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Home Uncategorized The Great Dying

The Great Dying

John Bannigan
The Worst of Times. How Life on Earth Survived Eighty Million Years of Extinctions, by Paul B Wignall, Princeton University Press, 199 pp. ISBN 978-0691142098 Until the 1980s, earth scientists and evolutionary theorists rejected the possibility of mass extinctions caused by cataclysmic geophysical upheavals or meteor strikes. But now it is accepted that at least twenty such events occurred during the past 542 million years. The Worst of Times, written by the professor of palaeoenvironment at the University of Leeds, is an account of the severest of these, the Permian-Triassic extinction, which began 252 million years ago and resulted in the elimination of ninety-five per cent of plant and animal species. Before discussing the book it is worthwhile to look at the reasons why geologists and biologists rejected the mere possibility of mass extinction until advances in geochemistry and palaeontology made their reality inescapable. In the eighteenth and early nineteenth centuries the study of geological strata and their contained fossils made it obvious that there was a progression in the presence of simpler to more advanced forms from the older to the younger strata. So striking is this progression that geologists distinguished the main phases of the formation of the lithosphere on the basis of the contained fossil fauna. First they saw layers that were seemingly devoid of fossils. Above these were strata which, as well as containing the remains of shellfish, sponges, arthropods etc, also contained examples of non-mammalian vertebrates, mainly fish, but also early amphibia and reptiles. These layers were ascribed to the Palaeozoic or ancient era. This was followed by the Mesozoic or middle era, when the first mammalian forms appeared. Thirdly, there is the recent or Cenozoic era, during which the main taxonomic groupings of animals and plants evolved into their present-day forms. These eras are further divided into nested sub-intervals (periods, epochs, ages and so on) based on finer details of faunal classification or on geological features. Needless to say, the early palaeontologists reasoned that their failure to find any or only few fossils in pre-Palaeozoic formations was because the fauna existing then did not have body parts which favoured fossilisation, such as bones, teeth or shells. Another thing that was realised early on was that species disappeared from the fossil record as new forms appeared. At present 1.2 million species are catalogued in the biological databases but many taxonomists think that the real number could…



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