The Sixth Extinction

I want to apologize for the double posting. The first time I posted, I noticed that all of my images were lost. Dr. Oliver kindly posted for me and then I noticed that my citations were lost. So I have posted this time and manually added the images.  Hopefully, you will see the entire post with images and citations this time.

            

Human beings were not present when the following five mass extinctions occurred. As you review them you can see that climate change was a potential cause of several of them.

All information below is taken directly from - http://www.bbc.co.uk/nature/extinction_events

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Big Five mass extinction events

Although the Cretaceous-Tertiary (or K-T) extinction event is the most well-known because it wiped out the dinosaurs, a series of other mass extinction events has occurred throughout the history of the Earth, some even more devastating than K-T. Mass extinctions are periods in Earth's history when abnormally large numbers of species die out simultaneously or within a limited time frame. The most severe occurred at the end of the Permian period when 96% of all species perished. This along with K-T are two of the Big Five mass extinctions, each of which wiped out at least half of all species. Many smaller scale mass extinctions have occurred, indeed the disappearance of many animals and plants at the hands of man in prehistoric, historic and modern times will eventually show up in the fossil record as mass extinctions.

Possible causes of this event

Earth's climate is not constant. Over geological time, the Earth's dominant climate has gone from ice age to tropical heat and from steamy jungles to searing deserts.

 Possible causes of this event

Impact events, proposed as causes of mass extinction, are when the planet is struck by a comet or meteor large enough to create a huge shockwave felt around the globe. Widespread dust and debris rain down, disrupting the climate and causing extinction on a global, rather than local, scale.

 Possible causes of this event

Catastrophic methane release

Flood basalt eruptions

Climate change

Impact events.

What was killed by this event

Merostomata

    Sea scorpions

Trilobites

 Possible causes of this event

Flood basalt eruptions

Climate change

Impact events

What was killed by this event

Reptiles

   Postosuchus

Synapsids

   Placerias

The Cretaceous-Tertiary mass extinction - also known as the K/T extinction - is famed for the death of the dinosaurs. However, many other organisms perished at the end of the Cretaceous including the ammonites, many flowering plants and the last of the pterosaurs.

Possible causes of this event

Flood basalt eruptions

Impact events

What was killed by this event

Reptiles

Ankylosaurs, armoured dinosaurs, bird-hipped dinosaurs, ceropod dinosaurs, duck-billed dinosaurs, horned dinosaurs, triceratops, dromaeosaurs, lizard-hipped dinosaurs, nothronvchus, sauropod dinosaurs, sauropodomorph dinosaurs, therizinosaurus, theropod dinosaurs, tyrannosaurs, tyrannosaurus rex, plesiosauria, plesiosaurs, pliosaurs, hatzegoptervx, pterosaurs, and dinosaurs.

Cephalopods

                Ammonites[1]

    

      As you noted above, the Cretaceous-Tertiary mass extinction occurred about 65 million years ago and hominins have only been estimated to be on earth for around 4.5 million years – Australopithecus afarensis, 1.9 million years – Homo erectus, 200,000 – 40,000 – Homo sapiens, our immediate ancestors.[2] Around 5,000 years ago, “humans begin to cast and use metals and build the pyramids.”[3] Human groups were still for the most part hunter-gatherers and early agricultural societies. In 1712, the Industrial Revolution began when “Thomas Newcomen patents the atmospheric steam engine.”[4] In the span of 100 years, “between 1900 and 2000 the increase in world population was three times greater than the entire previous history of humanity– an increase from 1.5 to 6.1 billion in just 100 years.”[5]

As Kolbert relates in The Sixth Extinction, our species was “not particularly swift or strong or fertile,” but “they cross rivers, plateaus, mountain ranges…gather shellfish…hunt mammals,” and “reproduce at an unprecedented rate.”[6] She describes the population explosion, “In a single century the population doubles; then it doubles again and then again. Vast forests are razed. Humans do this deliberately, in order to feed themselves. Less deliberately, they shift organisms from one continent to another, reassembling the biosphere,” and once they discover, “subterranean reserves of energy, humans begin to change the composition of the atmosphere.”[7] This is the status of our biosphere today and while it may be premature to speculate on the final outcome, Kolbert offers us several examples to consider on whether we are heading toward a sixth extinction that we as humans have created.

