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lecture_15 - Catastrophes and Evolution Extinction was not...

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Catastrophes and Evolution Extinction was not widely accepted before 1800. Extinction was established as a fact by Georges Cuvier in 1796, and was critical for the spread of uniformitarinism in spite of the fact that Cuvier viewed extinctions as evidence in favor of catastrophism and opposed Lamarckian evolution theories. Over 99% of all species that have ever existed are now extinct. Extinctions occur at an uneven rate. There have been 6 major and many minor (up to 20) extinctions observed in the fossil record. Nearly all divisions among geological eras, eons and periods are marked by extinctions and originations. Cambrian-Ordovician transition 488 Myr A series of extinctions that eliminated many brachiopods and tribolites. Ordovician-Silurian transition 444 Myr Second largest extinction. Late Devonian 360 Myr A series of extinctions near the Devonian-Carboniferous transition, lasted 20 Myr with several pulses. Permian-Triassic extintinction 251 Myr Earth’s largest extinction killed 96% of all marine species and 70% of land species (plants, insects, vertebrates). Ended dominance of mammal-like reptiles and led to dinosaur dominance. Triassic-Jurassic extinction 200 Myr Last of large amphibians extinguished. Cretacious-Tertiary extinction 65 Myr About 50% of all species, including dinosaurs, were extinguished. Holocene extinction, now About 70% of biologists view the present as a mass extinction, due to human intervention. Not universally accepted as many argue there are significant differences from extinctions. Lattimer, AST 248, Lecture 15 – p.1/23
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Major Extinctions Rohde & Muller, Nature, 2005 Lattimer, AST 248, Lecture 15 – p.2/23
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Theories of Extinctions A theory should explain all the losses, not just a few groups like dinosaurs explain why some organisms survived and others didn’t be based on events that actually happened. Flood basalt events, triggered by extensive volcanic activity, have been recorded 11 times and each is connected to an extinction event. Sea level falls have been recorded 12 times and 7 are associated with extinctions. Asteroid impacts producting craters over 100 km wide have been recorded once and associated with a mass extinction. These could produce intense volcanic activity as well as prolong heating or cooling due to deposition of soot and aerosols into atmosphere. Asteroid impacts producing craters less than 100 km wide have been recorded over 50 times, but most not connected to any extinctions.
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