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The Mass Extinction Controversy
| Article
# : |
14174 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
1 / 1988 |
3,526 Words |
| Author
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Marc J. Defant
Marc J. Defant is professor of geology at the University of
South Florida. He specializes in the study of volcanoes and is
the author of Voyage of Discovery: From the Big Bang to the
Ice Ages, a panoramic history of the universe, including our
galaxy, solar system, and planet. |
Imagine an explosion that would equal the simultaneous detonation of 100 million one-megaton nuclear warheads--10,000 times the existing worldwide nuclear arsenal. The energy released from such an incredible explosion would be equivalent to that released from a massive meteorite, called a bolide, that may have struck the earth some 65 million years ago. The diameter of the bolide was probably greater than the height of the highest mountain on earth. The material blown into the atmosphere from the collision, in the form of a dust cloud, would have quickly encircled the globe and taken months to settle. During that period of settling, the sunlight would have been drastically reduced and the photosynthetic processes in plant life would have been arrested, resulting in a tremendous number of extinctions. Higher life forms, such as the dinosaurs, dependent on large intakes of food, would have been particularly threatened, and a large number of species would have disappeared.
Grist for the science fiction writer? Perhaps, but an increasing number of the world's top scientists believe that this scenario may have contributed to the disappearance of the dinosaurs and several other major groups of animals and plants that became extinct at the end of the Cretaceous and the beginning of the Tertiary time periods.
Geologists have been aware for more than a century of the unique and dramatic change in the rock record representing the boundary between the Cretaceous and Tertiary time periods, referred to as the K/T boundary. An abrupt decline in the number of fossils in rock directly above the K/T boundary compared with abundant fossil remains in rock directly below has been noted wherever the boundary has been observed, encompassing sediments from as far south as the tip of Argentina to as far north as the arctic of Canada. Even more impressive is the observation that many species, including all the dinosaurs, marine and flying reptiles, ammonites, and a large number of corals, gastropods, and echinoids, met almost instantaneous extinction, geologically speaking--perhaps within a 100,000-year interval. These were not the only life forms to be annihilated. The tiny, one-celled coccolithophorids and foraminifera--creatures that lived in the surface waters of the sea and whose small shells are preserved ubiquitously in the geologic record--suffered almost complete extinction. D.A. Russell of the Paleobiology Division of the National Museum of Natural Sciences in Ottawa, Canada, has postulated that a 75 percent reduction in the diversity of species may have occurred during this geologic episode. Geologists also know that the extinctions occurred over a very short interval of time, and some believe the extinctions were almost
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