K–Pg extinction event

K–Pg extinction event
Name	K–Pg extinction event
Time	Cretaceous–Paleogene boundary, ~66 Ma
Location	Global
Cause	Chicxulub impact, Deccan Traps volcanism (debated)
Severity	Mass extinction

Contents

K–Pg extinction event The K–Pg extinction event marks a major biotic turnover at the end of the Cretaceous and start of the Paleogene, approximately 66 million years ago. It abruptly eliminated numerous Tyrannosaurus, Triceratops, Pterosauria, Mosasaurs, Ammonites, and many other distinctive Cretaceous clades, while enabling the radiation of Mammalia, Aves, Angiosperms, and modern Teleostei. The event is central to studies by institutions such as the Smithsonian Institution, Natural History Museum, London, American Museum of Natural History, and research programs at Caltech, MIT, and the University of Colorado Boulder.

Overview and timing

Radiometric dating of ejecta layers and stratigraphic correlations using sites like the Gubbio sections, the El Kef boundary, and the Chicxulub crater yields an age near 66.0 Ma with resolution from laboratories at ETH Zurich, University of California, Berkeley, Rice University, and Scripps Institution of Oceanography. High-precision analyses by teams associated with Woods Hole Oceanographic Institution, University of Oslo, University of Buenos Aires, and Universidad Nacional Autónoma de México integrate magnetostratigraphy, biostratigraphy using Foraminifera and Diatoms, and chemostratigraphy employed by researchers at Geological Survey of Canada and the United States Geological Survey.

The primary causal hypotheses involve the Chicxulub bolide impact documented by geologists from University of Texas at Austin, Universidad Nacional Autónoma de México, Imperial College London, and Vrije Universiteit Amsterdam, and contemporaneous flood basalt volcanism from the Deccan Traps studied by teams at University of Cambridge, Indian Institute of Science, University of Toronto, and Purdue University. Mechanistic models developed by groups at NASA, European Space Agency, Max Planck Society, and Los Alamos National Laboratory simulate atmospheric loading, ejecta injection, global firestorms, acid rain, aerosol-induced sunlight reduction, and oceanic anoxia. Climate modelers at Princeton University, University of Oxford, Columbia University, and University of Chicago examine combined impact-volcanism scenarios, while paleontologists at National Museum of Natural History (France), Royal Ontario Museum, and Field Museum assess biotic responses.

Marine losses include extinction of Ammonites, many Belemnites, pelagic Foraminifera, and nektonic reptiles such as Mosasaurs and Plesiosaurs, documented by curators at Natural History Museum of Los Angeles County, Royal Belgian Institute of Natural Sciences, and Museo Argentino de Ciencias Naturales. Terrestrial extinctions encompass non-avian Dinosauria like Hadrosaurus and Ceratopsia, pterosaurs documented by researchers at University of Bristol and University of Kansas, and many plant groups recorded by palynologists at Universität Wien and University of São Paulo. Survivors and radiations include Mammalia groups studied at Harvard University and Yale University, early Aves lineages examined by teams at University of Cambridge and Smithsonian National Museum of Natural History, and angiosperm survivors investigated by botanists at Royal Botanic Gardens, Kew and Missouri Botanical Garden.

Key geological evidence includes the iridium anomaly first reported by researchers affiliated with University of California, Berkeley, the discovery of shocked quartz and spherules by teams at University of Copenhagen and University of Kansas, and the identification of the Chicxulub crater by geophysicists from University of Arizona and GeoScience Australia. Geochemical proxies—stable isotopes, osmium excursions, mercury spikes, and clay mineral analyses—are produced by laboratories at Stanford University, University of Leeds, ETH Zurich, University of Rennes, and CSIC. Drill cores from the IODP and ODP programs, with contributions from Lamont–Doherty Earth Observatory, GEOMAR, and British Geological Survey, provide stratigraphic sequences of ejecta, tsunami deposits, and basal Paleogene sediments.

Post-extinction recovery dynamics, studied by paleontologists at University College London, University of Michigan, University of Texas at Austin, and University of Vienna, show staged rebounds in marine ecosystems with early Paleogene radiations of Foraminifera and Bivalvia, and terrestrial diversification of Mammalia, Rodentia, Primates, and Ungulates. Floral turnovers analyzed by researchers at University of Göttingen, University of Helsinki, and University of Alberta indicate angiosperm-dominated forests replacing many Cretaceous gymnosperm assemblages. Long-term climatic and oceanographic consequences are modeled by groups at NOAA, Met Office Hadley Centre, National Center for Atmospheric Research, and Swiss Federal Institute of Technology in Zurich.

The impact hypothesis, first championed by proponents linked to University of California, Berkeley and University of Arizona, generated debate with volcanism advocates from Indian Institute of Science and University of Delhi; subsequent collaborative work by teams at Caltech, MIT, University of Chicago, and Imperial College London has refined integrated scenarios. Ongoing controversies addressed at conferences hosted by International Geological Congress, Society of Vertebrate Paleontology, American Geophysical Union, and journals supported by Nature Publishing Group and Elsevier concern the relative timing of Deccan eruptions, the role of climate feedbacks, and selectivity patterns explored by researchers at Duke University, University of Zurich, McGill University, and Australian National University.

Category:Mass extinctions