Finding single reasons for major events is curiously satisfying. Thus the notion that an asteroid strike did away with the dinosaurs — pinning their mysterious demise on one hammerblow from outer space makes sense out of what had seemed inexplicable. But a new theory challenges the single-cause notion of mass extinctions, and questions whether sudden catastrophes in combination aren’t needed to deliver the punch.
The work, to be presented today at the annual meeting of the Geological Society of America in Philadelphia, divides the last 488 million years of geologic history into distinct groups and characterizes each. So-called Pulses are times of sudden, catastrophic events like asteroid impacts, whereas Presses are periods of multigenerational stress on ecosystems, such as massive volcanic eruptions.
Nan Crystal Arens and Ian West (Hobart & William Smith Colleges) chart the history of marine organisms and extinctions through the fossil record to conclude that extinctions in times of Pulse or Press are statistically similar. It is only when Press and Pulse events coincide that a spike in extinctions occurs. “Statistically speaking, extinction rates are not significantly higher at times of impact or volcanism vs. no geologic events,” West said.
Centauri Dreams often cites evidence for extinction events seemingly triggered by incoming debris from the Solar System, such as the Chicxulub crater in the Yucatan associated with the dinosaurs’ demise, or the much larger crater recently found in Antarctica that may have been involved in the Permian-Triassic extinction. Arens and West would doubtless tell me to slow down because extinction events are complicated. Here’s Arens:
“In the modern world, species are commonly endangered by some stress before the final death blow falls. It seems likely that biological systems in the past worked in similar ways. By demonstrating that the coincidence of long-term stress and catastrophic disturbance is needed to produce big extinctions, we hope to break down some of the polarization characteristic of many discussions of extinction. We hope to send people back to the data with a more inclusive hypothesis to test.”
So much the better, and perhaps we can draw some useful inferences for today’s world out of all this. Arens’ comment about modern species relates to her idea that human beings can act as both Press and Pulse, manipulating the environment since the advent of agriculture (the Press) and triggering swift change by industrialization (the Pulse). Are we not entering an era of swifter extinctions by destroying habitats at a record pace? It’s a grim thought, but if Pulse and Press are now working simultaneously, we had better find out whether this link to ancient extinctions has genuine validity for a technological society.