End Cretaceous Mass Extinction

The extinction of the dinosaurs, absolutely a thrilling topic. In Steven Gould’s persuasive article he goes into great detail to describe the nature of science and it’s profound nature to help us in the pursuit of knowledge when used correctly. He then begins to describe three scenarios in which could’ve led to the extinction of the dinosaurs in which two while seemingly plausible at first glance are in actuality simply speculation. Thus, just like a good hypothesis using evidence to support his critiques and support of the hypotheses. Which is why I agree with Gould’s statement on how out of the three hypotheses, the extinction of the dinosaurs

The Cretaceous period is a period of time within the Mesozoic Era lasting from 146 million years ago to 65.5 million years ago. It is one of three periods in the Mesozoic Era along with the Triassic and Jurassic periods. The Cretaceous period is well known for the amount of dinosaurs it had, and the event that put an end to the dinosaurs reign, the K-T mass extinction. During the K-T mass extinction, a huge asteroid hit earth and caused tons of dust to infiltrate the air. Only a small portion of dinosaurs died on impact Instead, the dust blocked out sunlight which caused plants to die. Without plants, many dinosaurs did not have a food source, so the died out. Carnivore dinosaurs, such as the Tyrannosaurus Rex, survived a little longer

Dinosaurs ruled the earth for over 65 million years and thankfully for the human race, they became extinct. Ultimately, only a major catastrophe could completely wipe out an entire species, let alone an entity of dinosaurs and the debacle on the causes of dinosaur extinction have flooded the minds of paleontologists for centuries. Geologist and zoologist Stephen Jay Gould published “Sex, Drugs, Disasters, and the Extinction of Dinosaurs,” to compare scientific and speculative causes of dinosaur decimation. Personally, I found this passage very informational and enjoyed reading it. Gould provides three theories that capture the reader’s curiosity, allowing room for pondering in one’s mind.

The Cretaceous – Tertiary mass extinction, commonly referred to as the KT extinction, occurred 65 million years ago. As the most recant extinction event it is more easily studied as more evidence has been preserved than for the earlier extinctions. This extinction is the most commonly known, as it is the extinction of the dinosaurs, but the smallest scale mass extinction with only 76% of species dying out.

The End Cretaceous impact hypothesis states that an asteroid impact on the earth caused the extinction. The evidence that supports this hypothesis include the crater found in the Yucatan Peninsula, the rare metal Iridium, and fractured “shocked quartz” crystals that have been shown to cause high-energy explosions. The End Cretaceous flood volcanism hypothesis states that a giant volcano eruption, or a series of volcano eruptions caused the extinction The evidence that supports this hypothesis includes immense lava flow, and volcano explosions, which happen to exposed iridium.

These techniques led to the discovery of the boundary between the two eras. A single thin layer of clay found within predominantly limestone rocks established this. By comparing the marine life found in, above, and below the clay, the marine life, like the dinosaurs, had been terribly affected by the extinction event. The percentage of life in the upper layers was dramatically lower than that in the lower. This was far more compelling than what was suggested by dinosaur’s fossils.

The Cretaceous-Tertiary extinction, also known as the K-T extinction, was a global extinction event that struck the Yucatan Peninsula at the end of the end of the Mesozoic Era, 65 million years ago. Walter Alvarez first discovered a meteorite big enough to be called a small asteroid that hit the Earth, creating the Chicxulub crater. Once the asteroid struck the North American continent, there were igneous rocks underneath the crater that contained high levels of a rare siderophile element, iridium. This catrostopic event had a massive effect on the environment, as several mammals, birds, and plants became extinct. It also caused an impact winter that made it impossible for plants and plankton to photosynthesis, as 75% of inland animals and 90% of marine species were affected. Not only did it cause an impact winter, but the asteroid also caused volcanic eruptions, climate change and sea level rise. Geologists have also found rich dinosaur, plant and marine fossils to illustrate the K-T extinction. This event not only caused species to become extinct, but it also had an adaptive radiation, as other species were able to diversify.

Amid these conclusions, Faith and Surovell derived their question from the fact that one cannot develop explanations for this phenomenon without knowing whether the extinction was a long-term process or a single event. They hypothesized that the extinction during the North American late Pleistocene was a single event that occurred between 12,000 and 10,000 radiocarbon years B.P. (Faith and Surovell, 2009).

