This lesson introduces extinction events and explains why scientists identify a group of especially severe events as the "Big Five." It also compares the major biological consequences of each event.
An extinction event, also called a mass extinction or biotic crisis, is a widespread and rapid decrease in Earth's biodiversity. Scientists identify one by a sharp fall in the diversity and abundance of multicellular organisms. Extinction is occurring all the time, but an event becomes exceptional when the extinction rate rises relative to both the usual background extinction rate and the rate at which new species arise through speciation.
All flashcards
Mass extinction
A widespread, rapid decline in biodiversity when extinction rises relative to background rates and speciation.
Press/pulse model
A framework in which sustained environmental stress can weaken ecosystems before a sudden shock pushes them past a threshold.
Flood basalt
An exceptionally large volcanic episode that produces extensive igneous rock and can disrupt climate and ecosystems.
Signor–Lipps effect
An abrupt extinction can appear gradual because species’ last preserved fossils occur at different times.
Adaptive radiation
Diversification of surviving lineages into ecological opportunities, such as niches left open by extinction.
Quiz questions
In the press/pulse model of mass extinction, how can a press and a pulse combine?Answer: Sustained stress weakens ecosystems, and a sudden shock may push them past a threshold.
What does rarefaction help researchers do when comparing fossil collections?Answer: Compare collections while accounting for differences in sample size.
What did the 2019 IPBES global biodiversity assessment estimate about threatened species?Answer: About one million plant and animal species were threatened out of roughly eight million.
Why can an extinction create an opportunity for adaptive radiation?Answer: The loss of established groups can leave ecological niches available to surviving lineages.
Why is the scale of the Great Oxidation Event difficult to compare with the Big Five?Answer: Limited knowledge of earlier microbial ecosystems makes the scale of their losses difficult to assess.
Based on the Wikipedia article Extinction event, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.