Essay/Term paper: Extinction of dinosaurs
Essay, term paper, research paper: Biology
Extinction of Dinosaurs
Two-hundred and thirty million years ago the first dinosaur-like
creature roamed the earth. Within five million years it could be considered a
dinosaur. They were soon at the top of the food chain. They populated every
continent. Then 65 million years ago they vanished. The most powerful
creatures ever to live on earth had become extinct.
Dinosaurs were not the only victims of this "mass extinction." There
were many other species that were killed off. During what is known as the K-T
extinction (K stands for Cretaceous, T stands for Tertiary), many species and
families became extinct. These include all marine reptiles such as plesiosaurs,
mosasaurs, ichthyosaurs, and ammonites, swimming and flying reptiles, sea
crocodiles, and foraminifera. In addition to that there were many bony fish,
sponges, snails, clams, and sea urchins became extinct.
Paleontologists have proposed scenarios that could have caused these
extinctions. One such scenario involves the growing number of small mammals
which ate dinosaur eggs, and therefore caused the dinosaurs' birth rate to drop.
The birth rate became smaller than the death rate and the dinosaurs died out.
This, however, is not a plausible scenario. This would only account for the
dinosaurs, but not all the other creatures of that time. Paleontologists needed
to come up with a more plausible and devastating theory that would include the
other creatures that died out 65 million years ago.
There have been several major theories that have come about that can all
be substantiated. Any one of these events, theorized by paleontologists, could
have brought an end to the dinosaurs and all the other species that died with
them. Since there are many theories about this I will not write about them all.
I have chosen the theory about death by Cosmic Collision (an asteroid).
In 1980 Luis Alvarez and John Sepkowski Jr., famous geologists, blamed
the extinction of the dinosaurs on a large celestial body which hit the Earth 65
million years ago. According to them, an asteroid five miles across blasted
through the Earth's crust, and threw up molten rock, ash, and dust. Adding to
the support to this theory is the discovery of a layer of iridium in New Zealand,
Denmark, and Italy. This layer became known as the iridium anomaly. Remarkably,
this layer of iridium was found in sedimen tary rock that is abundant on other
celestial bodies. This was too remarkable to be a coincidence, so the research
team decided that the layer of iridium must have been caused by space debris
which resulted from the collision of Earth and another celestial body. At first,
Alvarez's theory was not widely accepted, but as more iridium was found from
that period of time around the world, it became the leading theory. Other
evidence includes the discovery of stishovite, a mineral created by high heat
and pressure. These two minerals were most likely caused by a cosmic collision.
Even more stunning, geologists have found a huge crater on the Yucatan Peninsula
which is dated to be exactly 65 million years old.
Whatever hit the Earth would have caused extreme and immediate havoc,
includ ing, a blast wave which would have incinerated everything in its path.
Tsunamis would occur in oceans all over the world and would affect vast areas.
Water and rock would evaporate. The impact of the asteroid would cause massive
earthquakes all over the Earth, and these earthquakes would increase volcanic
activity. The power of the collision would have also caused global wildfires.
Scientists have discovered large quantities of sulfur around the crater at the
Yucatan Peninsula. When the asteroid or comet hit, it would have mixed with
water to form sulfuric acid, which would have created a barrier to block out
light and heat from the sun. This could have lasted for decades. This cloud of
darkness would have killed off vegetation, and then herbivores, having nothing
to eat, would have died. With no herbivores to eat, carnivores would have
killed each other, and the reign of the dinosaurs would have ended.
Now Alvarez's theory is regarded as one of the leading theories justifying
the K-T extinct
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