by Brenda Nelson

Created on: April 06, 2009   Last Updated: April 15, 2009

What killed the biggest beasts that ever walked this land? How could something live for so many millions of years (more than 160 million years), then suddenly vanish forever? What really killed the dinosaurs?

These are questions science is still trying to solve. Although we have pieces, and hunches, we truly do not have all the answers. For one thing, it was not one single event that resulted in the death of all the dinosaurs. There were several mass extinctions (at least five) that occurred at different times, marking the end of one period of time, and ushering in a new one. The final extinction event was 65 million years ago, and killed not only the dinosaurs, but most other life on the planet at that time.

There are many theories as to what caused these extinctions, below are the six most likely scenarios.

Asteroid

The most common theory is that the last extinction was caused by an Asteroid that impacted the earth in the area that is now the Gulf of Mexico. This is often referred to as the KT Asteroid. The result of a roughly 6 mile wide (10 km) asteroid hitting the earth would have caused massive problems for life on the planet. The sun would have been obscured by dust particles for months, killing plants and the animals that ate them, in turn animals who fed on those animals would have perished. The impact would have also resulted in tidal waves, acid rain, and probably forest fires. Water would have been tainted with falling particles, and survival of many animals would have come to a halt. Evidence for this has been found in the form of a layer of sediment (called the K-T layer)which has turned up all over the globe from the same time period. Perhaps other asteroids caused other earlier periods of extinction.

Climate Change

As the Cretaceous period came to a close 65 million years ago, we saw mostly tropical plants, with the later Tertiary period plant life had changed. As such it is believed that global temperature fluctuations were beginning to occur and some animals just could not keep up. Certain plants would have died, and plant eaters would have been left without food, then too, the meat eaters. Indeed plankton have been shown to have decreased in numbers around this time, clearly cutting the food supply of marine animals. One interesting note about the climate change theory is that it not only allowed for the survival of the furry mammals, but possibly the survival of a few species of dinosaurs whose bodies had been experimenting with the development

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