WHAT CAUSED THE GREATEST OF ALL MASS EXTINCTIONS, AT THE END OF THE PERMIAN?

The most spectacular biotic turnover in the Phanerozoic took place at the Permian-Triassic boundary, affecting both marine and terrestrial organisms. Thus it is estimated that about half of all marine invertebrate and terrestrial vertebrate families went extinct at the end of the Palaeozoic. This turnover marks the time of a pronounced shift in the dynamics of animal diversification, with the magnitude of changes in diversity being influenced in the Palaeozoic more by change in extinction rate but after the Palaeozoic by changes in origination rate. To take just one example at a more specific level, brachiopods are replaced by bivalves as the dominant marine benthic macro-invertebrates.

Six different mechanisms have been proposed to account for the extinction event: marine regression, global cooling, hypercania, or poisoning by excess CO2 in the sea, bolide impact, transgression and associated spread of anoxic waters, and global warming. As a result of intensive investigations within the last two decades in biostratigraphy, facies analysis and geochemistry in regions extending across the world, we are now in a strong position to evaluate these various proposals in the light of a wide range of evidence.