The first question that must be posed when trying to crack the mystery of the
mass extinction is to ask, throughout history were there any other occurences of
this magnitude? The answer is a resounding yes. Altogether over time there has
been about eight mass extinctions to large land dwelling vertebrates. The most
recent was about ten thousand years ago, killing most of the giant mammals like
mammoths, mastodons, super-large camels, saber-toothed tigers, and others (Bakker
428). The second question, is whether or not these mass extinctions follow a
pattern? Once again the answer is yes. Every time a mass extinction occurs on
the land ecosystem, the oceanic system is hurt. When the dinosaurs died, many
sea animals also died out (Bakker 428-430). The final question to be asked, is
when these mass extinctions occur, are both land and water animals affected, and
if so, are they affected at the same point in time? All saltwater animals
suffered, however, freshwater creatures were left unaffected. Plants on land did
suffer, but not nearly as much as the dinosaurs and other creatures that
depended on them as a food source.(Bakker 431). Since the time that the first
dinosaur was discovered, paleontologists have been pondering the demise of the
dinosaurs. Over a hundred theories have been produced to explain this mass
extinction (Psihoyos 255). The dinosaurs may have died because, "the
weather got too hot," ; "the weather got too cold," ; "the
weather got too dry," ; "the weather got too wet," ; "the
weather became too hot in the summer and too cold in the winter," ;
"the land became too hilly," ; "new kinds of plants evolved which
poisoned all the dinosaurs," ; "new kinds of insects evolved which
spread deadly diseases," ; "new kinds of mammals evolved which
competed for food," ; "new kinds of animals evolved which ate all of
the dinosaurs' eggs," ; "a giant meteor hit the earth," ; "a
supernova exploded near the earth," ; "cosmic rays bombarded the
earth," ; or "massive volcanoes erupted all over the earth at once (Bakker
425)." Scientists' beliefs seem to fall into two basic common positions,
the Catastrophists, and the Gradualists (Psihoyos 255). The Catastrophists
believe that a huge catastrophic event took place, killing all of the dinosaurs.
The most popular theory of the Catastrophists is the asteroid theory. An
asteroid called Chicxulub hit the earth creating a 150 mile wide crater near the
Yucatan Peninsula in Mexico. The date this asteroid hit the earth was sometime
about 65.7 million years ago, just about the time the dinosaurs died (Psihoyos
255). When this two-mile-wide asteroid hit the earth, it probably shattered and
sent tons and tons of asteroid-earth dust into the stratosphere. The lack of
light caused by the dust blocking out the sun would have caused many plants to
die out, leaving plant eating dinosaurs to die, and with no herbivores to hunt,
the carnivorous dinosaurs would die out, the domino effect (Krishtalka 19-20).
This event also would have frozen the earth, another reason why it would kill
all of the dinosaurs. No one can prove this theory, but it is one of the most
recent theories among scientists these days, as to what killed off all of the
dinosaurs. The dinosaurs were around for roughly 140 million years. They were
the ruling beasts of the earth for this whole period. Then, 65 million years ago
the dinosaurs just all died. None flying through the air, none swimming in the
water, none walking on land. They were all just gone. "The death of the
dinosaurs was the biggest mass extinction in the history of the earth (Bates
8-10)." The first clue that led scientists to the asteroid theory was the
finding of a thin layer of clay in the ground. In 1978 Walter Alvarez, a
Professor of geology from Berkeley, California, was driving up out of a deep
limestone gorge behind Gubbio, Italy, when he noticed something strange.
Limestone was formed when little prehistoric sea animals called forams died and
fell to the bottom of the ocean to form rock. When he was driving along he side
of this gorge he noticed that right at one point, all of the forams were gone.