There was much speculation regarding the K/T boundary being caused by a meteorite. The impact of this event was believed to have led to extended volcanic activity periods that in turn further polluted the atmosphere. The impact of the K-T boundary happened to be attributed to the extinction of dinosaurs that might have been as a result of new diseases. The impact affected all living things including primates. The impact is believed to have drastically slowed primate evolution (Clyde, 2010).

Many people often assume the asteroid completely wiped off the land and marine species with just the impact of the asteroid, but was rather the tipping point of what came next. In fact Choi stated that “ "We have shown that these events are synchronous to within a gnat's eyebrow, and therefore, the impact clearly played a major role in extinctions, but it probably wasn't just the impact.” ( Choi). The ultimate reasons for the dinosaurs and other species extinction was the blockage of sunlight which initially darkened and chilled to earth to extreme temperatures ( Jones). At this point many animals and even plants started to die off because of the chilling conditions, but that wasn't the only reason for the extinction of these species. Soon after the dust had settled and the earth was able to receive light, the planet initiated a greenhouse affect. Which not only put the remaining species at high temperatures, but their food also became inhabitable (Choi). The evidence of an asteroid theory is supported by the impact crater, rare metal, melted rock, fractured crystals, and the fossil record (Jones). The impact crater is actually one the main key examples of why the asteroid may have been responsible for the cretaceous mass extinction. It showed the asteroid landing on the Yucatan peninsula, and traveling at 30 kilometers per second (Jones). Not

In Stephen Jay Gould’s “Sex, Drugs, Disasters, and the Extinction of Dinosaurs”, Gould investigates three possible theories hypothesizing the reason behind the extinction of dinosaurs. The first theory suggests that dinosaurs became extinct due to a rise in temperature, which caused sperm to die, leading to the sterilization of male dinosaurs. The second hypothesis offer that many dinosaurs consumed bitter plants that contained psychoactive agents which their lives could not detoxify out of their systems. The last speculation about the dinosaur’s extinction is that a large cloud of dust formed in the atmosphere after an asteroid hit Earth’s surface. This dust cloud blocked out the sunlight, causing temperatures to drop and made photosynthesis impossible. Gould uses these three theories to lead to his central claim that science isn’t just about making fascinating claims, but should have a well developed hypothesis.

“A minority disputes this theory, arguing that other events-such as volcanic eruptions, sea-level changes or a series of impacts-were to blame for the spectacular loss of species that occurred at the transition between the Cretaceous and Tertiary periods…”

Ever since the history of Earth has been studied using fossil records, extinctions have always been the object of fascination and interest, particularly the mass extinctions that occurred throughout Earth's history. A mass extinction can be caused by disruptive global environmental changes, where large numbers of species have become extinct (Urry et al. 2008). There have been five major extinctions documented based on fossil records over the past 500 million years, but the Cretaceous (KT boundary extinction – a name that meant it began the Tertiary era) extinction caught a lot of

Sixty-Five Million years ago, a giant space rock believed to be some six miles across hit Earth near the town of Chicxulub, Mexico, blasting a crater more than 110 miles wide. The impact is believed to have released as much energy as 100 trillion tons of TNT, more than 1 billion times the power of the atom bombs dropped on Hiroshima and Nagasaki during World War II. The giant mosasaurs and plesiosaurs in the seas and the pterosaurs in the skies. Plankton, the base of the ocean food chain, took a hard hit. Many families of brachiopods and sea sponges disappeared. The remaining hard-shelled ammonites vanished. Shark diversity shriveled. Most vegetation withered. In all, more than half of the world's species were obliterated.

Gerta Keller, professor of geosciences at Princeton University, has recently conducted research on the Chicxulub asteroid in which she analyzed new core samples taken from the asteroid site (Botzer 2004). These samples indicate that the impact that occurred at Chicxulub actually predated the mass extinction of the dinosaurs, which occurred at the Cretaceous-Tertiary boundary about sixty-five million years ago. Keller claims that the Chicxulub impact occurred approximately 300,000 years before the extinction (Keller 2004). Although previous researchers estimated that the Chicxulub asteroid was the cause of the extinctions, there had always been doubts about the exact age and size of the crater, and about the origin of the “mega tsunami deposits” that were located within the crater (Keller 2004). The focus of Keller’s recent research was on finding some answers to these questions. To do so she analyzed Cretaceous limestone, dolomite, and anhydrite deposits as the site of the Chicxulub crater (Keller 2004).