Dunnit to the Dinosaurs?
an asteroid impact bring the dinosaurs to extinction?(Copyright
Lee, Krystek, 2008)
reigned over the earth for more than 100 million years and suddenly,
mysteriously disappeared. What caused the demise of this ubiquitous
group of reptiles which included some of the largest animals to
ever walk the planet?
One of the great mysteries in science is the extinction
of the dinosaurs at the end of the Mesozoic era some 65 million
years ago. Who (or more likely what) caused it is unknown and
a subject of great debate.
Dinosaurs appeared at the beginning of the Mesozoic
era and were the dominant form of life for the next 140 million
years. They lived almost everywhere there was land including Antarctica.
We can see their bones in the geological record laid down over
time. The lower stratum of rock contains the earliest and most
primitive species of dinosaur, and the upper stratum contains
the newer species. Then, suddenly, at a geological strata line
called the Cretaceous-Tertiary boundary (often referred to as
the K-T Boundary), the dinosaurs disappear.
In fact, not only do the dinosaurs disappear, many
other species do too. In the sea, the great marine reptiles, like
the plesiosaur, the mososaurs and the ichthyosaur vanished. Nearly
half of all invertebrate ocean organisms, (including ammonite
cephalopods which had been around for 325 million years) were
gone. In the sky, the great flying reptiles also disappeared.
Scientists believe that climatic changes might
be responsible for most of these extinctions. There is evidence
that shows the temperature dropped at the end of the Mesozoic
and the sea levels fell. Such a sudden change in temperature might
have affected the growth of plants which were at the root of the
dinosaur's food chain.
Some of the theories proposed for dinosaur extinction
-Cosmic radiation from a nearby exploding supernova
star killed them.
-Acid rain from volcano activity was responsible.
-Continental drift altered the climate.
-Disease ravaged dinosaur populations.
-Small mammals appeared that fed on dinosaur eggs.
asteroid, similar to this one, may have been responsible
for the death of the dinosaurs. (Nasa)
One of the most well-known and intriguing theories
suggested for dinosaur extinction is the asteroid theory. In the
1980's the father-son team of Luis and Walter Alvarez discovered
a layer of iridium in the K-T boundary. Iridium is rare on earth,
but abundant in meteorites. The Alvarezs' suggested that a huge
asteroid or comet, perhaps miles in diameter, hit the Earth at
that time. The result of such an impact would be an enormous explosion
that would throw dust clouds into the sky, darkening the planet.
Massive forest fires, triggered by the hit, would add smoke to
the sky. This would cool the planet causing the climatic changes
A crater, now worn down and partly under the ocean,
was found along the Mexican Yucatan Peninsula and its creation
coincides nicely with the K-T boundary. NASA scientists estimate
that the asteroid that made Chicxulub Crater, as it is now known,
would have been about 6 to 12 miles in diameter. The crater is
about 130 miles across.
Scientists at the Southwest Research Institute in
Boulder, Colorado, have even been able to trace the path of that
asteroid back into space. According to their calculations 160
million years ago a collision between a 100-mile-wide asteroid,
named Baptistina, and a smaller unnamed asteroid out beyond
the orbit of Mars, shattered the larger object and sent pieces
of it into the inner solar system. Ninty-five million years after
that these pieces encountered earth, ending the dinosaurs' reign.
Not a Bang
Not all scientists are satisfied with the asteroid
theory, however. They point out the fossil record shows the dinosaurs
were already in decline before the K-T boundary and the asteroid
might just have been the final blow that finished off a population
already weakened by some other factor.
In Montana, at a dig supervised by celebrated paleontologist
Jack Horner, Nan Crystal Arens from Hobart and Smith Colleges
carefully examined the fossil leaves and pollen from a slice of
the Hell Creek formation at many different levels. The Hell Creek
formation is set just above the K-T boundary and represents the
millions of years just before the extinction of the dinosaurs.
Dr. Arens found that the number of different species of plants,
especially flowering plants, declined significantly as one got
closer to the boundary. Perhaps 90% of all the flowering plants
had already died before the asteroid struck. Since these represented
a large portion of the herbivore dinosaur's food supply, and herbivore
dinosaurs were in turn food for the carnivores, this might have
caused a sharp decline in dinosaur populations even before the
Deccan Traps Volcanos
Some scientists suspect that volcanic activity may
have caused the dinosaurs' demise. In the several million years
preceding the extinction event, volcanoes in what is now India
were extremely active. While the span of the eruptions originally
seemed too long to explain such a rapid extinction event, recent
tests have shown the largest of the eruptions associated with
the massive Deccan Traps lava beds in India; coincide with the
K-T Boundary. During this period as much as two-thirds of the
lava beds were created, covering nearly a million square kilometers
(about half the size of modern India). According to volcanologist
Vincent Courtillot, these eruptions might have released 10 times
more climate-altering gases and materials into the air than the
meteor impact in the Yucatan. These would have included dust and
sulphuric particles that would have blocked sunlight cooling the
planet. Carbon dioxide, a greenhouse gas, was also released by
the volcanos and would have heated up the earth once the dust
cleared from the skies leading to an enormous temperature swing.
examining insects trapped in amber in ancient times scientists
can understand the types of diseases the dinosaurs faced.
