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Lecture 6: Extinctions a global environmental process 1. Major extinctions 2. Theories of episodicity 3. Focus on the K-T 4. Implications for global diversity Sepkoski’s Curves An analysis of shallow marine diversity through time Family diversity Ord Dev P Tr Cambrian fauna Ordovician radiation End Permian extinction Diversity = evolution - extinction Cret Mass extinction End Ordovician Biological expression About 70% of marine species became extinct. Tropical faunas in general were badly damaged, especially reefs. Main affected groups were trilobites, graptolites, echinoderms and brachiopods. Probable causes A sudden, major glaciation, spreading from the South Pole. Most of the tropical belt disappeared. Sea levels fell, reducing the shallow shelf area, and cold water faunas moved to low latitudes, excluding warmer water ecosystems. End Devonian A series of events lasting about 10 My. This extinction was characterised by low rates of origination and extinction rates as such remained unexceptional. Cephalopods, fish, corals most affected. The least understood mass extinction. Seabed anoxia or extraterrestrial impact have been cited. Another suggestion is that the marine ecosystem was badly affected by the rise of land plants and a short-lived drawdown of CO 2. End Permian The largest mass extinction, removing 95% of marine species and over 50% of marine families. Trilobites, cephalopods, corals, bryozoans and crinoids badly affected. Major faunal and floral overturn on land. Marks the boundary between dominance by the Palaeozoic and Modern fauna. Event may relate in some way to the supercontinent of Pangea, which would have affected world climates and oceanic conditions. The largest terrestrial igneous province was emplaced in Siberia at this time, and would have changed climate over a range of timescales. There is controversial evidence for meteorite impacts at this boundary. End Triassic A multiple event again. Most important on land, where floral overturn exceeded 95%. Around 30% of marine species became extinct, mainly reef dwellers including ceratite ammonites, brachiopods and bivalves. Recent work suggests that widespread submarine volcanic activity may have been responsible for massively elevated CO2 levels at this time. This volcanic activity was a function of the break-up of Pangea. End Cretaceous Dinosaurs, marine and aerial reptiles, ammonites, belemnites became extinct. Brachiopods, bivalves and foraminifera severely affected. Most commonly attributed to a major meteorite impact into the Yucatan area of Mexico. Underlying sulphates and limestones would have vapourised to produce acid rain. Short term cooling (from dust and sulphur dioxide) and long term warming from carbon dioxide) resulted. Also linked to the Deccan Igneous province in India. The K-T Boundary 65 Ma ago 65% extinction Oceans Survival Guide Near surface High latitude Simple skeleton, not limy Small size, cysts Land Survival Guide Small size Ferns Detritus feeder Iridium spike Microtektites Shocked quartz Plate tectonics Deccan Traps A Large Igneous Province (LIP) Mantle structure Mantle heterogeneity Mantle Plumes Possible cooling effects Deccan effects Eruptions reached troposphere Gases - carbon dioxide, sulphur dioxide, hydrogen chloride Ash Atmosphere cools then heats, perhaps by 100 C Ozone destroyed Eruptions from fissures 400 km long Terrestrial eruptions maximum effect on atmosphere Oceans become acidic Extinction correlation 6. End Cretaceous event 30% families extinct 65% species extinct Dinosaurs, marine and flying reptiles, ammonites extinct. Two likely causes a. Meteorite impact b. Deccan Trap volcanism Iridium spike Shocked quartz Microtektites Cretaceous Palaeogene Yucatan impact crater Crust Mantle plumes D’’ layer Core Deccan traps Sepkoski’s Curves An analysis of shallow marine diversity through time Family diversity Ord Dev P Tr Cambrian fauna Ordovician radiation End Permian extinction Diversity = evolution - extinction Cret