Mass extinctions in the Phanerozoic: a single cause and if yes which?
December 4, 2002. Louis Clark Vanuxem Lectures
Asteroid impact, massive volcanism, sea-level changes, anoxic events, or mechanisms related only to biological population dynamics have all been considered as possible causes of mass extinctions. I will review recent progress in dating continental flood basalts and show that in an increasing number of cases the correlation with a mass extinction is compatible with the most accurate data. I will spend some time on the Deccan (KT extinction), Parana (end of Jurassic), Central Atlantic Magmatic Province (end of Triassic) and Siberian traps (the great Permo-Triassic extinction), and discuss recent results for the Ethiopian traps at 30 million years, Emeishan traps at 258 million years (the end-Guadalupian extinction), and suggest that the traps responsible for the 360 million year Frasnian-Famennian extinction may have been found. In contrast, the KT impact remains the only well documented case and many impacts do not correlate with a mass extinction. One can now ask what is the share of impact versus Deccan in the KT extinction, and how much the impact would have achieved alone without the flood basalt. Sea level variations will also be considered and can rather readily be associated with flood basalts, suggesting that the internal pulsations of Earth geodynamics and plate tectonics exert the principal control on the few, brief episodes when “survival of the fittest” was replaced by “survival of the luckiest”.