ENVS 2420 Lecture Notes - Lecture 5: Background Extinction Rate, Extinction, Global Cooling

• School: York University
• Department: Environmental Studies
• Course: ENVS 2420
• Professor: Laforet

Document Summary

Fossil record suggest that all species have a finite life span. Background extinction --> the cessation of existence of a species through environmental or biological factors, reducing factors (rate-=0. 1-1 species per million species year) ^ typically don"t include climate change into background extinction: use fossil record to study pre-historic extinctions, primarily based off marine invertebrates (best preserved) -> 27% of all families, 57% of all genera lost. -> hypothesized global cooling event: devonian (375 mya) -> 19% of all families, 50% of all genera lost. -> hypothesized global cooling: permian (251 mya) -> 57% of all families, 83% of all genera. -> multiple causes hypothesized: triassic (205 mya) -> 23% of all families, 48% of all genera lost. -> many reptiles and last of large amphibians lost. -> causes largely unknown: late cretaceous event (65 mya) -> 17% of all families, 50% of all genera lost. -> 36/89 tetrapod families disappear including dinosaurs, plesiosaurs, pterosaurs: holocene (6th mass extinction)