in a mm thin ejecta layer exactly at the KPgB pointed in the direction of a gigantic meteorite impact. In the decades following the discovery of iridium additional evidence, a.o. by my students at the VU, additional evidence piled up. Little spherules of impact glass (micro-tektites) and glass with quench crystals (micro-krystites) and shocked quartz in the mm thin ejecta layer. Tsunami sandstones around the Gulf of Mexico, cosmic Cr-isotope ratios all at the KPgB and, finally, the discovery of the Chicxulub crater, are now a very robust foundation for the impact extinction theory. A new scientific deep drill-hole in the crater itself (IODP exp364) has re-aligned all the separate discoveries.
Volcanism (Deccan traps), sometimes raised as an alternative cause for the mass-extinction, has -by far- not reached a similar status! One thing was lacking: the direct victims of the Chicxulub impact itself. Those victims have recently been found in North Dakota entombed in the mudstones left behind by a series of tsunami-seiche’s. The numerous finds in the mudstones are actually a snapshot of life on the continent and estuaries at the close of the Cretaceous. The victims died while the ejecta from the impact were still returning to the Earth’s surface. Impact glass is stuck in the gills of fishes while they were swimming in the river, and is caught in resin -now amber- made soft by impact-induced wildfires. The disappearance of a whole ecosystem dominated by dinosaurs has, with little doubt, led to the explosive evolution of modern mammal species. We, mankind, are the descendants of these species.