The theory is that volcanic activity became so widespread as to cause a severe buildup in gas, ash, and dust to accumulate in the atmosphere to the point that the sun's rays were eventually lessened to the point that temperatures plummeted, plant life died, and the dinosaur could not adapt to their new environment and gradually died off as a result. The physical evidence for this theory is very similar to that offering support for the collision theory and, as a result, many scientists split their opinion between the two theories. There is body of evidence that supports the theory that the emergence of mammals on the earth contributed to the extinction of dinosaur. The appearance of mammals created an environment of competition that the dinosaur had not been forced to encounter before and when mammals began competing for the same food stuff and, more importantly, began seeking dinosaur's eggs the dinosaur were ill-equipped to compete.

It would be nice if the fossil records would support one of the above stated theories over the other but this is not the case. In certain areas of dinosaur discovery, fossil records indicate a sudden extinction as there is virtually no fossil records after a specified...

This divergence may indicate that the extinction occurred for various reasons throughout the areas occupied by dinosaur activity.
The final theory is based upon the idea of continental drift. This theory postulates that the earth's land masses were gradually changed by changes in oceanic activity and a shifting of the continental shelves. The result was that the dinosaurs were unable to adjust to the resulting changes in climate and gradually died off. The strongest evidence for this theory is that fact that ocean levels dropped off severely in the period surrounding the extinction of the dinosaur.

The likelihood is strong, based upon the physical evidence that is available, that a combination of factors led to the extinction of the dinosaur. As no one theory is able to categorically establish why dinosaur became extinct and the physical evidence lends credence to all present theories, the best bet is that portions of all suggested theories contributed and that eventually a new theory will be offered that more accurately explains the reasons. Until then, all available theories merit consideration.

Earth Science