The second step is asking whether or not these mass extinctions follow a pattern. The answer again is yes. Every time a mass extinction occurs on the land ecosystem, the oceanic system is hurt. When the dinosaurs died, many sea animals also died out (Bakker 428-430).

The last step is to observe that the extinctions occurred on both land and water, at the same time, but in different ways. All saltwater animals suffered. Large land animals suffered, but freshwater creatures were left untouched. Plants on land did suffer, but not nearly as much as the dinosaurs and other creatures that ate them (Bakker 431).

Since almost the time that the dinosaurs were discovered paleontologists have been pondering the demise of the dinosaurs. Over a

hundred theories have been produced to explain th

York: Macmillan Publishing Company, 1985.

Evolutionary Saga. New York: HarperCollins Publishers, Inc., 1997.

is mass extinction (Psihoyos 255). The dinosaurs may have died because, "the weather got too hot," ; "the weather got too cold," ; "the weather got too dry," ; "the weather got too wet," ; "the weather became too hot in the summer and too cold in the winter," ; "the land became too hilly," ; "new kinds of plants evolved which poisoned all the dinosaurs," ; "new kinds of insects evolved which spread deadly diseases," ; "new kinds of mammals evolved which competed for food," ; "new kinds of animals evolved which ate all of the dinosaurs' eggs," ; "a giant meteor hit the earth," ; "a supernova exploded near the earth," ; "cosmic rays bombarded the earth," ; or "massive volcanoes erupted all over the earth at once (Bakker 425)." Scientists' beliefs seem to fall into two camps, the Catastrophists, and the gradualists (Psihoyos 255).

Finally, in the early 1990's, researchers found something very exciting. They had discovered Chicxulub. Chicxulub is a non-volcanic crater buried in the Gulf of Mexico. This crater is more than a hundred miles across. The size, structure, and composition of this crater led scientists to believe that approximately 65 million years ago an asteroid, two miles in diameter, came

There are also a fair number of scientists who believe in both kinds of theories. They have called the combination of events that led up to this extinction, "The worst weekend in the history of the world (Hsu 95)."

This is exactly what the gradualists believe, that this extinction was slow. They believe this extinction was brought on by something like climate changes, smaller volcanic eruptions, rampant spreading of deserts, or the drainage of inland seas. All of these, however are caused by continental drift. This is a weak belief, though, because as paleontologist Jim Jensen said, "Continental drift can be used to explain everything- from lousy weather to Republicans (Psihoyos 255)."

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Approximate Pages = 7 (250 words per page double spaced)