Periodic mass extinctions at random.Periodic mass extinctions at random Gazing into the rock and fossil record, some geologists and paleontologists have found various periodicities to the mass extinctions that punctuate punc·tu·ate v. punc·tu·at·ed, punc·tu·at·ing, punc·tu·ates v.tr. 1. To provide (a text) with punctuation marks. 2. the earth's history. These extinctions wiped out 50 percent to 95 percent of the species living at the time, and they seem to repeat with an interval of 26 million to 30 million years. To explain the apparent pattern, scientists have invoked cyclic meteor showers Table of meteor showers Name Dates Peak dates ZHR Rating Quadrantids Jan 1-Jan 5 Jan 3 15:20 +49 41 120 Strong Gamma Velids Jan 1-Jan 15 Jan 5 08:20 -47 35 2 Weak Alpha Crucids Jan 6-Jan 28 Jan 15 12:48 -63 50 3 Weak , galactic rotation and other periodic events. But more recently, paleontologist Steven Stanley Steven J. C. Stanley is a Jamaican audio engineer, record producer and keyboardist who has worked in the reggae, dub and rock music genres since 1975, most notably with Talking Heads, Tom Tom Club and Black Uhuru. of Johns Hopkins University Johns Hopkins University, mainly at Baltimore, Md. Johns Hopkins in 1867 had a group of his associates incorporated as the trustees of a university and a hospital, endowing each with $3.5 million. Daniel C. in Baltimore theorized that random catastrophic events could generate periodic mass extinctions. Michael L. McKinney of the University of Tennessee The University of Tennessee (UT), sometimes called the University of Tennessee at Knoxville (UT Knoxville or UTK), is the flagship institution of the statewide land-grant University of Tennessee public university system in the American state of Tennessee. in Knoxville now reports that computer models support Stanley's theory. McKinney's model simulates the diversity of species through time, and into the model he incorporates a random series of environmental upheavals. Scientists have compiled a long list of events--such as comet impacts, rises in sea level and massive volcanic eruptions-- that could individually stimulate extinctions. Since these events are often unrelated to each other, says McKinney, it is safe to assume that the total list of catastrophic events would form a random pattern. As expected, McKinney found that a single event drastically reduces the number of different species. But following this first event, the system is temporarily "immune' to random cataclysms The cataclysm is the Greek expression for the Biblical Great Flood of Noah, from the Greek kataklysmos, to "wash down." Erudite Bible studies drew it into the English language in 1633. . According to according to prep. 1. As stated or indicated by; on the authority of: according to historians. 2. In keeping with: according to instructions. 3. McKinney, the species that survive a mass extinction are particularly hardy and are "resistant' to subsequent random changes. Moreover, after an extinction, there are simply fewer species left to die out. "Therefore,' he says, "until many species have evolved, including extinction-"prone' types, any intervening catastrophes would have little effect.' After each extinction, the biological community requires a distinct recovery period before it is again ready to go out with a bang. |
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