by David Thackston

Created on: April 13, 2009   Last Updated: April 21, 2009

While it is known that a major event would have been required to bring about the extinction of dinosaurs, there are several theories about what completely killed them off. Although most scientists agree that a large asteroid did in fact hit the earth around the time of the extinction, there is some disagreement as to whether or not that is the only factor to consider regarding the dissapearance of dinosaurs. Throughout the Paleozoic and Mesozoic era's there were multiple extinction periods, but none were as devastating to the earth's population as the one that occurred sixty-five million years ago. This global extinction, referred to as the Cretaceous-Tertiary event, or the K-T event for short, gave rise to mammals and man, and changed the earth forever. The K-T event spelled the end of the dinosaur era and ushered in the age of mammals, although theories regarding the details of the widespread extinction itself are relatively new. Currently the most popular theory is that a major asteroid impact caused the extinction of the dinosaurs, but there are many other theories regarding their fate.

There are many known factors that could and have caused extinctions in the past. One of the most plausible theories regarding the extinction of dinosaurs was that there could have been a massive epidemic that spread amongst the animals. This could have been a viral or bacterial epidemic that sickened the creatures slowly, or perhaps it was terminal from the onset. It is also possible that migration brought creatures from other areas into contact with one another after long periods of having been isolated. During the cretaceous period many of the remaining dinosaurs were coming into contact with one another for the first time after having evolved in their own confined regions. Renewed contact among isolated species could have exposed all of them to illnesses and parasites that their immune systems were not equipped to handle.

Another theory is that the extinction of the dinosaurs was caused by ozone depletion. This doesn't mean that oxygen dissipated from the planet all together, but that enough of the ozone layer was effected as to eliminate the protection it offers life on earth against ultraviolet radiation from the sun. The massive tectonic activity of the ancient world, combined with the widespread volcanic activity could have reduced the ozone layer quite significantly by releasing gases into the atmosphere. Dinosaurs would have been highly susceptible to this danger,

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