Assessing the Effects of the Asteroid on Dinosaurs

The most widely accepted cause for the extinction of non-avian dinosaurs, at the end of the Cretaceous period, is the asteroid impact. The theory suggests that the impact of a giant asteroid, over 65 million years ago, wiped out the land roaming dinosaurs that inhabited the Earth for the entirety of the Mesozoic period (Alvarez and Asaro, 1990). The impact of this giant asteroid had many catastrophic effects on life, habitats, environments, sunlight, and temperature, proving to be devastating on the life of dinosaurs (Alvarez and Asaro, 1990). However, which of the impacts of this asteroid was most devastating to non-avian dinosaur life remains a question. An examination of several effects of the asteroid, will help us determine which factors proved to be most troublesome to dinosaurs, which effects could have been adapted and overcome, and which would pull out a critical peg in the food chain, thereby forcing the ecosystem’s stability to become unbalanced and dysfunctional. So, the asteroid at the end of the cretaceous period was destructive and disastrous, but what factors made it so detrimental to dinosaurian life?

Firstly, why is the asteroid the most widely accepted theory as the cause of the dinosaur extinction? What evidence do we have that makes it convincing? The first piece of evidence that points towards an asteroid impact is the fossils of single-celled marine animals. Their fossil accumulation is fairly large, and their extinction appeared to be incredibly abrupt (Alvarez and Asaro,1990). This revelation is also evident in medium sized animals, as their extinctions also appear to be unusually abrupt (Alvarez and Asaro, 1990). This abruptness suggests a sudden catastrophic event to be the cause of the extinction, rather than a gradual decline. Coupled with this, through study of strata by Jan Smith and Isabella Premoli, we see that the extinction could have been as short as 50-1000 years (Alvarez and Asaro, 1990).  But why is the cause of this rapid change an asteroid? The answer is in iridium. Iridium is an element that is quite rare in the earth’s crust, however it is quite abundant in primitive stony meteorites. And upon studying the data from the time frame of the extinction, there appears to be drastically more iridium than in other time periods (Alvarez and Asaro, 1990). About 95 sites throughout the world have confirmed remarkably high levels of iridium in the limestone sediments from that period (Alvarez and Asaro, 1990). These elevated levels of iridium provide clear evidence for an extraterrestrial impact. The minerals apparent in this time frame are also indicative of an asteroid. Mineral spherules were found chemically altered in the KT boundary clay. These spherules started as basaltic rock (Alvarez, 1990). Now, an asteroid with this level of lethal power would most certainly leave its mark on the Earth. It is believed that this mark is the Chicxulub Crater in Mexico, a massive 180 km crater (Hildebrand, 1992). Knowing the magnitude of this mark will then help us determine what the effects were, and, ultimately, what were some of the most detrimental towards dinosaurian life.

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Before we assess the factors, however, we must first confirm that dinosaurian life was not gradually declining, or in the process of extinction, before this abrupt impact. For, if dinosaurian life was already in the downswing, then the asteroid impact may be regarded as less important, less detrimental, and no longer synonymous with the extinction of dinosaurs. While some studies seem to suggest that dinosaurian life was in a decline during the late Cretaceous period, one study in particular seems to suggest otherwise. The article, “Dinosaur Morphological Diversity and the end-Cretaceous extinction” explains how, in most clades, the disparity remained relatively consistent during the late Cretaceous (Brusatte, Butler, Preto-Marquez, Norell, 2012). It demonstrates how the carnivorous theropod, and small-medium sized, herbivorous dinosaur disparity was consistent throughout the period, showing no major changes in diversity (Brusatte et al. 2012). Also, the large sauropod dinosaurs without advanced chewing capabilities may have even seen an increase in disparity, while the ones with the advanced chewing abilities were showing a decrease (Brusatte et al. 2012). This suggests more of an evolutionary change rather than a trend towards extinction. The studies from the Hell Creek Formation that seemed to represent a decline in dinosaurian diversity before the end of the Cretaceous, may, then be perceived as a unique, local anomaly, rather than a representation of global diversity (Brusatte et al. 2012). For, it appeared that the diversity of species could differ based on geographical location, and one data set would not be an accurate representation of the period as a whole (Brusatte et al. 2012). Thus, the study confirms that the variability in dinosaurian morphology was, “both clade and region specific” (Brusatte et al. 2012), further exemplifying that the decline was not apparent throughout the globe. This information allows us to then make the assumption that dinosaurs were still, in fact, thriving at the time of the asteroid impact. Making the consequences that followed an unwarranted and unfair ending to a fascinating era in history.

