THE CHICXULUB ASTEROID 2 Running Head: THE CHICXULUB ASTEROID 1 The Chicxulub

THE CHICXULUB ASTEROID 2

Running Head: THE CHICXULUB ASTEROID 1

The Chicxulub Asteroid and the End-Cretaceous Mass Extinction

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Abstract

The mass extinction of dinosaurs is an issue that has been treated with fascination by many, including scholars, scientists, and ordinary people. Multiple explanations have been brought forward to explain these five major mass extinction events. This paper focuses on the mass extinction of the End-Cretaceous period and the debate as to whether this extinction event was caused by either an asteroid’s impact or volcanic activity. Both explanations are presented, and reasons are given as to why an asteroid’s impact is the most likely cause of the mass extinction event. The Chicxulub asteroid and its impact is explained in detail, including the forces that were put in motion that brought about the extinction of dinosaurs among other flora and fauna. The paper concludes by explaining the effects that the climate change caused by the asteroid had on the planet’s life forms.

Climate change has played a critical role in shaping biodiversity; major mass extinctions are linked to thresholds in climate change. Extensive research indicates that abrupt climate change involving both cooling and warming events as direct and indirect causes of both minor and major extinctions. The End-Ordovician mass extinction, for instance, is associated with a cooling event accompanied by glaciation and a major decrease in the sea level. The Permian-Triassic mass extinction, on the other hand, was associated with a period of climate warming. There have been five major mass extinction events that have shaped the evolution of the earth to its current state. Each of these extinction events essentially brought an end to a number of species while simultaneously creating new ecological niches for the organisms that would, later on, inhabit the earth (Burgess, 2019). The understanding of these extinction events can therefore be used to inform the understanding of how responsive the biosphere is to the dramatic changes in the environment and hence possibly predict the outcomes of anthropogenic changes. Rock records of past extinction can be used to understand the interconnectedness between climate change, the oceans, and the organisms that depend on these systems.

The K/Pg extinction marking the boundary between the Cretaceous and Paleogene periods (66 million years ago) brought an end to non-avian dinosaurs among other flora and fauna. In the 80s and 90s, research conducted would find that there were high iridium concentrations at this boundary, impact ejecta, and shocked minerals. The discovery of an impact crater on the Yucatan peninsula would lead to the implication that an asteroid was responsible for this extinction event, among others like it. Asteroid impact and flood basalt emplacements periods have been associated with environmental crises since the beginning of complex life on earth (Burgess, 2019). However, extinction events would also coincide with volcanic activity, and as such, another school of thought would associate these extinctions with volcanic activity. This is based on the fact that intrusions and eruptions of huge volcanic rocks into the earth’s crust can emplace millions of cubic meters of magma. This can bring about huge environmental changes since eruptions lead to the emission of large amounts of greenhouse gases.

The asteroid theory is, however, still more favored when it comes to the K/Pg mass extinction because an asteroid’s impact can be so devastating, emitting high levels of thermal radiation from the impact plume, bringing about hurricane force winds and the likelihood to cause tsunamis and landslides (Brugger, Feulner & Petri, 2017). Global consequences are necessary for extinction to occur, and in this particular case, the killing mechanisms were short term cooling and darkness due to the dust, soot, and sulfur, long term warming due to the release of massive amounts of CO2, ocean acidification, and global firestorms as the ejecta heats up entering the earth’s atmosphere and emitting thermal radiation.

The asteroid which impacted Chicxulub (present-day Gulf of Mexico) was 10km in diameter and left a crater of about 180-200 km deep. According to this explanation, the impact-induced shock waves at the Chicxulub site produced sufficient pressure to pass through sedimentary rocks, which decomposed to form part of an expanding impact plume. Since the seawater, the evaporite, and porous carbonates formed the upper layer of the target, this led to the injection of CO2, water vapor, and sulfur-bearing gases into the atmosphere. Sulfur then formed aerosols which then absorbed radiation leading to the rapid cooling of the earth’s surface, CO2 on the other hand, led to the long-term warming of the climate (Brugger, Feulner & Petri, 2017).

The Deccan volcanism (Present-day India) as an explanation for the K/Pg mass extinction is justified by volcanism being historically the major driver of changes in the planet’s climate. Volcanism has been identified as the major cause of the most extreme biotic crisis since the formation of the earth, the End-Permian mass extinction, and quite possibly the Triassic/Jurassic mass extinction (Chiarenza et al., 2020). There were, however, significant differences between the End-Permian mass extinction and the K/Pg event: during the End-Permian extinction, some animals went extinct at different time periods. More so, the ocean acidified, becoming anoxic, which is indicative of a slower geological process. The End-Permian event was, therefore, a prolonged and multi-phased extinction process. The K/Pg event, however, occurred instantly with no clear proof of a long decline that would be required for Deccan volcanism to bring about a mass extinction event. Research on marine macrofossils in Antarctica also confirms that there was a sudden calamitous catalyst for extinction, such as an asteroid impact rather than volcanic activity in the Deccan region (Chiarenza et al., 2020). More recent studies have also found no correlation between the Deccan volcanic influence and global climate change, questioning Deccan’s volcanism as a driver of extinction. This is supported by the fact that following previous high-intensity volcanic events with Deccan as the epicenter, animals had been able to survive. More so, the magnitude of the releases in the Deccan region barely approaches the lower estimates of the Chicxulub impactor. The physical and chemical impact of Deccan volcanic activity was, therefore, not enough to bring about the annihilation of non-avian dinosaurs since the impact of the volcanism alone could not account for the extinction. Chieranz et al. (2020) argued that Deccan was far more influential following the extinction event in shaping ecological recovery rates after the planet’s temperature had been lowered considerably. It is also very likely that most of the intense volcanic activity occurred after the mass extinction event had passed (Chiarenza et al., 2020).

The asteroid’s impact was therefore devastating to the earth’s climate. The asteroid collided with the rocks to produce hundreds of gigatonnes of sulfates leading to a cooling effect and 3 to 16 years of subfreezing temperatures, and a recovery period of over 30 years. There were freezing temperatures even in the tropics, which led to the disruption of large food supply for the animal population (Artemieva, Morgan & Expedition 364 Science Party, 2017). Apart from dinosaurs, other animals were also affected by the mass extinction event: birds, mammals, and squamates were also hit by extreme extinction rates. Organisms from a broad selection of distinct ecologies were affected by the extinction event. The determinants behind the selection process of animals affected include body size, habitat, diet, physiology, and geographic range (Artemieva, Morgan & Expedition 364 Science Party, 2017). These characteristics are associated with changes in temperature. Refuge from extinction-level temperatures may have been found in the deep valleys, coastal regions, fluvio-lacustrine systems, and the tropics, which offered refuge to birds, mammals, crocodiles, lizards, snakes, and all other animals that survived this extinction period with relatively lower species loss.

References

Burgess, S. (2019). Deciphering mass extinction triggers. Science, 363(6429), 815-816.

Brugger, J., Feulner, G., & Petri, S. (2017). Baby, it’s cold outside: Climate model simulations of the effects of the asteroid impact at the end of the Cretaceous. Geophysical Research Letters, 44(1), 419-427.

Artemieva, N., Morgan, J., & Expedition 364 Science Party. (2017). Quantifying the release of climate‐active gases by large meteorite impacts with a case study of Chicxulub. Geophysical Research Letters, 44(20), 10-180.

Chiarenza, A. A., Farnsworth, A., Mannion, P. D., Lunt, D. J., Valdes, P. J., Morgan, J. V., & Allison, P. A. (2020). Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction. Proceedings of the National Academy of Sciences, 117(29), 17084 17093.