The Chicxulub File: Discovering the K-Pg Mass Extinction A Four Decade Perspective

Abstract

In 1979 geologists Luis and Walter Alvarez discovered a layer of iridium-rich rock in the Apennine Mountains dating from 66 to 65 million years BP, the time when dinosaurs went extinct. Their theory that an asteroid strike had caused this massive extinction remained speculative and controversial until the 1991 discovery of a telltale crater from a synchronous asteroid impact. The effects of this impact, centered at Chicxulub on the Yucatan Peninsula, were worldwide. Over the years, impact spherules were found at numerous sites, along with evidence of a massive tsunami throughout the Gulf of Mexico and adjacent coasts. From accumulating evidence, the theory was ratified in 2012, though many details remained unknown. However, a series of dramatic discoveries reported from 2019 to 2022 have led to a chronology of events both during and subsequent to the impact. Evidence for the rapid recovery and development of mammals has been found in the fossil record and, thus, the biological foundations of our own emergence. The final 2019 issue of Science (20 December) named this a “superyear” for studies of the Cretaceous-Paleogene (K-Pg) extinction as the runner-up science “breakthrough of the year.” Through these separate discoveries, a coherent hour-by-hour narrative has emerged, marking the onset of the Cenozoic era and providing a foundation for the emergence of Homo sapiens.