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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. 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
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).
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
when it will happen.
I firmly support Wilson in his analysis that we are in the midst of a sixth extinctionary
phase, which has been brought upon by anthropological causes. Man has systematically
destroyed natural habitat in an eclectic collection of settings. Some he has actively pursued to
destroy for his own odds and ends; the destruction of others he has passively brought about as
human settlements and interference continues unabated. Therefore, it is fair to say, that this
extinctionary phase has been brought about by humans.
Evidence in Favor of Statement
Biodiversity is reduced every time habitat is destroyed. Humans and destroyed habitats
for harvesting of natural resources (example for agriculture) and the principal evidence concerns
these activities. Apart from agriculture, other activities include urban spread, as cities have
magnified several times their sizes in just the past century, mining and logging activities for
construction, trawling etc (Ravenga, Brunner, Henninger, Kassem & Payne, 2000).
Climate Change
The rapidly expanding energy needs of emerging economies and the thrust thus far by
developed ones has implied that there has been a spurt in greenhouse emissions. Oxides of
sulphur, carbon and nitrogen existing in gaseous form have formed a thermal cloak around the
planet preventing the smaller radiation emanating from the earth’s surface from leaving the
planet. At the same time, the smaller wavelength of incoming radiation implies that energy
continues to accumulate; temperatures have thus been rising. Rising sea levels and melting polar
caps, together with the effects El Nino and La Nina have already damaged extensive coastal
ecosystems as islands are being submerged.
Loss of habitat cannot merely be seen as a territorial phenomenon. Instead, human factors
of water pollution and increasing noise pollution are also causing the surroundings to change for
delicate species, unable to adapt to the quick change of pace for them. In any case, this
destruction of habitat has been identified as the main reason behind the extinction of species.
Humans are to blame for a majority of processes within the habitat fragmentation, geological
processes, climate change as discussed above and other invasive actions that deplete the
Examples of Species Affected
Several species have become extinct and more are at risk following weaker carrying
capacities. Almost 82 percent of endangered bird species have encountered their most serious
risk from loss of habitat. Then, endemic organisms, owing to their limited domains, are unable to
continue living away from their homes. An example is the Giant Panda, once found all over in
China, but restricted today to smaller parts in the south-west owing primarily to deforestation.
Islands have suffered from depletion of coastal reefs and thinning of marine life in
general. Among those most affected are New Zealand, Philippines, Madagascar etc. Lack of
governmental oversight and instability in governments have plagued central America and parts
of Africa. In these areas, unsustainable agricultural habits have caused extensive damage to the
native species (Kauffman & Pyke, 2001).
The areas least affected by destruction of habitat have been arid regions and plains.
Degradation has only been seen in about 10 percent of the drylands including savannas,
deciduous forests, grasslands etc. Over 35 percent of the mangroves of the world have also been
destroyed by loss of habitat. However, this trend continues unabated. If there is no prompt
intervention, we are likely to accelerate the rate of loss of species (McKinney, Schoch &
Yonavjak, 2007).

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