Pop quiz: when was the most catastrophic mass extinction in the history of life on Earth? At the collapse of the Age of Dinosaurs, 65 million years ago? Bzzt. It was nearly 200 million years earlier, when the end-Permian mass extinction killed off 95 percent of all the planet's species. But it may not have had a sudden, extraterrestrial cause.
A team at Queen's University in Canada is now pointing to fossil evidence challenging the conventional wisdom that the die-out lead to the rise of mollusks, such as snails, oysters, and the pictured nudibranch. Mollusks apparently took off eight million years before the mass extinction, which suggests that prolonged climate changes (and not, say, a comet hitting Earth) were to blame:
[T]hese findings support theories suggesting the end-Permian was triggered by ocean changes long in the making, "the climax of a prolonged environmental crisis," [researcher Matthew] Clapham said.
The whole Permian period, stretching from about 300 million to 250 million years ago, saw gradual warming. This would have slowed down circulation in the ocean, eventually leading to very low levels of oxygen in the water. Massive volcanism near the end of the Permian might have wreaked even further havoc on the environment.
"Mollusks are better adapted to such stressful and changing environments, and so could have thrived," Clapham toldLiveScience. "The abundance of mollusks we see are symptoms of the conditions that ultimately caused the extinction."
My money's on the rest of the animals being inconsolably weirded out by bizarre mollusk mating habits.