Pre-dinosaur extinction killed 95% of sea species

It may never be as well known as the Cretaceous extinction, the one that killed off the dinosaurs. Yet the much earlier Permian extinction – 252 million years ago – was by far the most catastrophic of the planet’s five known paroxysms of species loss.

No wonder it is called the Great Dying: Scientists calculate that about 95 percent of marine species, and an uncountable but probably comparable percentage of land species, went extinct in a geological heartbeat.

The cause or causes of the Permian extinction remain a mystery. Among the hypotheses are a devastating asteroid strike, as in the Cretaceous extinction; a catastrophic volcanic eruption; and a welling-up of oxygen-depleted water from the depths of the oceans.

Now, painstaking analyses of fossils from the period point to a different way to think about the problem. And at the same time, they are providing startling new clues to the behavior of modern marine life and its future.

In two recent papers, scientists from Stanford and the University of California, Santa Cruz, adopted a cellular approach to what they called the “killing mechanism”: not what might have happened to the entire planet, but what happened within the cells of the animals to finish them off.

Their study of nearly 50,000 marine invertebrate fossils in 8,900 collections from the Permian period has allowed them to peer into the inner workings of the ancient creatures, giving them the ability to describe precisely how some died while others lived.

”Before, scientists were all over the map,” said one of the authors, Matthew E. Clapham, an earth scientist at Santa Cruz. “We thought maybe lots of things were going on.”

Clapham and his co-author, Jonathan L. Payne, a Stanford geochemist, concluded that animals with skeletons or shells made of calcium carbonate, or limestone, were more likely to die than those with skeletons of other substances. And animals that had few ways of protecting their internal chemistry were more apt to disappear.

Being widely dispersed across the planet was little protection against extinction, and neither was being numerous. The deaths happened throughout the ocean. Nor was there any correlation between extinction and how a creature moved or what it ate.

Instead, the authors concluded, the animals died from a lack of dissolved oxygen in the water, an excess of carbon dioxide, a reduced ability to make shells from calcium carbonate, altered ocean acidity and higher water temperatures. They also concluded that all these stresses happened rapidly and that each one amplified the effects of the others.

Alanna Mitchell, The New York Times, 1 May 2012. Full article.


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