National Geographic has a story about Earth's mass extinctions. The current biodiversity crisis is usually referred to as the "sixth mass extinction". There is even a book by that name. Of the five previous extinctions, the worst was the one at the end of the Permian. In a paper in the journal Historical Biology, Michael Rampino and Shu-Zhong Shen argue that the end-Guadapulian extinction, which occurred 259 million years ago in the middle Permian, should be considered a major extinction event.
In 1982, quantitative paleontologists Jack Sepkoski and David Raup at the University of Chicago took stock of the Earth’s worst mass extinctions, naming them the Big Five. That set includes the end-Permian, the greatest extinction event of all time, which occurred around 252 million years ago and eliminated 95 percent of marine species.
At the time, the carnage of the end-Permian overshadowed another extinction event just eight million years earlier at the end of the Guadalupian epoch. Over the last three decades, though, geologists have been digging deeper into the end-Guadalupian, and it’s more widely recognized as a distinct crisis. Now, some scientists are arguing that this ancient die-off was big enough to rank among the pantheon of past apocalypses, and they propose renaming the group of major extinction events the Big Six.
In the history of life, there have been many flameouts and setbacks. But by singling out and studying the biggest ones, geologists can begin to unearth patterns and search for common causes. Increasing evidence suggests that many global extinction events were associated with oxygen-depletion in the oceans, a symptom of greenhouse warming, and that has worrying implications for the present-day effects of climate change. The end-Guadalupian fits this trend.
“I think there’s a problem with hanging on to the number five,” says Richard Bambach, a marine paleoecologist and professor emeritus of paleontology at Virginia Tech who was a reviewer on the landmark Sepkoski-Raup paper. The end-Permian came much closer to wiping out all life when you look at the percentages. But, he says, the end-Guadalupian was astonishingly bad for biodiversity.
“If you actually look at the raw numbers,” he says, “the loss of taxa in the Guadalupian is actually greater than it was in the Permian.”
