Earth Sciences 2240F/G Chapter Notes - Chapter 17: Background Extinction Rate, Ordovician, Cambrian
13 Feb 2018
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Chapter 17: phanerozoic eon a trip through time. Phanerozoic eon extends from 542mya: phanerozoic = abundant life" so, time represented by abundant fossil evidence in the rock records. Cambrian (542-488mya) the seas advanced over the edges of the fragments of rodinia, forming numerous shallow and warm bodies of water where life exploded". New organisms didn"t simply appear out of nowhere: evolved from precambrian beginnings. Background extinction rate was high: over this were 2 periods of strong mass extinction, each accounts for demise of ~40% of marine genera. Sir"s preference: glacial cooling + lowering of sea levels. As gondwana drifted south and glaciers built on it, volcanism subsided, climate cooled, and ocean waters were ~ same as today by early-middle ordovician. By middle-late ordovician, 2 of the biggest blocks began to move toward each other w/ resultant volcanoes on the subduction boundary: resulted in a strong volcanic period and strong greenhouses (turned the planet into a hothouse)
