The Final Mass Extinction

azambetti's picture

With the human species in a full dominance swing over the world, is the world due for a mass extinction?  At the end of the Cretaceous period, 65 million years ago, an event occurred that would forever change organisms’ interactions amidst the earth’s biota.  For 160 million years, the dinosaurs played the same role that humans are staring in on the present earth.  The question is, when will this reign terminate?

The dinosaurs had 160 million years to completely diversify into over 330 species, and while the animal kingdom was able to radiate into thousands of different species, the one species that has taken control of nearly every ecosystem on this earth is the Homo sapiens.  The anatomically modern human has only been roaming the earth for 200,000 years.  Humans are so homogeneous that they all fit into one species that has very little variation at the chromosomal level.  Therefore, while allegedly, the intensely disparate dinosaurs needed an enormous asteroid to crash into the earth at the Yucatan Peninsula to inevitably end their reign over the earth’s ecosystems, what would need to happen for the same result to happen to an exceptionally homogenous group, whose parasitic relationships have affected every organism on this planet?

Today, a mass extinction event could too easily result from humans’ self-centered behaviors.  A mass extinction event is one in which “a large proportion of the biota is exterminated in a very short time on a geographical scale” (Mayr 201).  While humans have developed an exceptionally high level of intelligence along with imposing technologies, and have become the primary wardens of the world’s aggregates, they also have the sole distinction of being the only species in the history of the earth able to generate a mass extinction event capable of the annihilation of the majority, if not all, of the species on the planet.

Contrary to popular belief, there has been, in the history of the earth, more than just one mass extinction event.  In fact, there have been upwards of nine mass extinction occurrences in the last 439 billion years (Mayr 202).  Five of these events, including the one that exterminated the dinosaurs, eradicated 76-95 percent of the living species inhabiting the earth (Mayr 202).  The earliest was discovered to be about 439 million years ago and was the result of a “drop in sea levels as glaciers formed” and a rise in “sea levels as glaciers melted” (Siegel).  The Ordovician-Silurian extinction, as it was later called, was the second worst extinction event in history. 

The Late Devonian extinction, which occurred 364 million years ago, mainly affected the marine ecosystems, killing “22 percent of marine families” (Siegel).  The impact of the event resulted in the loss of “the major reef-builders including the stromatoporoids, and the rugose, and tabulate corals” (park.org- Devonian).  The cause of the event is unknown.

Following the Late Devonian, was the Permian-Triassic extinction, which was about 251 million years ago.  During the Permian period (286-248 million years ago), for the first time, the “continental area exceeded that of oceanic area” (park.org- Permian), which allowed for the radiation of terrestrial creatures, including insects and reptiles.  The Permian-Triassic extinction was the worst mass extinction event in history.  Many believe it was the result of an asteroid impact that then caused volcanoes to erupt, which resulted in a loss of oxygen in the water masses of the world (Siegel).  The event was responsible for the termination of 95 percent of all species.

From 199 to 214 million years ago, it is suspected that “massive floods of lava erupting from the central Atlantic magmatic province -- an event that triggered the opening of the Atlantic Ocean” caused “volcanism [that] may have led to deadly global warming” (Siegel).  This event, known as the End Triassic extinction, was responsible for the demise of 22 percent of marine life and 52 percent of marine genera (Siegel). 

And finally the most famous of the five worst mass extinction events of the earth occurred about 65 million years ago, the Cretaceous-Tertiary extinction.  Besides the annihilation of one of the most successful groups of creatures, the dinosaurs, this event also resulted in the destruction of “16 percent of marine families, 47 percent of marine genera and 18 percent of land vertebrate families, including the dinosaurs” (Siegel).

