Utilizing the easy dates marking the finish of assorted intervals (e.g., 145 MYA = finish of Jurassic interval),
what fraction of earth’s historical past occurred after
1. the “Cambrian explosion” (aka the begin of the Phanerozoic eon and Cambrian interval)
2. the end-Cretacious mass extinction (aka the begin of the Cenozoic period and Paleogene interval)
three. the emergence of our species Homo sapiens (at about 200,000 years in the past)
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