Golden frogs from El Valle de Antón were so plentiful a decade ago that any walker could spot them easily along any water bank. Today, the few that are alive are carefully sequestered in aquariums with highly restricted access. Amphibians have existed for a couple of hundred million years and now globally within the last fifty years, whole species are now extinct. The causative agent is the chytrid fungi that, “interferes with frogs’ ability to take up critical electrolytes through their skin. This causes them to suffer what is, in effect, a heart attack.”[8] How is the fungi so ubiquitous? As humans travelled around the world, they carried spores of the fungi on them and once the fungi reached a new environment, they thrived to the detriment of the frogs.

From a not too distant past, it is difficult to imagine that the mastodon roamed in North American until about 11, 000 years ago. “Extinction finally emerged as a concept, probably not coincidentally, in revolutionary France. It did so largely thanks to one animal, the creature now call the American mastodon, or Mammut americanum, and one man, the naturalist Jean-Léopold Nicolas-Frédéric Cuvier.”[9] The first mastodon bones were found in New York.

Thomas Jefferson even commented on the various theories of where it came from and whether it was still around. “Such is the economy of nature, that no instance can be produced of her having permitted any one race of her animals to become extinct; of her having formed any link in her great work so weak as to be broken.”[10] How wrong he was. What caused the mastodon to become extinct? “In fact, the American mastodon vanished around thirteen thousand years ago. Its demise was part of a wave of disappearances that has come to be known as the megafauna extinction. This wave coincided with the spread of modern humans and, increasingly, is understood to have been a result of it.”[11]

The great auk once considered related to penguins “ranged from Norway over to Newfoundland and from Italy to Florida, and its population probably numbered in the millions.”[12]

Their extinction can be blamed solely on human beings who took advantage of the ease of killing them to use them for food and for their feathers. Sadly the last two alive were killed simply to satisfy the urges of a collector.   

In the little town of Gubbio, Italy, the key exists for understanding the devastation of a meteoric impact. There, Walter Alvarez was studying how “the Italian peninsula had come into being.”[13] He would discover something that would alter the way extinction had been viewed from one of a gradual nature to one of cataclysmic origin. As he examined the rock formations, his assistant pointed out “a curious sequence…a layer of clay about half an inch thick.”[14] Below it there were certain types of foraminifera, within it, none, and above it different shaped foraminifera. What had happened?

It became apparent to Alvarez that there had been a mass extinction from a cataclysmic event and we now have evidence to support a meteoric strike in the Yucatán Peninsula which caused a global catastrophe. Alvarez proposed that it “was not the impact itself or even the immediate aftermath. The truly catastrophic effect of the asteroid – or, to use the more generic term, bolide – was the dust.”[15] The organisms in the layer above the clay included ammonites and for whatever reason they survived over those millions of years which was lucky for us because “everything (and everyone) alive today is descended from an organism that somehow survive the impact.”[16]

Carbon dioxide had also played a role in extinctions. A volcanic eruption in 1302 provided an opportunity to study the effect of carbon dioxide on the water. As Flannery pointed out in Atmosphere of Hope, “The best-studied vents are those around Castello Aragonese in the Tyrrhenian Sea, 40 kilometers west of Naples.”[17] Kolbert wanted to see the vents that were emitting the gas first hand and dove with two marine biologists. She observed how the number of organisms declined as they got closer to the vents and this was the result of a more acidic water; CO₂ combines with water to form carbonic acid. pH of ocean water is around 8.2 and while a drop to 8.0 might not seem significant, for those organisms including humans who require a stable pH, it can be deadly. “Since the start of the industrial revolution, humans have burned enough fossil fuels – coal, oil, and natural gas – to add some 365 billion metric tons of carbon to the atmosphere…As a result of all this, the concentration of carbon dioxide in the air today – a little over four hundred parts per million – is higher than at any other point in the last eight thousand years.”[18] This increase in carbon dioxide leads to ocean acidification which is sometimes “referred to as global warming’s ‘equally evil twin’…It played a role in at least two of the Big Five extinctions (the end-Permian and the end-Triassic) and quite possibly it was a major factor in a third (the end-Cretaceous).”[19] Also as we learned from two class presentations, ocean acidification is having a devastating effect on coral reefs; coral needs calcium carbonate to build its skeleton.