Other scientists think that some of the smallest
animals may have been responsible for bringing an end to some
of the largest. George Poinar, a professor of zoology at Oregon
State University, believes that during the late cretaceous the
number of insects and the number of insect species rapidly expanded.
Many of these species were biting insects that carried new diseases.
Poinar and his wife have examined many of these bugs from that
era that have been preserved in amber and found evidence that
they carried forms of leishmania and malaria that could infect
reptiles. They also examined fossilized dinosaur dung finding
nematodes, trematodes and protozoa that might have given the animals
dysentery. The dinosaurs probably got these intestinal parasites
from insects that had been visiting dung piles and then transferred
them on to the dinosaurs food.
Poinar argues that the high temperatures and the
recent evolution of flowering plants would have made the late
cretaceous perfect conditions for an explosion in the number of
insects and the illnesses they carried. The dinosaurs, which would
have had little resistance to these new diseases, would have declined
Double Whammy Theory
It may be that the dinosaurs were not just the victim
of a single event, but a string of bad luck. Professor Arens has
carefully looked at this idea and has attempted to measure the
extinction rate of species during periods when there were major
asteroid impacts, periods of massive volcanic eruptions and periods
when neither were happening. Surprisingly, the rate of extinction
for each type of period is about the same. What she discovered,
however, is that during periods when both massive volcanic eruptions
and impacts were taking place at the same time extinction
rate climbs. This suggests that no single disaster event might
cause mass extinctions, but a combination of two or more are needed
for it to happen, hitting life on earth with a "double whammy."
The fossil record shows that the mass extinction
that killed the dinosaurs wasn't the only one that has occurred
in our planet's history. The earth has suffered a number of such
traumatic events over its life. In fact the K-T extinction wasn't
even the largest. The Permian-Triassic (P-Tr) extinction event,
sometimes referred to as the Great Dying, occurred about
250 million years ago and eliminated 90 percent of known species
from the planet. As with the K-T extinction, nobody is quite sure
what caused this disaster.
They All Dead?
Did any of the dinosaurs survive the extinction?
Scientists have very rarely found bones of dinosaurs buried above
the K-T Boundary. A single Hadrosaur leg bone found in
the San Juan Basin, New Mexico, might suggest that a small population
of these dinosaurs survived as long as a half a million years
into the following Paleocene era. However, it is also possible
that the fossils in question, which are very few in number, were
unearthed by some geologic event, then reburied at a higher level.
Occasionally stories still appear about dinosaurs
being found still alive today in some remote location of the world
(for example, the legend of mok'ele-mbembe
in Africa). While there are several famous fictional books like
Arthur Conan-Doyle's The
Lost World on this subject, there is no hard evidence
that any dinosaur, other than the birds, their avian decedents,
have survived into modern times.
It is likely scientists will continue to puzzle
over the death of the dinosaurs for many years to come. Part of
the mystery of K-T extinction is why certain species died out
while others survived. Mososaurs went extinct while other marine
reptiles, like crocodiles, are still around. If climate change
is responsible why did the dinosaurs, hearty creatures that lived
in all kinds of conditions all over the planet, die when frogs,
who are much more sensitive to temperature change, still survive
Barringer Meteor Cater in Arizona though impressive, is
only about a mile wide. Just a fraction of the 130 mile
wide crater left by the asteroid that ended the Mesozoic
Era. (Copyright Lee Krystek, 2008).
New Theory of Mass Extinction Sheds Light on
Earth's Cataclysmic Past, Hobart and Smith Colleges Website,
October 24, 2006, http://web.hws.edu/news/update/showrelease.asp?id=24681
What Bugged The Dinosaurs? Insects, Disease
And Death In The Cretaceous, by George, Jr. Poinar and Roberta
Poinar , Princeton University Press, 2008.
Dinosaur Deaths Outsourced to India?, The
Geological Society of America Website, October 2007, http://www.geosociety.org/news/pr/07-59.htm
Copyright Lee Krystek 1996-2008.
All Rights Reserved.