First consider the direct effects of the asteroid impact. The most immediate impacts of the asteroid would be devastating to the dinosaurs who found themselves unlucky enough to be near where it landed. An asteroid that was, theoretically, 10 km long, due to the kinetic energy, would create an explosion 10,000 times that of the entire worlds supply of nuclear power (Alvarez and Asaro, 1990). The impact alone had the ability to create winds as fast as 1000 km/h near where the asteroid hit (Kring, 2007). This high wind speed would have the ability to create local fires, and wipe out vegetation and animal life in the area (Kring, 2007). These local fires had the energy to spread, likely, from 1500 km-4000 km from where the impact occurred (Kring, 2007). The mushroom cloud of this explosion would be approximately 10 kilometres high, have a temperature of up to 10 000 degrees Celsius, and would wipe out anything within sight of the fireball (Alvarez and Asaro, 1990) (Kring, 2007). It is also estimated that the dust in the air would be so dense that one would be unable to see their hand for several months after the explosion (Alvarez and Asaro, 1990). This dust would cause major respiratory problems for any dinosaur near the explosion, and would likely render them unable to breathe. However, the only problem wasn’t airborne, it was in water as well.

Another detrimental effect created by the initial impact of the asteroid was tsunamis. Tsunamis enveloped the entire coastline of the Gulf of Mexico, reaching North America in the process (Matsui et al., 2002). The tsunamis were truly massive, extending to a height of 200 m and stretching along 300 km of coastline (Matsui et al., 2002). The tsunamis would first collapse onto the coast, a distance of 150 m inland, before receding powerfully back to the water (Matsui et al., 2002). These tsunamis would be catastrophic to coastal vegetation and dinosaurian life; however, the damage would have had more of a regional effect rather than a global one. The tsunamis were also present for little more than a day, making it not a recurring, long-term issue, but a short-term effect (Kring, 2007). While most inland dinosaurs were likely spared from these tsunamis, they did not, however, find themselves in the clear.

Plant life, the vegetation that allows animals to breathe, thrives on the process of photosynthesis. Photosynthesis, in turn, relies on sunlight. The significant levels of dust in the atmosphere would have spread rapidly throughout the planet, blocking out the sun, causing darkness and an “impact winter” (Alvarez and Asaro, 1990). This blocking of sunlight was predicted to have killed anywhere from 57-80% of North America’s vegetation (Archibald, 2012). This kind of catastrophic massacre of vegetation would have been undoubtedly impactful on the herbivorous dinosaurs (Archibald, 2012). Especially, one might assume, large sauropods that required substantial levels of nutrients and energy to survive. And, according to the food chain, a loss of herbivorous dinosaurs would prove costly to the carnivorous theropods that fed on them. The dust from the impact also created atmospheric cooling, however, just how cold it made Earth is still in question (Kring, 2007). This surface cooling, however, didn’t last long, and was eventually replaced by extreme temperature increases.

These extreme temperature increases, once the dust subsided, were a result of the ozone destruction in the atmosphere. “Ozone destroying Cl and Br can be produced from the vaporized projectile, vaporized target lithologies, and biomass burning” (Kring, 2007), showing that lethal changes in nitrogen chemistry, created by the asteroid, leaked into the atmosphere. Over five times more chlorine that is required to destroy our current ozone layer was dispersed throughout the stratosphere at this time (Kring, 2007). A greenhouse gas that we have become so acquainted with in today’s society, was also working with the same diligence after the asteroid impact. Water and carbon dioxide were released after the impact of the asteroid, and once the dust settled, the impact winter shifted into global warming (Alvarez and Asaro, 1990). Carbon dioxide would have lasted longer than the dust from the impact, so its association in this sequence of natural disasters seems logically accurate (Kring, 2007). Based on evidence from carbon dioxide that was added to the atmosphere, it is projected that it would increase the global temperature anywhere from 1-7.5 degrees Celsius (Kring, 2007). Despite this evidence, it is unclear how large of an impact this global warming had on the dinosaurs, for the destruction of vegetation caused by the dust in the atmosphere appears to be the driving force behind the extinction (Archibald, 2012). But was the sunlight blocking mechanism of the dust the only damage inflicted by the aerosols?

