Moritz11Notes - Biology 1BEvolution Lecture 11 Insights...

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Moritz Lecture 11 Notes - 1 Biology 1B—Evolution Lecture 11 (March 19, 2010), Insights from the Fossil Record and Evo-Devo Extinction Important points on extinction rates: Background rate of extinctions per million species per year: About 1 extinction per million species per year, so if there are roughly 10 million species on the planet, that would imply that about 10 species go extinct per year Environmental pressures, such as changing temperatures or volcanism, commonly cause extinction of species, but extinction also occurs in a “constant” environment Broadly, a typical species lasts 2-10 million years Figure 25.14 (page 521, 8 th edition) Huge extinction the result of a comet impact (more below) Cretaceous-Paleogene (Tertiary) Extinction—K/T Boundary Most importantly, this marked the demise of the dinosaurs (save for modern dinosaurs, which are birds) With the end of the dinosaurs came the adaptive radiation of the mammals Luis and Walter Alvarez (of UC Berkeley!) worked to find what caused the K/T boundary/extinction of the dinosaurs --Walter, a paleonotologist, noticed a layer of dark silt between fossils of organisms between the Cretaceous (large-bodied animals) and Paleogene (smaller-bodied animals) --He asked his father, a physicist, what might be studied in the isotopes in the dark silt layer
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Moritz11Notes - Biology 1BEvolution Lecture 11 Insights...

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