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Extinction of the Dinosaurs
This is perhaps the greatest controversy surrounding the dinosaurs. The various theories of the extinction of dinosaurs have only one thing in common: the fact that, except for birds, dinosaurs died out completely and suddenly 66 million years ago, after having been very successful animals for about 160 million years. (In contrast, man's family dates back only four million years.) Each theory has something to recommend it; each theory has its critics.

The geologic moment when dinosaurs died out is known as the K-T Boundary. The "K" stands for Cretaceous (C having already been used for Carboniferous); the "T" stands for Tertiary Period, when mammals began their rise to dominance.

“Geologic moment” is a relative term; in this case, it might mean hundreds of thousands of years. In other words, the dinosaurs died out “suddenly” only in the sense that they had already been around for 160 million years.

Some of the theories proposed for the mass extinction are:

Changing Climates
Greenhouse Effect
Excessive Size
Disease and Epidemic
Egg Predation
Non-viable Eggs
Ecological Replacement by Mammals
Reversal in the Earth's Magnetic Field
Supernova in Nearby Space

The theory that has gained wide acceptance today is that a meteor (or meteors) collided with Earth. A large meteor striking the Earth could have ejected enough dust and debris that blocked sunlight long enough to alter the Earth's climate and cause the prehistoric equivalent of a “nuclear winter.” In a sort of domino effect, some plants would have died out, then the herbivores that ate them, and finally, the carnivores that fed on the herbivores. The changes in ecology may have happened swiftly enough -- in geologic time, of course -- to thwart the mechanism of evolution. That is, the dinosaurs couldn't evolve to meet the new conditions.

The meteor which may have been ultimately responsible for the extinction of the dinosaurs was probably on the order of 6 to 12 miles (10 - 19 km) across. The crater it created off the coast of the Yucatan peninsula 65 million years ago is 120 miles (193 km) in diameter. The force of its impact initially sprayed molten rock and debris worldwide; vaporized minerals thrown into the upper atmosphere took months or years to settle. Known as the Chicxulub Crater, it was discovered using instruments that sense gravitational anomalies.

Double Jeopardy
A theory recently advanced by a team of scientists at Sandia National Laboratories proposes a double engine of destruction: an asteroid impact that may have set off massive volcanic eruptions on the opposite side of the Earth from the impact. The combination of rock dust and debris from the impact combined with volcanic ash may have cast a worldwide pall that killed off many plants and animals.

Antipodal volcanism, the term used to describe this theory, has been studied on Mars where the largest impact basin, Helles Plenitia, is anitipodal (opposite) to Alba Patera, the largest volcano yet discovered in the solar system. Scientists at Sandia have simulated the damage an asteroid six miles (9.7 km) in diameter and traveling at 45,000 mph (72,405 km/hr) would have caused -- a colossal crater more than 15 miles (24.1 km) deep. The shock waves, rippling through the Earth, would take about 80 minutes to travel to the antipode, creating a pipeline of destruction from the depths of the Earth to the surface. It is theorized that a huge eruption, in what is now India, created the great lava fields known as the Deccan Traps about 65 million years ago. However, the antipode to the Deccan Traps is not in the vicinity of the great Chicxulub crater, but rather it is located in what is now the eastern Pacific Ocean where the seabed bears evidence of a major impact. Perhaps, as some experts suggest, two or more meteors struck the Earth simultaneously.

Unfortunately, we still have the problem of the pesky frogs, crocodiles, turtles, marine species, and mammals that survived. Why were they resistant to the meteor-induced changes and not the dinosaurs?

We may one day know for certain what happened to the dinosaurs, but until then only one thing is certain -- that theories explaining the extinction of the dinosaurs will continue to be proposed and argued.

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