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Arens Groundbreaking Research Published

Associate Professor of Geoscience Nan Arens believes that her theory about Earth’s worst mass extinctions may help settle decades of scientific debate. While major cataclysms, such as meteor impacts or dramatic climate change, are often the focus of research related to extinction, these may be the exception rather than the rule. Mass extinctions aren’t simple events with simple explanations.

“Press/Pulse,” the theory developed by Arens and research assistant Ian West ’06, gets around the scientific controversy by rejecting the all-or-nothing approach to mass extinction, calling instead on a combination of deadly sudden catastrophes – “pulses” – with longer, steadier pressures on species – “presses.”

Arens and West presented their work on the Press/Pulse theory at the annual meeting of the Geological Society of America in Philadelphia in 2006. Now, the scientific paper they wrote, “Press/Pulse: A General Theory for Mass Extinction,” that discusses background information, theory formulation, methods results and conclusions, appears in the current issue of the journal Paleobiology (November, 2008). The duo’s work is also included as an article in the just-released issue of the Public Affairs Journal at HWS. “Humanity as Press and Pulse in the Modern Mass Extinction” briefly discusses their research methods, but focuses primarily on the implications of their theory for conservation, the current biodiversity crisis and the role of humanity.

When first announced, their research received considerable press attention, including coverage in ABC News’ “Double Whammy Causes Mass Extinction,” Discovery News’ “Mass Extinctions Caused by One-Two Punch,’s Meteorite-greenhouse gases combo linked to Mass Extinction, Cosmos’ “New Theory for Mass Extinctions,” SpaceDaily’s “New Theory for Mass Extinction” and’s “Meteorite-greenhouse gasses combo linked to Mass Extinction.”

A member of the faculty since 2001, Arens earned her B.S. and M.S. from The Pennsylvania State University and an M.A. and Ph.D. from Harvard University. She is a member of Phi Beta Kappa.

For West, the academic passions developed as an undergraduate student at HWS have continued beyond college. He is currently pursuing a master’s degree in environmental education at the University of New Hampshire and hopes to combine his interest in writing with his course of study.

The abstract of their paper as it appears in Paleobiology is below.

Press-pulse: a general theory of mass extinction?
Nan Crystal Arens • October 1, 2008


Previous discussions of mass extinction mechanisms generally focused on circumstances unique to each event. However, some have proposed that extensive volcanism combined with bolide impact may offer a general mechanism of mass extinction. To test this hypothesis we compared generic extinction percentages for 73 stages or substages of the Mesozoic and Cenozoic. We found that the highest frequency of intervals with elevated extinction occurred when continental flood basalt volcanism and bolide impact co-occurred. In contrast, neither volcanism nor impact alone yielded statistically elevated extinction frequencies. Although the magnitude of extinction was uncorrelated with the size of the associated flood basalt or impact structure, crater diameter did correlate with extinction percentage when volcanism and impact coincided.

Despite this result, case-by-case analysis showed that the volcanism-impact hypothesis alone cannot explain all intervals of elevated extinction.

Continental flood volcanism and impact sharee important ecological features with other proposed extinction mechanisms. Impacts, like marine anoxic incursions, are pulse disturbances that are sudden and catastrophic, and cause extensive mortality. Volcanism, like climate and sea level change, is a press disturbance that alters community composition by placing multi-generational stress on ecosystems. We propose that the coincidence of press and pulse events, not merely volcanism and impact, is required to produce the greatest episodes of dying in Phanerozoic history.

Although there is consensus that episodes of elevated extinction have happened in Earth’s past (Raup and Sepkoski 1982; Signor and Lipps 1982; Stanley and Yang 1994; May et al. 1995; Jablonski 1996; Hallam 1998; Racki and Wrzolek 2001; Peters and Foote 2002; Bambach et al. 2004; Taylor 2004a; Wignall 2004; Bambach 2006; Peters 2006; Foote 2007; Wang and Everson 2007), their causes remain vigorously debated and anecdotal. Five broad categories of mass extinction mechanisms have been proposed: bolide impact, volcanism, sea level change, marine anoxia /dysoxia, and climate change. Biotic interactions (e.g., Hallam 1979; Dott 1983; Sepkoski et al. 2000) have also been implicated, but these biocentric hypotheses commonly involve only a single lineage and do not generally mow a broad swath through biological diversity. However, Roopnarine(2006) has shown that potentially catastrophic secondary extinctions can occur when food webs are perturbed.

Extinction scenarios that invoke more than one mechanism have emerged as detailed studies of extinction intervals revealed previously unappreciated complexity. For example, the end-Ordovician extinction has been attributed to a combination of sea level regression, rapid climate change, and fluctuations in deep ocean circulation (Sheehan 2001). Global warming that contributed to the formation of extensive marine anoxia has been suggested for the Late Devonian (Bond et al. 2004), Permian (Huey and Ward 2005), and Triassic (McElwain et al. 1999; Bottjer 2004) extinctions. The end Cretaceous extinction – long the icon for a single impact cause (Alvarez et al. 1980) – may also be a candidate for a multi- faceted explanation. Keller and colleagues (e.g., Keller 2003, 2005; Keller et al. 2003) continue to argue for the synergy of volcanism, climate change, and impact. Others (e.g., Racki and Wrzolek 2001; Glikson 2005) proposed, anecdotally, that the combination of impact and extensive volcanism explained high extinction at various intervals. White and Saunders (2005) modeled the statistical frequency of impact, volcanism, and elevated extinction to show that these events were likely to have coincided three times during the last 300 Myr. They further noted that three of the traditional “big five” (Raup and Sepkoski 1982) Phanerozoic mass extinctions (Permian, Triassic, and Cretaceous) occurred within this temporal window. However, their analysis did not systematically evaluate the temporal coincidence of impact, volcanism, and mass extinction, nor did they consider the wider range of elevated extinction intervals that have been identified (MacLeod 2004; Bambach 2006; Wang and Everson 2007).

In this paper, we present a quantitative test of the impact-volcanism hypothesis. We propose that intervals of elevated extinction occur more frequently when extensive volcanism and impact coincide. In corollary, neither volcanism nor impact alone increases the frequency of elevated extinction.