Volcanism as a prime cause of mass extinctions: Retrospectives and perspectives
Published:December 31, 2019
Grzegorz Racki, 2019. "Volcanism as a prime cause of mass extinctions: Retrospectives and perspectives", Mass Extinctions, Volcanism, and Impacts: New Developments, Thierry Adatte, David P.G. Bond, Gerta Keller
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In recent models of earth-system crises, the correlation between the major Phanerozoic mass extinctions and large igneous provinces has been well established. Specifically, pulsed massive exhalations of large amounts of volcanogenic CO2 transformed Earth’s atmosphere, leading to an excessive greenhouse effect and global warming, combined with slowed oceanic circulation, oxygen deficiency, and seawater acidification. In a historical context, however, the path leading to this neocatastrophic doctrine, traced by way of ever-more-convincing proofs (in recent years, via mercury anomalies), was convoluted for many objective and notional-personal reasons. From the late eighteenth century to the revolutionary 1980s, the reception of this conceptual route in the English-language mainstream science was determined principally by the rise and fall of the orthodox nonprogressive (steady-state) paradigm of the Lyellian uniformitarian. The main cognitive steps, pioneered frequently in continental Europe, included such principal conclusions as: (1) volcanic eruptions are a natural process, consisting of heat being vented from a central incandescent core, itself a relic of an initial nebular state; (2) cataclysmic phenomena were far more intense in the geologic past, both in orogenic and nonorogenic time intervals, with a dominant nonactualistic style of fissure-type effusive activity in intraplate settings, recorded in vast trap-type basalt successions (= large igneous provinces); (3) volcanogenic gaseous emanations, dominated by carbon dioxide and water vapor, had a strong impact on the global climate in the geological past toward the global warmth mode; and (4) this “volcanic greenhouse” was deleteriously augmented by several forms of immanent stress feedback (resulting in anoxia, acidification, hypercapnia, acid rains, ultraviolet radiation, etc.). Overall, diverse global ecosystem interactions, combined with the updated large igneous province scenario, can elucidate all major destructive factors in the biosphere, such as regressive versus transgressive sea-level changes and cooling versus warming climatic responses. Notwithstanding the particularity of each major biodiversity crisis in the Phanerozoic, however, a greenhouse/icehouse volcanism-driven catastrophe is a well-confirmed key toward better understanding these biotic turnovers over a variety of time scales and feedbacks. The holistic volcanic “press-pulse” model involves the joint action of two different types of stress factors: long-lived (“press”) large igneous provinces and a variety of critically sudden (“pulse”) disturbances. Therefore, the killing effectiveness of volcanic cataclysm should be viewed not only by the large igneous province size but also by their host geology, magma plumbing system, and eruption dynamics, determining the magnitude and composition of disastrous thermogenic outgassing. In search of possible pulse signals, emphasis has recently been placed on large igneous province–related, volatile-rich, mafic-ultramafic intrusions (owing to the great fluid-bearing capacity of their magmas) and sill-type intrusions (resulting in the most-effective devolatilization of sedimentary rocks). A simultaneous burst of arc magmatism and coeval impact of arc-continent collisions (especially in tropical domain) on global weatherability are additional cumulative cataclysmic stimuli awaiting more rigorous numerical simulations.