Cretaceous–Paleogene

Cretaceous–Paleogene
Name	Cretaceous–Paleogene
Other names	K–Pg
Time start	66.0
Time end	66.0
Time uncertainty	0.05
Epoch	Maastrichtian–Danian boundary
Description	Global mass extinction and boundary marking end of the Mesozoic Era

Contents

Cretaceous–Paleogene

Introduction

The Cretaceous–Paleogene boundary marks a global biotic turnover associated with a mass extinction that affected dinosaurs, ammonites, and many marine and terrestrial taxa; this event is central to studies by researchers affiliated with the Smithsonian Institution, Natural History Museum, London, American Museum of Natural History, Geological Society of America, and teams from universities such as Harvard University, University of California, Berkeley, University of Chicago, University of Kansas, and University of Montreal. Major figures including Luis Alvarez, Walter Alvarez, Alvarez family research collaborators, Jan Smit, Gerta Keller, Helen Tappan, A. G. Fischer, and institutions like the U.S. Geological Survey, Conseil National de la Recherche Scientifique, and Royal Society have debated causes and consequences using data from sites such as Chicxulub, El Kef, Stevns Klint, Gubbio, and Hell Creek Formation.

The boundary is defined stratigraphically and chronometrically at about 66 million years ago, based on radiometric work by specialists at Massachusetts Institute of Technology, California Institute of Technology, Los Alamos National Laboratory, and laboratories using techniques developed by teams including Willard Libby and K. R. Ludwig, correlating sections in the Western Interior Seaway, Tethys Ocean, Gulf of Mexico, North Atlantic Ocean, and outcrops in Denmark, Italy, Spain, Mexico, and India. Geologists referencing concepts from the International Commission on Stratigraphy, Geological Time Scale 2012, and efforts by committees at the International Union of Geological Sciences integrate magnetostratigraphy, chemostratigraphy, and biostratigraphy with cores retrieved by projects such as IODP, ODP, and national surveys from Mexico, Cuba, Haiti, Brazil, and Argentina.

Hypotheses for the proximate cause include impact by a bolide linked to the Chicxulub structure, an idea propelled by work associated with Luis Alvarez and supported by drilling expeditions coordinated with the International Ocean Discovery Program and the Plymouth University-affiliated teams, and alternative or contributing explanations invoking the Deccan Traps volcanism analyzed by researchers at Indian Institute of Science, Geological Survey of India, and collaborations with Princeton University, Yale University, and University College London. The impact hypothesis connects evidence such as an iridium anomaly reported in studies by Luis Alvarez, shocked quartz documented by investigators from Lamont–Doherty Earth Observatory, spherules described by field parties at El Penón, and tsunami deposits examined by teams from University of Texas and National Autonomous University of Mexico. Volcanism models incorporate paleoclimate simulations developed by groups at National Center for Atmospheric Research, Met Office Hadley Centre, Max Planck Institute for Meteorology, and NASA Goddard Institute for Space Studies, which explore interactions with sea-level change documented by researchers at Scripps Institution of Oceanography and sedimentologists from University of Leeds.

The extinction led to the disappearance of non-avian dinosaur lineages recognized in faunas from Mongolia and North America, the loss of marine reptiles recorded in collections at the Field Museum, decline of ammonites and planktonic foraminifera studied by paleontologists at University of Cambridge and University of Copenhagen, and reshaping of plant communities observed by palynologists at Smithsonian Tropical Research Institute and Royal Botanic Gardens, Kew. Surviving lineages—avian dinosaurs, mammals, crocodilians, turtles, and many invertebrates—radiated during the Paleocene as documented in fossil assemblages from the Paleocene–Eocene Thermal Maximum research linked to teams at Columbia University, University of Edinburgh, and University of Bonn. Recovery dynamics have been explored using models from Stanford University, ETH Zurich, and Imperial College London integrating ecological theory advanced by scholars at Princeton University and University of Chicago.

Multidisciplinary approaches combine geochemistry (iridium anomalies, isotope excursions) by laboratories at Oak Ridge National Laboratory and Stockholm University, stratigraphy (boundary sections at Stevns Klint and Gubbio) curated by national museums in Denmark and Italy, geophysics (gravity and seismic imaging of Chicxulub) using instruments developed at Schlumberger and flight surveys coordinated with European Space Agency programs, and paleontology (taxonomic revisions) performed by curators at Natural History Museum, London, American Museum of Natural History, Royal Belgian Institute of Natural Sciences, and universities including University of Toronto and University of New Mexico. High-resolution dating employs argon-argon methods refined by researchers at University of California, Los Angeles and Arizona State University, while climate and impact modeling use supercomputers at Lawrence Livermore National Laboratory and methods published in journals by publishers such as Nature, Science, Proceedings of the National Academy of Sciences, and Geology.

The event reshaped paleontological priorities at institutions like Smithsonian Institution and Natural History Museum, London, inspired long-term programs at International Ocean Discovery Program and stimulated debates adjudicated in forums such as meetings of the American Geophysical Union, European Geosciences Union, and symposia at Royal Society and National Academy of Sciences. Its study influenced conservation narratives advanced by organizations including World Wildlife Fund and informed geological hazard assessment policies discussed at United Nations Environment Programme sessions, while continuing to drive new fieldwork in Mexico, Caribbean, Denmark, India, and Madagascar and laboratory advances at Caltech, MIT, and Max Planck Society.

Category:Mass extinctions