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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
Starvation
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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