GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 95-9
Presentation Time: 10:25 AM


KELLER, Gerta, Department of Geosciences, Princeton University, Guyot Hall, Princeton, NJ 08544

The Cretaceous–Paleogene boundary (KPB) mass extinction (66 Ma) is primarily known for the demise of dinosaurs, the Chicxulub impact, and the rancorous forty-years-old controversy over the cause of this mass extinction. The impact hypothesis proposed by Alvarez and others in 1980 based on an Iridium anomaly in a thin clay layer coincident with the mass extinction was declared a proven theory by the authors within less than 2 years and without testing evidence. The popular appeal cemented the impact theory as “truth”, most scientists became believers and contrary evidence was dismissed or ignored. Scientists who questioned the theory, revealed contrary evidence and proposed alternative causes were confronted with mass hostility, public ridicule, character assassination, prevention of publishing results and threats of destroying their careers. This tactic succeeded to silence almost all within just a few years and destroyed careers of the most prominent early opponents of the impact theory leaving just one and a small team to amass evidence and battle vicious attacks for the past three decades. In a perverse twist of fate, the 1990 discovery of the Chicxulub crater began the decline of the impact theory because for the first time it could be tested directly based on the impact crater and surrounding impact glass spherule ejecta. Multiple sources of evidence revealed the Chicxulub impact predated the KPB by ~190 ky based on the primary impact spherule layer in NE Mexico and impact breccia in the Chicxulub crater separated from the KPB mass extinction by laminated late Maastrichtian sediments in four separate impact crater drillings. This evidence was dismissed based on the impact generated tsunami scenario that lacked evidence but assumed deposition between impact breccia and KPB was deposited within hours to days thus proving the impact’s KPB age. Irrefutable evidence of massive Deccan volcanism in India culminating with the largest eruption phase at the KPB mass extinction was recently interpreted as triggered by the impact - another scenario lacking any evidence. This talk highlights the accumulated evidence that disproves the impact theory and supports Large Igneous Province (LIP) volcanism as the most likely cause for the KPB and other Phanerozoic mass extinctions.