Summary: O Wonder! How many goodly creatures are there here! —Shakespeare The Cambrian Explosion was not a violent volcanic eruption, but rather the sudden appearance in the fossil record of abundant and diverse shelly fossils, the remains of relatively large animal life. Even Charles Darwin recognized it, and saw it as an important objection to his theory of evolution by natural selection. Like most geologic events the Cambrian explosion wasn’t instantaneous, but it did occur over a geologically short time, around 542 to 530 million years ago, right at the start of the Cambrian period of the Paleozoic Era. Today’s podcast is a discussion between me and geologist Dr. Colleen Elliot. Neither of us is an expert on paleontology, so this will be something of an exploration for all of us. Here are some definitions of terms non-geologists may be unfamiliar with in the discussion. Phanerozoic is the name of the eon, the largest subdivision of geologic time, that starts with the Cambrian period of the Paleozoic era. We talked about that a bit the other day. And the Great Unconformity is a break in the rock record that is nearly global in extent, a time before the first rocks of the Cambrian were deposited. It represents a time of near-global erosion of the older Precambrian rocks, and it means that the continents were standing above sea level so that they could be eroded. —Richard I. Gibson Links for further reading: McKenzie et al. on climate and evolution (January 2014) http://www.sciencemag.org/content/341/6152/1355 Smith and Harper on summarizing Cambrian explosion causes (Sept. 2013) http://www.astrobio.net/pressrelease/5758/oxygen-not-the-cause-of-the-cambrian-explosion https://www.pbs.org/wgbh/evolution/library/03/4/l_034_02.html http://ucrtoday.ucr.edu/9063
