▫ The episodic adventures of organisms have been periodically punctuated by extinction events that punked life’s prospects.
▫ Mass extinction events have invoked dramatic changes in dominant life forms. Mass extinction events ranging over a spectrum of intensity have been episodic in Earth’s history.
Mass extinctions are largely indiscriminate. The only selection factor in extinction events is tolerance to adversity. The hardiest organisms are the most archaic: microbes, but they too go extinct.
▫ High extinction rates are typically followed by a recovery with high species origination rates within a few million years. The availability of nutrients is a key factor in regeneration of life; hence, for animals, the criticality of algae and plants. Adaptive ability during an ongoing extinction event determines the event’s severity and longevity in relation to biota.
▫ The causes of extinction events are various, ranging from sudden impacts from space, radiation, geomagnetic reversals, volcanism, continental drift, and global climate change. These factors are often intertwined in increasing the severity of mass extinction.
▫ The worst extinction event to date was the Great Dying, at the Permian–Triassic (P–T) period boundary, beginning 252 MYA. The mass extinction event underway now may be its equal.