Unfortunately, the devastation brought by these five major earth altering events will not come close to the amount of destruction projected with the termination of the Holocene.  The Holocene represents the last 10,000 years of human reign over the world’s environments, which are plagued with pollution, deforestation and rampant overuse of the earth’s ever- deteriorating resources.  Every past mass extinction event, except the Holocene, has been the result of an asteroid impact or major climate change.  “Because the rate of this extinction event appears to be much more rapid than the "Big Five" mass extinctions, it is also known as the Sixth Extinction” (Wikipedia).  Humans are the sole contributors to the ever worsening condition of the earth.  Interestingly, humans are not the only organisms able to significantly change the composition of ecosystems and the atmosphere.  Possibly the simplest example is that of the cyanobacteria. 

3.8 billion years ago, the simplest of bacteria, all of which are prokaryotes, were able to generate from an environment containing no other organisms.  Because of the cyanobacteria, the earth’s environment was converted from a methane atmosphere, not containing oxygen, to one that did contain oxygen, as a result of cyanobacteria’s cellular respiration.  Organisms were then able to evolve into a variety of multicellular organisms.  Starting 3.8 billion years ago, one could say that the cyanobacteria created and supported the evolution of an enormously diversified planet. While there are a plethora of other examples of one or another species causing positive or negative effects on an ecosystem, humans have the distinction of being able to change the course of history by willfully choosing to implement drastic environmental and planet-wide behaviors that could prevent the mass annihilation of the majority of earth’s living things.  Unlike all other mass extinctions, a choice has been given to the reigning species.

    Works Cited 

“Holocene extinction event.”  Wikipedia, The Free Encyclopedia.  2007.  Feb 14, 2007.  <http://en.wikipedia.org/wiki/Holocene_extinction_event>. 

“Mass Extinction of the Phanerozoic Menu.”  Extinctions: Cycles of Life and Death Through Time.  Feb 14, 2007.  <http://park.org/Canada/Museum/extinction/extincmenu.html>. 

Mayr, Ernst.  What Evolution Is.  New York: Basic Books, 2001.

Siegel, Lee.  “The Five Worst Extinctions in Earth’s History.”  Space.com.  Sept 7, 2000.Feb 14, 2007. <http://www.space.com/scienceastronomy/planetearth/extinction_sidebar_000907.html>.

  

Comments

Anne Dalke's picture

pushing back

2/17/07

Andrea—

I enjoyed reading your first paper: it taught me a lot (always my main interest in this activity!): I didn’t know about the five mass extinctions, and was instructed by your account of the causes and extinct of each. Thanks for that—

Here are my pushing-back remarks and questions:

--what’s the central question of the paper? (you begin with 3: Is the world due for another extinction? When will the human reign terminate? What will need to happen for this result?) I think the first one is rhetorical (so why phrase it as a question? For the rhetorical effect? Because a question works better—why?—than a claim?) I think the second is unpredictable (or is it? See “An Inconvenient Truth”; but you don’t address this). And the third…I’m not sure…does the catalogue of past extinctions address that question? Or is that (again, very interesting) catalogue actually only obliquely related to any of your questions?

You’ll see that I have a couple of factual questions for you (is “parasitic” the technically accurate word for our relations w/ other organisms? Are we really the “sole contributors” to the ever-worsening condition of the earth?—what about “natural” occurrences like volcanic eruptions, tsumanis, etc.?)

But my really big questions are about consequences and perspective. You end in a very bad place, of course. How to go forward from here? Once you’ve shown how close the doomsday clock is to imploding…what is there to do? What space have you given your reader to move into? Is your paper intended to have the same effect as Gore’s movie (which made me feel very bleak and very hopeless)? What did you hope to accomplish with this paper? What reaction did you want to evoke?

Finally: I know we talked about perspective AFTER you had written the paper, so this is just to initiate a conversation about what difference it would have made—or could make in your next one. Your perspective here is that of a human who thinks it “unfortunate” that the human-caused extinction will outdo all earlier ones. “Would that be a tragedy?” “Does it depend on your point of view?” What if you wrote as a student of evolution (as you are): mightn’t the destruction caused by humans, like the destruction that wiped out the dinosaurs, clear the earth/create some space for the evolution of new organisms?

Anne

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