the "Cambrian explosion"

the “Cambrian explosion”

Using the simple dates marking the end of various periods (e.g., 145 MYA = end of Jurassic period), what fraction of earth’s history occurred after 1. the “Cambrian explosion” (aka the start of the Phanerozoic eon and Cambrian period) 2. the end-Cretacious mass extinction (aka the start of the Cenozoic era and Paleogene period) 3. […]