There are several short-lived time periods in Earth’s history during which a significant percentage of species in the faunal and floral realms went extinct. The most recent one in ancient geologic history took place about 66 million years ago with the demise of the dinosauria. John Geissman highlights several of these extinction events and discusses the processes that significantly disturbed the ecological realm at these times.

John Geissman is a professor emeritus of geoscience at the University of Texas at Dallas and the University of New Mexico. He received a BS, MS, and PhD in Geology (now Earth and Environmental Sciences) from the University of Michigan. He is a Past President of the Geological Society of America as well as the editor for the GSA Bulletin. He has over 300 peer-reviewed science journal contributions.