Catastrophes & Mass Extinctions
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The earth has evolved in geologic terms, but it has also evolved in terms of the life that teems upon it. All the change that can be seen and inferred has to be explained. The argument in the eighteenth and nineteenth centuries was divided into two camps, the catastrophists and the uniformitarianists. The catastrophists explained the changes by resorting to cosmic violence, to a succession of catastrophes that bring about change suddenly. The uniformitarianists saw the earth evolving in a uniform manner over time. Both groups agreed that catastrophes do play a role in the evolution of the earth and that catastrophes still occur to reshape portions of the earth's surface or to bring about biological changes in a relatively short time. However, this is different from holding that a cosmic catastrophe has to be posited to explain change. One of the more dramatic biological changes in the history of the earth was the extinction of the dinosaurs. This was not the only such extinction to take place, but the size of the beasts involved, the length of time they ruled the earth, and the hold they have on the public imagination makes the extinction of the dinosaurs of particular note. Several theories have been offered for the extinction of the dinosaurs, among them genetic theories, theories of climatic change, and the currently accepted view that a comet or meteorite hit the earth, created conditions we might liken to nuclear winter, and killed much of the life on earth at
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ling is continental glaciation, and so the coming of an ice age has been suggested (McGhee 132-133). The first great extinction took place 1.4 billion years ago with the extinction of the acritarchs, the durable dormant stages of single-celled algae. This extinction has been linked with a major period of continental glaciation. The connection is not firmly established but is suggestive (Stanley 53-54).
Ginsburg suggested in 1964 that mass extinctions coincided with regressions of the sea, which can also be caused by glaciation as More water is frozen into ice. Ginsburg noted that each major division in the geological time scale begins with a marine transgression (the spread of the sea over land areas) accompanied by the appearance of a new fauna, and each ends with a marine regression (the retreat of the sea) which is contemporary with a mass extinction. Ginsburg finds it "hard to believe that the simultaneous occurrence of marine regressions and mass extinctions over a period of 600 million years could have been fortuitous. There must have been a direct cause and effect relationship between the fluctuations of sea level and the renewal of animal life in the course of geological time" (Ginsburg 44).
Ginsburg further notes
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Approximate Word count = 2183
Approximate Pages = 9 (250 words per page)
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