Impacts and Mass Extinctions Revisited

Abstract

BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses.Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne's Terms of Use, available at www.bioone.org/page/terms_of_use.Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder.The Alvarez impact theory of mass extinction; limits to its applicability and the "great expectations syndrome" GRZEGORZ RACKI Racki, G. 2012. The Alvarez impact theory of mass extinction; limits to its applicability and the "great expectations syn− drome". Acta Palaeontologica Polonica 57 (4): 681-702.For the past three decades, the Alvarez impact theory of mass extinction, causally related to catastrophic meteorite im− pacts, has been recurrently applied to multiple extinction boundaries. However, these multidisciplinary research efforts across the globe have been largely unsuccessful to date, with one outstanding exception: the Cretaceous-Paleogene boundary. The unicausal impact scenario as a leading explanation, when applied to the complex fossil record, has resulted in force−fitting of data and interpretations ("great expectations syndrome". The misunderstandings can be grouped at three successive levels of the testing process, and involve the unreflective application of the impact paradigm: (i) factual misidentification, i.e., an erroneous or indefinite recognition of the extraterrestrial record in sedimentological, physical and geochemical contexts, (ii) correlative misinterpretation of the adequately documented impact signals due to their in− correct dating, and (iii) causal overestimation when the proved impact characteristics are doubtful as a sufficient trigger of a contemporaneous global cosmic catastrophe. Examples of uncritical belief in the simple cause−effect scenario for the Frasnian-Famennian, Permian-Triassic, and Triassic-Jurassic (and the Eifelian-Givetian and Paleocene-Eocene as well) global events include mostly item−1 pitfalls (factual misidentification), with Ir enrichments and shocked minerals frequently misidentified. Therefore, these mass extinctions are still at the first test level, and only the F-F extinction is po− tentially seen in the context of item−2, the interpretative step, because of the possible causative link with the Siljan Ring crater (53 km in diameter). The erratically recognized cratering signature is often marked by large timing and size uncer− tainties, and item−3, the advanced causal inference, is in fact limited to clustered impacts that clearly predate major mass extinctions. The multi−impact lag−time pattern is particularly clear in the Late Triassic, when the largest (100 km diame−...

Do Impacts Really Cause Most Mass Extinctions?

“…Instead of common causes, many scientists now see each mass extinction as a complex interaction of many different causes (Bambach et al, 2004;White and Saunders, 2005;Keller, 2005;Morrow, 2006). The most striking features of the great Permian extinction are the carbon isotopic events, which lead scientists toward hypotheses involving oceanic circulation, anoxia, hypercapnia (excess carbon dioxide poisoning), and rapid global warming (Knoll et al, 1996;Huey and Ward, 2005;Ward, 2006a, b).…”

“…But research on these topics has not stood still, even if it no longer dominates the spotlight as it did in 1980s. A lot of work has been completed on the detailed record of the major mass extinction horizons, and the past decade of research results have not gone favorably for the impact advocates (Prothero, 1999(Prothero, , 2004aKeller, 2005;Lucas, 2005;White and Saunders, 2005;Morrow, 2006;Ward, 2007).…”