Cretaceous–Paleogene extinction event

Cretaceous–Paleogene extinction event
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Name	Cretaceous–Paleogene extinction event
Time	~66 million years ago
Period	Cretaceous, Paleogene
Primary causes	Chicxulub impact, Deccan Traps volcanism
Major losses	Non-avian Dinosaurs, many Ammonites, marine reptiles
Notable sites	Chicxulub crater, Hell Creek Formation, Deccan Traps, Raton Basin

Cretaceous–Paleogene extinction event was a major biotic crisis about 66 million years ago that ended the Cretaceous and initiated the Paleogene. It produced rapid, global losses of taxa including non-avian Dinosaurs, many Ammonite lineages, and numerous marine and terrestrial groups, reshaping ecosystems and enabling the diversification of Mammalia, Aves, and Angiosperm-dominated floras. The event links to geological features such as the Chicxulub impact structure, the Deccan Traps flood basalts, and stratigraphic records like the Hell Creek Formation and Raton Basin sections.

Background and timing

The event marks the Cretaceous–Paleogene boundary recorded in stratigraphic sequences worldwide, often identified by a thin clay layer enriched in Iridium and coincident with shocked Quartz and spherules at localities including the Hell Creek Formation, Raton Basin, and sites studied by teams from institutions such as the Smithsonian Institution and the Natural History Museum, London. Radiometric dating of the Chicxulub impact structure, analyses by researchers affiliated with the University of California, Berkeley and the Geological Survey of Canada, and magnetostratigraphic correlations tie the extinction to a narrow interval near the Maastrichtian–Danian transition recognized in the Geological Time Scale used by organizations like the International Commission on Stratigraphy.

Causes and mechanisms

Competing and complementary hypotheses include the bolide impact hypothesis centered on the Chicxulub crater offshore of the Yucatán Peninsula, advanced in work by teams from the University of Arizona and proponents linked to the discovery by researchers associated with the Geological Society of America, and the volcanism hypothesis emphasizing the timing and magnitude of the Deccan Traps eruptions studied by investigators at the Indian Statistical Institute and universities such as Pune University. Mechanistic pathways invoked involve abrupt atmospheric aerosol loading and planetary darkness from ejecta and soot as modeled by groups at the National Center for Atmospheric Research and the Jet Propulsion Laboratory, acid rain and ocean acidification effects evaluated by labs at the Scripps Institution of Oceanography and Woods Hole Oceanographic Institution, and longer-term climate forcing and greenhouse gas inputs tied to basaltic effusions analyzed by teams at the Lamont–Doherty Earth Observatory and the Max Planck Institute for Chemistry. Recent syntheses from consortia including members of the Royal Society and the National Academy of Sciences argue for a multi-causal scenario linking impact and volcanism.

Extent and patterns of extinction

Extinction patterns show selectivity across taxa: non-avian Dinosaur clades such as ceratopsians and hadrosaurids vanish from latest Cretaceous assemblages in formations like Hell Creek studied by paleontologists associated with the American Museum of Natural History and universities such as Montana State University, while avian lineages within Aves persist. Marine planktonic groups including foraminifera and calcareous nannoplankton suffer major turnovers documented in cores from the Ocean Drilling Program and the Integrated Ocean Drilling Program, and reef-building organisms decline in records analyzed by researchers at the Smithsonian Tropical Research Institute and the University of Queensland. Biogeographic patterns reconstructed by teams at the University of Cambridge and the University of São Paulo show differential extinction severity across provinces documented in European, North American, Asian, and Gondwanan localities.

Immediate environmental effects

Short-term environmental consequences inferred from geochemical and sedimentary proxies include global darkness, cooling, and subsequent warming phases recorded in isotopic datasets from laboratories at the Massachusetts Institute of Technology and the University of Copenhagen, widespread wildfires inferred from charcoal layers examined by investigators at the University of Colorado Boulder and the University of Tokyo, and rapid ocean acidification and anoxia traced by carbonate dissolution indicators studied by researchers at the University of Oxford and the University of Edinburgh. Atmospheric sulfate and CO2 perturbations modeled by groups at the Pacific Northwest National Laboratory and the Lawrence Livermore National Laboratory help explain marine extinctions and terrestrial plant and vertebrate crises preserved in continental basins such as the Raton Basin and the North American Hell Creek exposures.

Recovery and aftermath

Post-extinction ecosystems show rapid evolutionary radiations among surviving clades: Mammalia diversify into niches vacated by extinct megafauna, with paleontological evidence from Paleocene sites like the Paleocene–Eocene Thermal Maximum studied by teams at the Field Museum and the New York Botanical Garden. Angiosperm-dominated floras rebound and restructure terrestrial habitats in records curated by the Royal Botanic Gardens, Kew and the Missouri Botanical Garden. Marine ecosystems recover through successive turnovers documented in ODP cores analyzed by scientists at the University of Bremen and the University of Tasmania, while adaptive radiations in groups such as modern Sharks, Teleostei fishes, and crown-group Aves are inferred from fossil lineages chronicled by researchers at the Natural History Museum of Los Angeles County and the Canadian Museum of Nature.

Evidence and key discoveries

Key pieces of evidence include the global iridium anomaly first noted by researchers associated with institutions like the University of California, Berkeley and the Geological Survey of Canada, the identification of shocked minerals and spherules at K–Pg sites examined by teams from the University of New Mexico and the Massachusetts Institute of Technology, and the mapping and drilling of the Chicxulub structure led by groups from the United States Geological Survey and the National Autonomous University of Mexico (UNAM). Landmark fossil localities such as the Hell Creek Formation, studied by paleontologists at the Burke Museum and the Museo del Desierto, provide detailed faunal turnover records, while geochronological advances from labs at the California Institute of Technology and the Swiss Federal Institute of Technology (ETH Zurich) have refined the timing. Interdisciplinary syntheses by committees under the aegis of the National Academies and international collaborations across universities including Yale University, Columbia University, and the University of Tokyo continue to integrate stratigraphic, geochemical, palaeontological, and modeling evidence to resolve remaining questions.

Category:Mass extinctions