Dust had the capability to attack in a vertical, gravity driven onslaught on the helpless dinosaurs. Evidence shows that the impact of the asteroid can create nitric acid rain in the atmosphere (Kring, 2007). This acid rain would surely be devastating to any dinosaur that found itself under this caustic weather. It was even described as, “an acid rain with a vengeance” (Alvarez and Asaro, 1990), only reiterating the devastating effect the acid rain could have produced. Now, this acid rain may have not lasted long, for it is predicted that it only fell anywhere from a couple months to a few years (Kring, 2007). Nitric acid was not alone in its onslaught. It is believed it was coupled with sulfuric acid rain (Kring, 2007). The sulfuric acid rain emerged as nitric acid’s accomplice because the Chicxulub region was abundant in anhydrite (Kring, 2007). This deadly combination certainly sounds imposing, but much like the global warming, the magnitude of its impact on the non-avian dinosaur extinction is questionable. This is because acid rain is generally most effective against aquatic organisms, but aquatic organisms survived quite well through the K/T boundary (Archibald, 2012). Their survival serves to diminish the effectiveness of the acid rain. This is not to say that the acid rain was underwhelming, though, only that it was limited in its ability to cause a major extinction.

One result of the impact that contributed to the dust was global wildfires. The severity, location, and longevity of these fires is, however, uncertain (Kring, 2007). The global abundance of soot suggests that the fires were almost everywhere. However, soot has the ability to travel through air, enabling it to settle in the ground where there wasn’t a fire (Kring, 2007). Some model calculations also seem to suggest that the temperatures on the surface of the earth may have been hot enough to spark into a fire almost randomly (Kring, 2007). Our ability to predict the vastness of the global fires relies on our understanding of the mass of the ejecta, how easily the vegetation lights, and the rate in which it can spread (Kring, 2007). Depending on these factors, the wildfires may have been limited to more of a local fire, rather than a global one (Kring, 2007). The speculation surrounding the impact of global wildfires appears to be unpredictable and baseless, including the prediction of it destroying 25% of all biomass (Archibald, 2012). Overall, it seems the lack of evidence found in the minimal amounts of charcoal, and a limited fossil record, outweigh the theories of a devastating global wildfire (Archibald, 2012). These sources display that a wildfire was almost certainly local, but unlikely to be global.

With all of these factors, now compiled, that followed the asteroid’s impact, can we come to a claim as to which was the most destructive? The dinosaurs extinction most certainly hinged on several factors, however, it appears that one in particular proved to be the most effective. The factor that most sufficiently damaged the survival of the thriving dinosaurians was, through the evidence above, the dust and aerosols that served to block out the sunlight. The loss of vegetation, sunlight, and heat directly drilled a fatal hole in the food chain. Losing vegetation, then herbivores, then carnivores, appeared to not only cause the ecosystem to dwindle, but caused it to be rid from non-avian dinosaurian life. The impact itself was an imposing warning, the dust was the main force of destruction, and the acid rain, global warming, wildfires, and loss of ozone were supplementary, inconclusive forces.

Although this unimaginable series of events is approached with mostly scientific fascination and curiosity, and perhaps melancholy for the loss of dinosaurs, it could also be viewed as a notable and necessary precursor to the introduction of other lifeforms on Earth. For, without this dinosaur extinction, the tiny mammals that occupied the earth would be restricted in their evolution, ruled over, and unable to transition into vast abundance (Alvarez and Asaro, 1990). Highly intelligent humans stemmed from the survival of these mammals, and, in turn, stemmed from the impact of that fatal asteroid 65 million years ago.

List of Works Cited

Alvarez, W., & Asaro, F. (1990). An extraterrestrial impact. Scientific American, 263(4), 78-84.

Brusatte, S. L., Butler, R. J., Prieto-Márquez, A., & Norell, M. A. (2012). Dinosaur morphological diversity and the end-Cretaceous extinction. Nature Communications, 3, 804.

Silver, L. T., & Schultz, P. H. (Eds.). (1983). Geological implications of impacts of large asteroids and comets on the Earth (Vol. 190). Geological Society of America.

Archibald, J. D. (2012). Dinosaur extinction: Past and present perceptions. The Complete Dinosaur, 1027-1038.

Kring, D. A. (2007). The Chicxulub impact event and its environmental consequences at the Cretaceous-Tertiary boundary. Palaeogeography, Palaeoclimatology, Palaeoecology, 255(1), 4-21.

Matsui, T., Imamura, F., Tajika, E., Nakano, Y., & Fujisawa, Y. (2002). Generation and propagation of a tsunami from the Cretaceous-Tertiary impact event. SPECIAL PAPERS-GEOLOGICAL SOCIETY OF AMERICA, 69-78.