Clams and Snails Provoked the Greatest Mass Extinction Ever!

The most famous mass extinction is perhaps that of the dinosaurs, 65 million years ago. The current man made extinction could be even worse. And several mass extinctions occurred along the geological eras.

But the dinosaur extinction could be a minor event compared to what the clumsy snails and clams did 250 million years ago: they wiped out 95 % of the Earth species during the end-Permian mass extinction.

A new study shows that the disaster was long in coming, not triggered by a catastrophic extraterrestrial event such as an asteroid impact that finished off the dinosaurs. The Permian mass extinction installed the rule of oysters, snails and shelled cephalopods. Studying the Permian fossils, researchers have found that the mollusks began rising to prominence some 8 million years before the end-Permian extinction.

"Our results aren't really consistent with a more catastrophic extraterrestrial cause, such as an asteroid impact - although they don't directly contradict the impact theory either," said researcher Matthew Clapham at Queen's University in Kingston, Canada.

The study enhances the hypothesis of "the climax of a prolonged environmental crisis," Clapham said.

During the Permian period, 300 to 250 million years ago, a gradual warming of the planet took place. This warming slowed down ocean circulation, determining very low oxygen levels in the water. Massive volcanic eruptions to the end of the Permian further worsened the conditions.

"Mollusks are better adapted to such stressful and changing environments, and so could have thrived," Clapham told LiveScience.

"The abundance of mollusks we see are symptoms of the conditions that ultimately caused the extinction."

The 4 years research meant the investigation of 33,000 Permian fossils from blocks of limestone coming from China, Greece, Thailand, Nevada and Texas over the course of four years. The limestone blocks were sunk in vats of hydrochloric acid. The acid dissolved the limestone, but as the fossil shells were made of silica (this chemical replaces the original components in fossil bones and shells), which is unbreakable by the acids, they resisted to the acid action.

"Most of the fossils were less than one centimeter in size, typically 4 to 8 mm [roughly the size of an ant], so it was very delicate work to find them among all of the other detritus in the sample," said Clapham.