by Dawn R. Cole

Created on: April 02, 2009   Last Updated: April 04, 2009

THEORIES ON HOW THE DINOSAURS BECAME EXTINCT

Since the beginning of geological time, the earth has undergone five mass extinctions. The "Big 5" caused the extinction of about 99% of the species that once inhabited the earth. The last major extinction occurred 65 million years ago, somewhere near the end of the Cretaceous and beginning of the Tertiary periods, commonly referred to as the K-T Boundary. This is when the dinosaurs mysteriously disappeared. The K-T extinction, though not the largest, has become the most baffling to scientists and fascinated the general public for years.

The inability to explain what really happened has lead to a multitude of extinction theories. Many of the theories were discarded because they did not account for the fact that some species were completely wiped out and others survived. Some only explained the demise of the larger species, but did not address the smaller animals or marine life that was also affected. Only a few of these theories have been proven to be scientifically viable but even with today's advanced technology, the exact cause of the large invertebrate's demise still remains unknown.

Mass extinctions disrupt the co-dependence of living organisms on Earth and are very complicated processes. They can be triggered by evolutionary issues, environmental and climactic changes, or catastrophic events. All extinction theories have been divided into two main categories:

1. Intrinsic Gradualists = the dinosaur's extinction happened gradually over time, and was earthly in nature.

2. Extrinsic Catastrophists = the extinction was due to a sudden, punctuated event, and was extraterrestrial in nature.

INTRINSIC GRADUALIST THEORIES:

A. Massive Volcanic Activity:

A huge increase in volcanic activity occurred around the same time of the dinosaur's extinction. Excessive volcanic activity would have spewed ash into the atmosphere, blocking the sun's rays, and coated the surrounding habitat with molten lava. Temperature shifts, and decreased or contaminated food and water supplies, would have had a major effect on the dinosaur's ability to survive.

B. Continental Drift/Plate Tectonics:

During the K-T Boundary period, the oceans were regressing from the landmasses. This would have impacted the climate, the food supply, and potentially could have created "land bridges" that allowed predators to invade the dinosaur's territory.

C. Infectious Disease:

Historically, deadly viruses and bacterium have been associated with the decrease in population

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