Lecture_18_Mass_extinctions

Lecture_18_Mass_extinctions - Mass Extinctions E x ti n c...

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1 Mass Extinctions • Extinction rates through time • End Permian extinction • End Cretaceous extinction
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2 Diversity increases as specialists gradually replace generalists. Then have a steady number of species (rate of speciation = rate of extinction)
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3 • 99.9% of all species which have existed are now extinct • Extinctions occur continually in geologic record – Background extinction – Mass extinction • Extinctions correspond to divisions of geologic time (first defined by fossil assemblages)
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4 Mass Extinctions (Big 5) Age (my) % genera destroyed 435 Ordivician 57 350 Devonian 230 Permian 72 190 Triassic 65 Cretaceous 47
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5
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6 Extinction of species occurs 1. All the time 2. Only at boundaries between geologic time periods 3. Only after 500 million years ago
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7 Permian Extinction: 90% of ocean species 70% reptile and amphibian families 30% of insect orders -- only mass extinction documented for insects
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8 Potential causes for mass extinctions • internal ecological catastrophe • periods of intense volcanism • continental drift and sea level drop - habitat loss • global cooling and glaciation • ocean anoxia • extraterrestrial impact
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Permian Extinction: 1) Extensive volcanism: Siberian Traps are a massive lava flow (1.5 million km 3 ). Within the errors on the dating methods occurred at same time as extinctions. 2) Changes in ocean chemistry • carbon isotopes suggest imbalance in organic carbon burial and build-up of carbon in ocean and atmosphere. • Lack of benthic organisms suggest oxygen-free deep
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This note was uploaded on 02/08/2011 for the course EAS 1601 taught by Professor Lynch during the Spring '08 term at Georgia Tech.

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Lecture_18_Mass_extinctions - Mass Extinctions E x ti n c...

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