Hobart and William Smith Colleges

17 February 2009 Press/Pulse in Discovery News

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 arent simple events with simple explanations. Associate Professor of Geoscience Nan Arens and alum Ian West 06, who was her research assistant at the time, developed a theory about Earths worst mass extinctions, Press/Pulse, that may help settle decades of scientific debate.

Press/Pulse 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.

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).

When first announced, their research received considerable press attention, including coverage in Discovery News, Mass Extinctions Caused by One-Two Punch. With the publication of the article in Paleobiology, Discovery News has updated that article.

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.

West 06 is currently pursuing a masters degree in environmental education at the University of New Hampshire and hopes to combine his interest in writing with his course of study.

The updated Discovery News article follows.

---

Discovery News
Mass Extinctions May Follow One-Two Punch
Michael Reilly Feb. 17, 2009

As agents of extinction, comet and asteroid impacts may be losing their punch.
According to a new theory about how mass dyings work, cosmic collisions generally arent enough to cause a major extinction event. To be truly devastating, they must be accompanied by another event that inflicts long-term suffering, like runaway climate change due to massive volcanic eruptions.

In other words, a comet couldnt have killed the dinosaurs by itself unless they were already endangered species.

This kind of one-two punch could explain more than the extinction of dinosaurs, Nan Arens of Hobart and William Smith Colleges said. In a recent paper in the journal Paleobiology, she and colleague Ian West argue that there are two types of events that can cause extinctions pulses (quick, deadly shocks, like comets) and presses (drawn-out stresses that push ecosystems to the brink but may not kill outright, like million-year-long volcanic eruptions).

The chances of mass dyings go way up when both happen together, argues Arens.

But are all mass extinctions created equal? Can researchers come up with a Grand Unified Theory of ancient apocalypse?

West and Arens think so. They combed the last 300 million years of geologic record, noting impact craters, massive eruptions, periods of ancient climate change, and then comparing them to extinctions. The rate at which species die off spiked dramatically, they found, when a pulse-type event occurred within a million years or so of a press.

The theory fits well for the dinosaurs. Around the time of their demise 65 million years ago, a comet slammed into the Yucatan Peninsula and a huge volcano, the Deccan Traps, was erupting in what is today India.

But other extinctions are problematic. The greatest dying in geologic history, the Permian-Triassic extinction, killed 90 percent of all life on Earth, but there is no record of an impact. Instead, all signs point to a 200,000-year-long volcanic eruption in Siberia as the murder weapon.

Arens theory argues that impacts are weaker in effect than is generally thought. But a growing consensus of researchers believes that doesnt go far enough. They believe eruptions, not cosmic impacts, are the real killers.

Im not so sure craters really have anything to do with it, Gregory Retallack of the University of Oregon said, adding: I dont like the press term very much. If you look closely at the isotope record, you can see that flood basalts [large-scale eruptions] are a series of pulses, paving the golden path toward annihilation.

Im not saying its impossible to have an extinction with just a press or a pulse event, Arens admitted. The study states only that its more likely when the two combine.

Humanity is creating exactly that scenario today, she said. Over the last 6,000 years, subsistence farming began changing the climate and clearing wilderness slowly enough to constitute press-type stresses on the environment. But people began burning fossil fuels in earnest during the Industrial Revolution, and carbon concentrations have skyrocketed while growing population numbers have led to widespread habitat loss around the globe.

Arens argued this constitutes a pulse event, and the sixth great mass extinction may already be underway.