I n t r o d u c t i o n to e a rt h s c i e n c e | S p r i n g 2 012
THE KT Extinction What killed the dinosaurs?
Asteroid Volcanoes
or Other?
A Look at 65 Million Years Ago
The mystery as old as time, kind of
Contributors Authors
Trish Thiesfeld Nicole Campion Kasey Bowman Danielle Roe Aaron Trigg Editors
Kasey Bowman Danielle Roe Design
Aaron Trigg
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THE 4
GREAT DEBATE
Kt EXtinCtion
The extinction of the dinosaurs has been a hot topic for generations. There have been many theories trying to explain the event that marked the mass extinction that not only wiped out the dinosaurs, but nearly 70% of all plants and animals living about 65.5 million years ago. Two of these theories fit
extraordinarily well with the evidence collected in the recent years and some others, not so well. The first theory that has gained much of the attention is an asteroid event and the second, massive volcanic eruptions. in order to find the answers, we need to take a look at a little bit of Earth’s history as well as the evidence scientists have uncovered about these two theories. We can then put our story together on this catastrophic extinction that ended the dinosaurs and many other terrestrial and marine creatures alike.
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The abrupt end of the 160 million year reign of the dinosaurs is called the cretaceous-Tertiary event, otherwise known as the K-T event. This event marked the end of the cretaceous geologic time period and moved into the Tertiary period which was what we know of to be the rise of the mammals. Although this was an unlucky time for the dinosaurs and many other creatures on Earth, it was not the first time a mass extinction took place on our planet. To fully understand what may have happened during the K-T event, knowing a little about prior events could prove insightful. As far as we know today, the Earth experienced at least five extinctions; the Permo-Triassic (P-T event) being the worst, annihilating over 95% of the all species. The P-T event is theorized to be caused by the largest known volcanic eruption in history, the effects of which lasted over a million years. Another extinction that had a notable cause was the Frasnian-Famennian event (F-F event) which was theorized to be caused by a cluster of fairly large asteroids at which time approximately 50% of all genera went extinct. Volcanoes and asteroids were a common problem during the infancy of the Earth, and these problems as we know had detrimental effects on all life.
KNOWING HOW PAST EXTINCTIONS TOOK PLACE GIVES SCIENTISTS A GOOD STARTING POINT WHEN DECIPHERING THE K-T EVENT. The first notable theory was that of geologist Dewey McLean when he discovered huge amounts of basalt had flooded out and created lava beds between india and Africa. These lava beds, known as the Deccan Traps, cover about 200,000 square miles. However, they may have covered as much as four times that amount before erosion removed much of it. The Deccan Traps have been dated within a range of 300,000 years of the K-T event. Researchers found that the Deccan volcanoes happened in three phases. The first was roughly 2.5 million years prior to the K-T event, the second, which was the largest phase, coincided with the K-T mass extinction and produced the largest lava flows in Earths’ history. This second phase expelled a vast amount of carbon dioxide and sulfur dioxide and resulted in heavy acid rain, acidic oceans, global temperatures that swung between scorching and frigid, and aerosols and ash that would have 6
Kt EXtinCtion
been carried into the stratosphere, causing long term effects. The third phase was the less severe around 300,000 years after the extinction, yet the recovery from these volcanoes was found to be inhibited by the third phase for almost 500,000 years and prolonged the severe conditions. it is easy to imagine how this type of long term event could have been responsible for the end of the dinosaurs. After all, we know that the other massive long term volcanic explosion that happened 253 million years ago resulted in the P-T extinction. However, in the late twentieth century, Luis and Walter Alvarez discovered a distinct layer of the element iridium, called the ‘iridium datum plane.’ iridium is a stable, silver-grey metal that is extremely rare on the Earth’s surface because it is bound up with iron in the core. in the rest of the solar system, it is a thousand times more common, specifically present on meteorites. They found that these layers of iridium paralleled the time of the K-T event. Another link between the asteroid impact and the K-T event is ‘shocked’ quartz in geological records. Small pieces of quartz will break away in a distinctive pattern under high levels of heat and pressure, often from high-energy impacts or explosions. These minerals are only found at nuclear explosion sites and meteorite impact sites. The traces of iridium, the “shocked quartz,” and pieces of once-molten rock, all surrounded a 150-kilometer wide crater just off the Yucatan peninsula called the chicxulub
