A scale of greatness and causal classification of mass extinctions: implications for mechanisms.
A quantitative scale for measuring greatness, G, of mass extinctions is proposed on the basis of rate of biodiversity diminution expressed as the product of the loss of biodiversity, called magnitude (M), and the inverse of time in which that loss occurs, designated as intensity (I). On this scale, the catastrophic Cretaceous-Tertiary (K-T) extinction appears as the greatest since the Ordovician and the only one with a probable extraterrestrial cause. The end-Permian extinction was less great but with a large magnitude (M) and smaller intensity (I); only some of its individual episodes involved some semblance of catastrophe. Other extinctions during the Phanerozoic, with the possible exception of the end-Silurian diversity plunge, were parts of a forced oscillatory phenomenon and seem caused by marine- and land-habitat destruction during continental assemblies that led to elimination of shelves and (after the Devonian) rain forests and enlargement of deserts. Glaciations and orogenies that shortened and thickened the continental crust only exacerbated these effects. During the Mesozoic and Cainozoic, the evolution of life was linearly progressive, interrupted catastrophically only at the K-T boundary. The end-Triassic extinction was more like the Paleozoic extinctions in nature and probably also in its cause. By contrast, the current extinction resembles none of the earlier ones and may end up being the greatest of all.
Sengör
A M Celâl
AM
Maden Fakültesi, Jeoloji Bölümü, Istanbul Teknik Universitesi, Ayazağa 34469, Istanbul, Turkey. sengor@itu.edu.tr
Atayman
Saniye
S
Ozeren
Sinan
S
D000818:Animals; D044822:Biodiversity; D053476:Extinction, Biological; D008954:Models, Biological; D013997:Time Factors
Science. 1982 Mar 19;215(4539):1501-3
17788674
Proc Natl Acad Sci U S A. 2001 May 22;98(11):6261-6
11353852
Science. 1965 Jun 25;148(3678):1696-9
17819414
Science. 1987 Nov 27;238(4831):1237-42
17744360
Science. 1980 Jun 6;208(4448):1095-108
17783054