Cause and Effect Essay

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Oct 30, 2023

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Step 2: Cause and Effect Essay Draft 1 Two Different Theories of Cretaceous Tertiary (K-T) Mass Extinction Introduction

The geological history of the earth is full of dramatic twists and turns. The earth's climate has undergone dramatic changes, from the ice age to global warming. The evolution and disappearance of species have experienced their unique period. Five mass extinctions have been recorded in geological history, one at the end of the Cretaceous period, about 65 years ago, which is very important because it almost disappeared 70% of the life forms that lived on the earth at that time. There are two different theories about the cause of the Cretaceous tertiary (K-T) mass extinction. One is that in 1980, Alvarez and his colleagues attributed the late Cretaceous disaster to an asteroid impact. This hypothesis was questioned in the following years, and another hypothesis appeared, which was considered that volcanic activity was another cause of extinction. Volcanic Causes At present, one of the main hypotheses to explain the mass extinction of the Cretaceous Tertiary boundary (KTB), It's widespread volcanism. Because of the long-term climate warming caused by the volcanic eruption, it eventually led to the mass extinction. Volcanism of the Deccan Traps Large Igneous Province (LIPs), defined as the largest volcanic eruptions in Earth's history >100,000 km

(Ernst and Youbi, 2017), However, whether LIPs are the main cause of major biotic crises is still in dispute because extinctions in the fossil record are rarely observed directly within volcanic deposits. However ， an exception is the Deccan Traps LIP where the end- Cretaceous mass extinction is bracketed between trans-India lava flows (>1000 km long) (Keller et al., 2008, Keller et al., 2011, Keller et al., 2012). Firstly, linking Deccan Traps LIP volcanism to climate warming and the end-Cretaceous mass extinction requires a reliable proxy for volcanic emissions, as well as sedimentary sequences with complete bio- and chemo-stratigraphic records across the KPB (Keller et al.,2020). One such potential proxy is stratigraphic mercury (Hg). Volcanic eruptions are the main source of natural Hg to the atmosphere (Pyle and Mather, 2003; Pirrone et al., 2010). In Keller’s study they test Hg is a reliable proxy for Deccan volcanic emissions in the time interval spanning from the late Maastrichtian through the KPB and end-Cretaceous mass extinction in the shallow marine sediments of Elles, Tunisia, the auxiliary Global Stereotype Section and Point (GSSP) to El Kef (Keller et al.,2020). Secondly, Keller studied the mercury concentration in sediments pulse generated is correlated with Deccan volcanic eruption and climate warming. The results show that there is a positive correlation between mercury peak and climate peak. Finally, In the results Keller states that reveal pulsed Deccan volcanic eruptions identified based on Hg

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concentrations in sediments that caused long-term climate warming and biotic turnover, it eventually led to extinction. In conclusion, according to the determination of mercury concentration in sediments, mercury is produced by volcanic eruption, which is directly related to mass extinction. At the same time, it can be determined that the change of natural environment is beyond the scope of biological adaptation due to the climate warming caused by volcanic eruption, resulting in biological death. Therefore, volcanic eruption is the main factor of Cretaceous tertiary (K-T) mass extinction. Asteroid Impacts For the past 40 years, the impact theory has been regarded as the almost undoubted cause of the end Cretaceous mass extinction. Iridium is a rare metal element that extremely low quantities in crustal rocks, but in significantly higher quantities in chondritic meteorites. Based on this factor, many scientists measured the content of iridium in the crust to determine the Cretaceous extinction was related to asteroid impact. To begin with, we can find in the paper Extraterrestrial Cause for the Cretaceous-Tertiary Extinction, Alvarez et al. (1980) analyzes “concentrations of these elements in deep-sea sediments may indicate influxes of extraterrestrial material”. The second time, the researchers examined deep-sea limestone near the C-T boundary of three different extinction sites in Italy, Denmark and New Zealand, and tested the

content of various elements in limestone and detected an unusually high concentration of iridium in the boundary clay separating the Cretaceous formations from the overlying tertiary formations .Finally, in Alvarez's (1980) study shows that Deep-sea limestones exposed in Italy, Denmark, and New Zealand show iridium increases of about 30, 160, and 20 times, respectively, above the background level at precisely the time of the Cretaceous-Tertiary extinctions, 65 million years ago. This evidence suggests that iridium is not a common element in the earth's crust, this iridium is of extraterrestrial origin, comes from asteroids, comets, meteors and other space debris. Debris from the asteroid impact fell on the earth. Ultrahigh content of iridium was found in the deep-sea sediments at the site of the mass extinction, indicating that iridium came from outside the earth. According to iridium deposits around the world, and fossil records, this element is almost the same as the time of collective death. An asteroid had crashed into the Earth, spewing iridium and pulverized rock dust around the globe and wiping out most life forms. Iridium observations can be used to explain the Cretaceous Tertiary (K-T) Mass Extinction caused by asteroid collision with the earth. There are two main theories about the K-T extinction. In my opinion, asteroid impact theory is more reliable.

