BIOL 2200 Lecture 9: 02/06/2017: 531-543 ~ Extinctions, Radiations, and Evolutionary Trends
6 Feb 2017
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Cambrian explosion = when most extant phyla appeared. Sudden appearance of complex organisms with mineralized skeletons. Otherwise we would be in a static world. Most of the species that have ever lived are now extinct. There have been five mass extinctions where there was a big loss of species. Marine animals are a good reference because we have an extensive fossil record of them. Mostly marine species are affected because they were the most diverse. Likely global cooling, anoxic oceans, and slow. Led to the rise of the dinosaur. Decrease in speciation rather than increase in extinction. Debris from an asteroid in the atmosphere led to rapid cooling. The debris blocked the sun, not allowing the heat to reach the earth. Current rates of extinction are 100x higher than the background extinction rate. We are not there yet, but we are on track for another mass extinction. We may be too far along to reverse the extinction.