Extinctions can result from the introduction of a new organism or species. As Kolbert mentioned previously, humans transport organisms from one location to another and she provided several examples of species which have been adversely affected. Bats in a cave in New York were discovered with a white powder on their noses which was later identified as a fungus which somehow travelled on some type of carrier from Europe. Species moving around the globe result in one of a couple of scenarios: one, they cannot survive at their new location and die or two they survive and either remain in the locality or spread to other areas.[20] The second scenario can lead to some very destructive consequences. Kolbert cites the brown tree snake that “found its way to Guam in the nineteen-forties, probably in military cargo.”[21] It has completely destroyed several species of birds on Guam. Another example was the Cryphonectria parasitica, a fungus that attack American chestnut trees. “In the eighteen hundreds, the American chestnut was the dominant deciduous tree in eastern forests; in places like Connecticut, it made up close to half the standing timber.”[22] Today it is non-existent. No wonder there are no more chestnuts roasting on an open fire. The fungus probably came from Japan where the chestnut trees there had developed a resistance to the fungus.

Modern humans have not only altered the environmental aspects of the world through pollution and industrial wastes and by-products but they have interacted with species which are some our closest ancestors in ways which has resulted in their extinction.  For years Neanderthals have been the subject of derision. It is only recently with the work of paleo geneticists that we are gaining a better understanding of the life of the Neanderthal and how part of their DNA exists in modern human beings as a result of some interbreeding. The demise of the Neanderthals may reflect the manner in which modern humans competed for space and resources and eventually drove the Neanderthals to extinction. “There is every reason to believe that if humans had not arrived on the scene, the Neanderthals would be there still, along with the wild horses and the woolly rhinos. With the capacity to represent the world in signs and symbols comes the capacity to change it, which, as it happens, is also the capacity to destroy it.”[23]

In conclusion, as we have seen the Great Five extinctions were not the result of human actions, but lets us hope that we will realize in time that our actions could lead to the Sixth Extinction which could be us and that we will take the necessary steps associated with self-preservation.

           

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[1] http://www.bbc.co.uk/nature/extinction_events

[2] Colin Renfrew and Paul Bahn. Archaeology: Theories, Methods and Practice. (New York: Thames & Hudson, 2016), 167.

[3] Jeanne Ballantine, Keith Roberts, and Kathleen Korgen. Our Social World. (Thousand Oaks, CA: SAGE Publications, Inc., 2016), 60.

[4] Ibid., 62.

[5] https://ourworldindata.org/world-population-growth/

[6] Elizabeth Kolbert. The Sixth Extinction. (New York: Henry Holt and Company, LLC, 2014), 1-2.

[7] Ibid., 2.

[8] Ibid., 13.

[9] Ibid., 24.

[10] Ibid., 27-28.

[11] Ibid., 46.

[12] Ibid., 58.

[13] Ibid., 72.

[14] Ibid., 73.

[15] Ibid., 86.

[16] Ibid., 90.

[17] Tim Flannery. Atmosphere of Hope. (New York: Atlantic Monthly Press, 2015), 37.

[18] Kolbert, The Sixth Extinction, 113.

[19] Ibid., 120.

[20] Ibid., 201.

[21] Ibid., 203.

[22] Ibid., 204.

[23] Ibid., 258.