Extinctions Due to Confluence

I have said for a long time that the whole idea of pinning mass extinctions on a single event was not constructive. Rather, it made much more sense to think of the global ecosystem as fairly resilient, such that true mass extinctions would only occur when multiple events coincided. Apparently Arens and West agree with me. They published a paper in the December issue of Paleobiology (http://paleobiol.geoscienceworld.org/cgi/content/abstract/34/4/456) indicating that mass extinctions occurred when a "press" event, such as extensive volcanism stressing the ecosystem over time, coincides with a "pulse" event, such as a bolide impact, that causes acute and sudden catastrophe. The 1-2 punch is what causes the mass extinction. Finally, someone has published a good statistical and rigorous study demonstrating what I have been saying for years but never actually did a rigorous analysis to prove. Good for them.