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crater. The impact melted much of the local crust and blasted molten material outward from as deep as 14 kilometers under the surface. Small spherules of molten glass were blasted into the air at a shallow angle, and fell out over a giant area that extended northeast as far as Haiti, several hundred kilometers away, and as far northwest as colorado. The resulting impact energy was around 100 million megatons; the equivalent of 2 million hydrogen bombs exploding simultaneously. Radiation was 1000 times more than enough to ignite dry forests and caused heat equivalent to an oven on broil. in 1990, scientists made it known that the chicxulub crater was the remnant of the historic dinosaur killing event and that theory has since become dogma. Yet, many still opposed this idea and researchers on both sides of the debate went to great lengths to put their theories to the test. When taking samples of the oldest spherule of molten silica created by the asteroid, they found that the spherules lay beneath the K-T Boundary. The estimated age of this evidence predated the extinction by almost 300,000 years. What this is indicating is that the chicxulub asteroid did in fact hit the Earth, yet was possibly not the only answer for the dinosaurs’ disappearance. At one site at El Penon, researchers found 52 species present in sediments below the impact spherule layer and counted all 52 still present in layers above the spherules. However, many scientists are not ready to give up the fight for
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Kt EXtinCtion
their impact theory. Gerta Keller, professor of Geosciences, Princeton University in new Jersey, suggests that a second asteroid and perhaps even a third may have hit the Earth at the time of the K-T event. The problem with finding evidence of asteroid impacts is our regenerating planet. Any craters and evidence left behind in the oceans have long since been sub ducted beneath the Earth. Scientists will continue to hunt for evidence of what exactly happened, but there are many things we know for sure. There is strong evidence of a series of volcanoes during the time of the K-T Event. We also know of an asteroid impact 300,000 years prior to the extinction and possibly others. Many researchers believe that the asteroids during that time were the cause of the volcanic eruptions. With all these destructive events happening in the same time period, the Earth was stressed beyond belief and many animals suffered extinction because of it, vanishing from the world forever.
BOGUS THEORIES
one of these bogus theories is that dinosaurs spent too much time in the sun, got cataracts, couldn’t see very well, and thus fell off of cliffs and died. another one of these theories has to do with caterpillars. it says that they were much larger than they are today, exhausted all plant life, and therefore the herbivores ran out of food, died off, and then the carnivores followed.
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Reflection What are the two likely causes of the KT Extinction? Asteroid or Volcanic What is the name of the metal that is rare on Earth, but common on asteroids and meteorites? Iridium Where are the only two sites on Earth where shocked quartz can found? Nuclear explosion sites and asteroid/ meteorite impact sites What is the proper name for the lava beds that were caused by the volcanic eruptions 65 million years ago? Deccan Traps What was the likely rate and length of eruptions for the volcanoes? At least 30 times the rate of Hawaiian eruptions today, for about one million years. Who discovered the rare layer of Iridium? Luis and Walter Alvarez Which extinction was the worst in the history of the Earth killing over 95% of the entire species? Permo-Triassic Event How much energy was released when the supposed KT asteroid hit earth? 100 million megatons
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KT EXTINCTION
Bibliography “What Killed the Dinosaurs?” PBS. PBS. Web. 21 May 2012. <http://www. pbs.org/wgbh/evolution/extinction/dinosaurs/asteroid.html>. Imperial College London. “Asteroid Killed Off the Dinosaurs, Says International Scientific Panel.” ScienceDaily. ScienceDaily, 04 Mar. 2010. Web. 21 May 2012. <http://www.sciencedaily.com/ releases/2010/03/100304142242.htm>. -Ainsworth, Diane. “Evidence Points to Impact as Dinosaur Killer.” Evidence Points to Impact as Dinosaur Killer. JET PROPULSION LABORATORY, 12 Mar. 1998. Web. 21 May 2012. <http://www.jpl.nasa. gov/releases/98/yucatan.html>. “Dinosaur Extinction.” Animal Planet. Publications International, Ltd. Web. 21 May 2012. <http://animals.howstuffworks.com/dinosaurs/ dinosaur-extinction5.htm>. Shultz, Steven. “Dinosaur Dust-up: Princeton Paleontologist Produces Evidence for New Theory on Extinction.” Princeton - Weekly Bulletin. 22 Sept. 2003. Web. 20 May 2012. <http://www.princeton.edu/pr/ pwb/03/0922/>. Keller, Gerta. “Who Lies Sleeping?” Deccan Trap Eruptions Killed Off Dinosaurs, Not the Chicxulub Asteroid. 23 Nov. 2011. Web. 27 May 2012. <http://askwhy.co.uk/dinosauroids/?p=11366>. Wong, Kate. “Rise of Humans 2 Million Years Ago Doomed Large Carnivores.” Scientificamerican.com. 25 Apr. 2012. Web. 27 May 2012. <http://blogs.scientificamerican.com/observations/2012/04/25/rise-ofhumans-two-million-years-ago-doomed-large-carnivores/>.
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