End-Ordovician extinction

End-Ordovician extinction
Name	End-Ordovician extinction
Period	Ordovician
Time	~443 million years ago
Severity	Severe (second-largest marine extinction)
Possible causes	Glaciation; sea-level change; volcanic activity; anoxia

End-Ordovician extinction The End-Ordovician extinction was a major Phanerozoic biotic crisis near the close of the Ordovician Period that drastically reduced marine biodiversity. Influential paleontologists, stratigraphers, and geochemists have linked the event to climatic cooling, eustatic sea-level change, and perturbations recorded in Ordovician strata studied by field teams from institutions such as the United States Geological Survey, Natural History Museum, London, and the Smithsonian Institution. International research programs coordinated by organizations like the International Commission on Stratigraphy and the International Union for Geological Sciences continue to refine correlations among classic sections in regions including Antarctica, North America, Baltica, Siberia, Gondwana, Wales, Scotland, Ireland, Morocco, and China.

Overview

The extinction eliminated a large fraction of marine genera and reshaped Paleozoic ecosystems studied by researchers at universities such as Harvard University, Yale University, University of Cambridge, University of Oxford, University of Chicago, and University of California, Berkeley. Key fossil groups documented in museum collections at the Natural History Museum of Los Angeles County and the Royal Ontario Museum—including brachiopods, trilobites, bryozoans, and graptolites—show contraction in geographic ranges mapped by geologists from the Canadian Geological Survey and the Geological Survey of India. The event is commonly placed stratigraphically near the boundary preserved in type sections formalized by panels of the International Geological Congress.

Timing and Phases

Stratigraphic studies by groups at the Bureau de Recherches Géologiques et Minières and the Geological Survey of Japan identify two main pulses separated in time, a pattern first noted in classic work by field teams led by scientists affiliated with Trinity College Dublin and University College Dublin. Biostratigraphers using conodont and graptolite zonations developed at institutions like the Palaeontological Association and the Royal Society correlate phases across basins from South America to Antarctica. Radiometric calibration efforts involving laboratories at the Max Planck Institute for Chemistry and the US Naval Research Laboratory refine ages using isotopes tied to stratotypes designated by the International Stratigraphic Guide.

Causes and Mechanisms

Hypotheses advanced by researchers at the Lamont–Doherty Earth Observatory, the Scripps Institution of Oceanography, and the Woods Hole Oceanographic Institution emphasize glaciation on the Late Ordovician supercontinent of Gondwana and associated eustatic sea-level fall. Studies published by teams from the Massachusetts Institute of Technology, California Institute of Technology, and the University of Leeds invoke climate forcing, ocean circulation changes, and nutrient fluxes documented in proxy records analyzed at the Plymouth Marine Laboratory and the Alfred Wegener Institute. Alternate models proposed by scientists at the US Geological Survey and the Chinese Academy of Sciences explore volcanic degassing, large igneous province analogies, and weathering effects measured by isotope laboratories such as those at the ETH Zurich and the University of California, Los Angeles. Geochemical work coordinated with the European Geosciences Union examines carbon isotope excursions, oxygen isotope trends, and strontium isotope shifts interpreted by teams at the Royal Society of Chemistry and the American Geophysical Union.

Biotic Impact and Extinctions

The extinction pattern, documented in monographs from the Palaeontological Society and the British Geological Survey, disproportionately affected shallow-shelf faunas including articulate and inarticulate brachiopods curated at the Smithsonian Institution National Museum of Natural History and trilobites housed at the Field Museum of Natural History. Graptolite turnover recorded by specialists associated with the Natural History Museum, London and the Finnish Museum of Natural History marks major planktonic losses, while conodont assemblages studied by researchers at the University of Copenhagen show range reductions. Paleobiologists at the University of Chicago and the University of Michigan used quantitative methods developed with support from the National Science Foundation and the Royal Society to assess extinction selectivity, ecological restructuring, and the collapse of reef-like carbonate communities recognized from sections in Morocco and Spain.

Recovery and Aftermath

Post-extinction radiations studied by paleontologists at the Smithsonian Institution and the American Museum of Natural History record the rise of new brachiopod and mollusk faunas, with diversification patterns interpreted by macroevolutionary researchers affiliated with the University of Bristol and the University of Kansas. Global oceanographic shifts reconstructed by teams from the National Oceanic and Atmospheric Administration and the Jet Propulsion Laboratory influenced habitats across continental shelves emphasized in syntheses presented at meetings of the Geological Society of America and the European Union of Geosciences. Subsequent Ordovician–Silurian boundary work by stratigraphers at the Royal Society and the International Commission on Stratigraphy frames longer-term biodiversification trends culminating in Silurian ecosystems studied at the Natural History Museum of Denmark.

Geological and Geochemical Evidence

Evidence derives from sedimentary sequences analyzed by geoscientists at the Geological Survey of Canada and the British Antarctic Survey, including glacial tillites in Morocco and erosional unconformities in Laurentia. Carbon isotope excursions measured by laboratories at the University of Göttingen and the University of California, Santa Cruz coincide with sea-level indicators mapped by researchers at the Geological Survey of Norway and the Bureau of Meteorology, Australia. Redox-sensitive trace element studies processed at the Max Planck Institute for Marine Microbiology and the University of Barcelona reveal episodes of anoxia and euxinia identified in cores curated by the International Ocean Discovery Program. Palynological and microfossil records examined at the Natural History Museum, London and the Australian National University further constrain environmental shifts, while integrative syntheses appear in journals supported by the Royal Society and distributed via the American Association for the Advancement of Science.

Category:Extinctions