Word: raup
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...well. For example, the double- star systems that make up the majority of stars in the galaxy were long thought to be too unstable to support planets that could settle into regular orbits and give rise to life. But if the sun is part of a celestial duet, says Raup, then "the whole evolutionary process may thrive on this kind of disturbance...
Under the Raup and Sepkoski model of cyclical changes, the world is periodically wiped clean, leaving the evolutionary process with an empty slate...
...this point, Raup and Stepkowski reentered the picture. They used the observations of thousands of scientists to compile a list identifying all families of marine animals that ever existed, carefully noting where they appeared and disappeared...
Within days of the Raup-Sepkoski announcement, word of their work quickly spread to other areas of science. Astronomers leaped into the fray with the greatest zeal, and before long, the race was on to explain one of the most intriguing theories of life on earth...
...debris-filled galaxy takes about 67 million years, and the sun slips through the most crowded region every 33 million years. During this time it could be blocked by the debris. The 33 million-year period corresponds roughly to the 26-million year cycle of extinction postulated by Raup and Sepkoski and the differences between the two figures can be accounted for by uncertainties in astronomical and geological datings, say the originators of the theory, Richard Smothers and Michael Rampino...