When bivalves ruled the world( Before the worst mass extinction of l...)

Before the worst mass extinction of life in Earths history 252 million years ago ocean life was diverse and clam-like organisms called brachiopods dominated. After the calamity, when little else existed, a different kind of clam-like organism, called a bivalve, took over.

What can the separate fates of these two invertebrates tell scientists about surviving an extinction event"

A lot, says UWM paleoecologist Margaret Fraiser. Her research into this particular issue not only answers the question; it also supports a relatively new theory for the cause of the massive extinctions that occurred as the Permian period ended and the Triassic period began: toxic oceans created by too much atmospheric carbon dioxide (C02).

The theory is important because it could help scientists predict what would happen in the oceans during a modern C02 event. And it could give them an idea of what recovery time would be.

Studying the recovering ecology is equally significant, says Fraiser. The evolution of surviving species in the aftermath of the mass extinction set the stage for dinosaurs to evolve later in the Triassic.

From air to water Fossil records suggest that trauma in the oceans actually began in the air.

Estimates of the C02 in the atmosphere then were between six and 10 times greater than they are today, says Fraiser, an assistant professor of geosciences. It makes sense, she says. The largest continuous volcanic eruption on Earth known as the Siberian Traps had been pumping out C02 for about a million years prior to the Permian-Triassic mass extinction.

The Permian-Triassic extinction wiped out 70 percent of life on land and close to 95 percent in the ocean nearly everything except for bivalves and a fewer number of gastropods (snails).

C02 is a greenhouse gas that influences global temperatures. But, says Fraiser, according to the fossil record, high levels of C02 and the correspondingly
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