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By Tony Hallam

Great up to date directory of major extinction occasions in earth historical past and disertion at the major nonetheless accredited theorites explaining manner those occurred. No mammoth novelties or radical thoeries yet a few issues have been new for me just like the frozen methan gases gathered in large cuantities within the backside of chilly seas and the prospective climatic alterations which may be cuased via them in the event that they are realesed to the atmospher by way of larger ocean water temperatures.

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Catastrophes and Lesser Calamities: The Causes of Mass Extinctions

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A particular taxon may be reported as becoming extinct at a stratigraphic horizon, whereas all it has done is evolve into its descendant. The overall consequence for the study of mass extinctions is that traditional taxonomic methods have probably overestimated the extent of extinction. This means that whereas the ‘big five’ mass extinctions still stand out significantly from background extinctions, some of the lesser events that have been claimed may be open to question. Those events that can, after rigorous analysis, be genuinely classed as catastrophic in a geological sense are unlikely ever to be pinned down in time more precisely than to a few tens of thousands of years, although exceptionally this limit may be reduced to a few thousand years.

1). In the summer of 1979, while Walter Alvarez was in Italy doing fieldwork, his father set himself the task of finding an explanation for the huge iridium enrichment. For a while he toyed with the possibility that it could be explained by a nearby supernova explosion, but it turned out that the platinum-244 isotope that ought to characterize a supernova deposit was not present. So another hypothesis was required. Further research had revealed that the iridium anomaly was essentially confined to the thin boundary clay, and that the iridium content quickly declined to normal background levels above and below in the stratal section.

There is even a fairly new ‘catastrophe theory’ in mathematics, put forward by the Frenchman René Thom, which had quite a vogue in the 1970s before being rather eclipsed by chaos theory. It postulates that a gradually 18 Historical background changing cause may be reflected, not in a gradually responding effect, but by a sudden shift from one stable state to another. This could well be relevant to crustal tectonics, in which the slow accumulation of stress could be relieved episodically by violent and destructive earthquakes.

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