BIOL 117 Lecture Notes - Lecture 29: Shocked Quartz, Extinction Event, Global Cooling
Document Summary
Background extinction: normal rate of extinction, occurring all the time: emerging disease, predation pressure, etc. Mass extinction: when 60% or more of species go extinct, no correlation: not necessarily linked to tness under normal conditions. Random: result from sudden temporary changes in the environment. End-permian extinction: resulted in the disappearance in 90% of the species at the time, causes unknown, but thought to be because of warming, reduced sea level, and reduced oxygen levels i the water. End-cretaceous extinction: impact hypothesis: the extinction was related to an impact with an asteroid to the earth. Support for this hypothesis comes from high levels of iridium n sedimentary rocks formed at the cretaceous-paleogene boundary. Shocked quartz and micro-tektites found only at documented meteorite site. Huge crater off mexico"s yucatan peninsula: 60% to 80% of species went extinct. Nature of the impact: data indicate the asteroid was about 10km across, consequences of the impact likely included.
