The Elements of Evolution (4) Extinction Events

Extinction Events

There have been many mass extinction events on Earth. (By convention, extinction events terminate a labeled geological period, age, or epoch.) 10 have been especially catastrophic: where most of the existing diversity succumbed. (Conventional accounting tallies only 5 major extinction events. In 2015, American biologists Peter Ward and Joe Kirschvink cited 10 such massive extinctions (omitting only the Botomian event).) Another such horrific extinction event is presently gaining momentum.

1. Great Oxidation Event (2.45 BYA) (W–K): marine cyanobacteria infuse the atmosphere and sea surface with oxygen, slaughtering anaerobes who couldn’t tolerate O2.

2. Snowball Earth (~800–630 MYA) (W–K): thick ice covers most of the planet in 3 episodes, dropping both diversity and biomass.

3. Ediacaran (period) (542 MYA) (W–K): early worms ravage marine microbial populations.

4. Botomian (age) (517 MYA): a severe extinction pulse in the Early Cambrian epoch.

5. Cambrian (period) (488 MYA) (W–K): many weird wonders lose their lease on life, including the first flush of trilobites, in an extinction event called the Dead Interval.

6. Ordovician (period) (455 MYA): glaciations again take their toll with wholesale extinction in the tropics.

7. Devonian (period) (374–364 MYA): a series of extinc-tion pulses involving invasive species and volcanoes.

8. Permian (period) (252 MYA): Earth’s most severe mass extinction event – the Great Dying.

9. Triassic (period) (201 MYA): life on land and in the oceans takes a major hit from volcanic climate change.

10. Cretaceous (period) (66 MYA): the finale for large dinosaurs.

The chronicle of mass extinction events is incomplete. New discoveries keep being made of extinction pulses which profoundly affected life.