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ALTERNATING EXTINCTION & RADIATIONS
Throughout the history of time, the earth has experienced periods where species have
disappeared, while other periods where they have flourished. These periods of alternating
extinctions and radiations are known most commonly in association with dinosaurs, but there
have been many such periods during the existence of planet earth. In fact, this cycle has been
seen on five separate occasions. Five of the major extinction events include End-Ordovician,
Late Devonian, End-Permian, End-Triassic, and End-Cretaceous (Hallam, and Wignall, 2002).
Each of these events realized the end of a species and a time or period that was known on earth.
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Each of these events resulted in life ending and species no long existing. While each of
these events were monumental, the most commonly known, or discussed, extinction event is the
End-Cretaceous. This event was caused by a large asteroid collided with the earth. However, it
was not the collision itself which caused the extinction of the dinosaurs. Instead, rather, it was
the changes to the climate that were the result of the collision. While a species may evolve and
adapt to function within their changing environment, there will come a time when the climate
changes at a rate faster than a species can evolve. This has been the primary reason or force
behind species becoming extinct. Such is the cause with the commonly discussed dinosaurs. As
the environment and climate rapidly changed, the evolution of the dinosaurs was unable to occur
quickly enough, thus resulting in their eventual extinction.
It is believed that these extinction events could have each been caused by space matter,
such as asteroids and meteorites struck the earth, creating a change in climate. Regardless of
whether or not this theory is true, the final conclusion is that severe climate change led to
conditions in which the life of the species could no longer be sustained. For instance, it is believe
that coral could have become extinct from a meteorite striking the earth and causing a dust cloud
ALTERNATING EXTINCTION & RADIATIONS
so large that it led to darkness and plunging temperatures. While the water would have protected
to coral form the dust for the most part, the coral could not adapt to the cooler temperatures and
therefore became extinct (Cook, 2010).
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Not only has it been found that climate change is a key factor in the alternating
extinctions and radiations, it has also been found that changes to the CO2 found within the
atmosphere contribute to the process. CO2 will likely change and fluctuate over time. However,
where there is a sudden increase in CO2, the surrounding environment and species found within
the environment will not be able to survive the drastic changes within their atmosphere. If a
species is not affected directly, the CO2 can affect the water supply. As many species rely upon
water, any increased levels of acid in water will be directly transferred to those species that
consume the water. This increases the level of exposure to the abundance of CO2. With the rapid
increase of this compound, species are unable to evolve quickly enough and thus become extinct.
The pattern of alternating extinctions and radiations cannot be considered without
looking at periods of radiation as well. While periods of extinction have been contributed to
climate change and increased levels of CO2 in the atmosphere, periods of radiation occur when
the atmosphere has a chemical makeup, which supports and sustains the life of a species. As long
as conditions are favorable, a species will be able to thrive and thus radiation of a species will
continue and the species will flourish.
This leads us to question the quote by E.O. Wilson. The discussion of climate change has
come into the mainstream, and is one that must be taken seriously taking into consideration past
extinction events. With the actions of humans rapidly increasing the CO2 found in the
atmosphere, the question of an upcoming extinction event is not if it will happen, but rather
ALTERNATING EXTINCTION & RADIATIONS
when it will happen.
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