There are many craters on the earth, such as Arizona crater in the United States, Lonar crater in India and Klarman crater in Australia. Initially, the results of the exploration of the crater strongly support the impact theory. A typical example is the discovery of the huge (- 200 km diameter) Chicxulub crater in Mexico's Yucatan Peninsula. This crater has been dated by Swisher and coworkers in 1992 as 64.98 ± 0.05 My. Schuraytz et al. (1996) detected micron-size iridium nuggets from Chicxulub impact melt. Several cores retrieved from Yucatan peninsula also provided tangible proof for the impact event. Subsequently, researchers found iridium anomalies in many K-T sites all over the world both on land and deep-sea sections. The existing meteorite craters all over the world and the iridium anomaly found in the clay of K-T boundary are all important factors indicating the asteroid impact on the earth. Finally, the extreme size of the space debris vaulted ash, dust, and other matter into the atmosphere, essentially blocking out the Sun for long periods of time. Plants, no longer able to undergo photosynthesis, began to die off, leaving animals with no food, so they starved to death. From the study of existing craters in different locations, we can find iridium nuggets from K-T clay and the wide range and speed of mass extinction, it can be proved that the asteroid collision theory is more reliable.

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References (in APA) Alvarez, L. W. et al., (1980) , Extraterrestrial Cause for the Cretaceous- Tertiary Extinction ， Science ， American Association for the Advancement of Science DOI: 10.1126/science.208.4448.1095 Ernst, R.E., &Youbi, N. (2017) How large Igneous Provinces affect global climate, sometimes cause mass extinctions, and represent natural markers in the geological record Palaeogeogr. Palaeoclimatol. Palaeoecol., 478 (2017), pp. 30-52, 10.1016/j.palaeo.2017.03.014 Kellera, G.et al. (2020) Mercury linked to Deccan Traps volcanism, climate change and the end-Cretaceous mass extinction ， Global and Planetary Change. Volume 194, 103312, https://doi.org/10.1016/j.gloplacha.2020.103312 Keller, G.et al. (2008) Main Deccan volcanism phase ends at K-T mass extinction: evidence from the Krishna-Godavari Basin, SE India Earth Planet. Sci. Lett., 268 (2008), pp. 293-311, 10.1016/j.epsl.2008.01.015 Keller, G.et al. (2011) Deccan volcanism linked to the Cretaceous- Tertiary boundary (KTB) mass extinction: New evidence from ONGC wells in the Krishna-Godavari Basin, India J. Geol. Soc. India, 78 (2011), pp. 399-428, 10.1007/s12594-011-0107-3

Keller, G.et al. (2013) Chicxulub impact spherules in the North Atlantic and Caribbean: age constraints and Cretaceous–Tertiary boundary hiatus Geol. Mag., 150 (2013), pp. 885-907, 10.1017/S0016756812001069 Pyle, D.M., & Mather, T.A. (2003) The importance of volcanic emissions for the global atmospheric mercury cycle. Atmospheric Environment, 37 (2003), pp. 5115-5124, 10.1016/j.atmosenv.2003.07.011 Pirrone, N. et al., Global mercury emissions to the atmosphere from anthropogenic and natural sources Atmos. Chem. Phys. Discuss., 10 (2010), pp. 4719-4752, 10.5194/acp-10-5951-2010 Sukumaran, P. V. (1998). Cretaceous — Tertiary mass extinction. Resonance , 3 (3), 8– 17. https://doi.org/10.1007/bf02837610 Schuraytz, B. C., Lindstrom, D. J., Marin, L. E., Martinez, R. R., Mittlefehldt, D. W., Sharpton, V. L., & Wentworth, S. J. (1996). Iridium Metal in Chicxulub Impact Melt: Forensic Chemistry on the K-T Smoking Gun. Science, 271(5255), 1573–1576. https://doi.org/10.1126/science.271.5255.1573