This also happened to be a point in the ground right at 65 million years, right
about the time the dinosaurs died. Another strange thing Alvarez noticed was
that right in between the forams and the above rock was a thin layer of clay. He
felt that the clay might be important so he chipped a piece off, and hid it
away. Upon his arrival back in California he showed the clay to his father, Luis
Alvarez. Together they decided to find out what this clay was doing in the
middle of the rock. To see how long the clay took to form, the measured the
density of iridium, a metal in cosmic dust that the earth collects as it
revolves around the sun. To their amazement, though, the clay contained massive
amounts of iridium. Now they didn't care how long the clay took to form, but why
it contained so much iridium. After a while, they came up with a working theory.
Perhaps a comet or asteroid crashed into the earth. Both of these contain
extremely high amounts of iridium, so it was a perfectly working explanation.
Upon impact this heavenly body would smash into millions of little pieces, fly
into the atmosphere, and cause destruction on the earth (Bates 11-14). This clay
is a marker between the Cretaceous and the Tertiary periods. It is now called
the K-T boundary. When the K-T boundary was looked for in New Zealand and in
Denmark, it was still found. There is another place the iridium could have come
from, and that is the center of the earth. But, unless volcanoes erupted all
over the entire world at once, this is a very unlikely place for it to have come
from. So, with all this in mind, the answer became very clear for Luis and
Walter Alvarez and their colleagues. This clay layer came from outer space (Krishtalka
20-21). Finally, in the early 1990's, researchers found something very exciting.
They had discovered Chicxulub. Chicxulub is a non-volcanic crater buried in the
Gulf of Mexico. This crater is more than a hundred miles across. The size,
structure, and composition of this crater led scientists to believe that
approximately 65 million years ago an asteroid, two miles in diameter, came
flying towards the earth (Horner 208). As scientists look at the K-T boundary,
they noticed something else strange, nowhere on earth can dinosaur remains be
found on or above this line of clay. In fact, the closest any remains have been
found were about nine feet below it. It would be hard for scientists to say
exactly how many years nine feet of earth represents, but it's safe to say it
would be around 100,000 years. Experts who feel an asteroid killed the dinosaurs
say that it just took all of 100,000 years for the dust cloud to resettle to the
ground, and by that time, the dinosaurs were long gone (Horner 211-212). Another
cause, less common, yet still possible, for the extinction of the dinosaurs, is
the “Deccan Trap” thoery. The Deccan Traps was a massive volcanic eruption
that took place just about the time the dinosaurs died. So much lava was spewed
in this eruption that the Himalayan Mountains were formed. Also, though, enough
ash could have been thrown up into the atmosphere in this eruption, that the sun
would have been blocked out, killing the dinosaurs, some plants and other
animals (Psihoyos 255). Researchers are beginning to agree that a catastrophic
event at the end of the Cretaceous caused mass mortality, but not immediate
extinction. This is ironic, however, because for years scientists have tried to
prove this catastrophe caused sudden and rapid extinction. Now that rapid
extinction has been accepted, it turns out it wasn't so rapid after all (Hsü
221). This is exactly what the gradualists believe, that this extinction was
slow. They believe this extinction was brought on by something like climate
changes, smaller volcanic eruptions, rampant spreading of deserts, or the
drainage of inland seas. All of these, however are caused by continental drift.
This is a weak belief, though, because as paleontologist Jim Jensen said,
"Continental drift can be used to explain everything- from lousy weather to
Republicans (Psihoyos 255)." If the dinosaurs died slowly, it would be very
likely that the cause would be more random than a single catastrophic event.
Some members of some groups may be eliminated, but not all members of any one
group. Looking at certain studies, this is what scientists found, a steady
decline in genera of dinosaurs from the oldest (deepest) layers of the column,
to the youngest (Horner 213-214). A column of sediments in North Dakota, "A
detailed breakdown shows that the apparently fixed number of species owes much
to rapid recovery after mass extinctions… Species diversity was drastically
reduced at the end of each geological era, not only at the species level, but
among genera and families too (Hsü 94)." There are also a fair number of
scientists who believe in both kinds of theories. They have called the
combination of events that led up to this extinction, "The worst weekend in
the history of the world (Hsü 95)."