Evolution’s ‘Big Bang’ Links Global Warming to Mass Extinctions

Glaciermelt To understand the fossil record and the diversity at any given time, scientists need to gain insight into conditions and match them up with the fossil record.

Greg Retallack of the University of Oregon in Eugene suggests that climate, and specifically global warming, may have contributed to fossil preservation. Retallack scanned through a database of 500 million years’ worth of fossils and found 41 individual episodes of “exceptional preservation” of organisms such as fish, crustaceans, insects and starfish scattered throughout the world. 

Retallack took those 41 locations, including well-known sites such as the 508-million-year-old Burgess Shale in Canada and the 123-million-year-old Liaoning site in China, and compared them to climate records over the same time periods. He found that during each peak in the fossil record, there was a corresponding spike in atmospheric carbon dioxide and methane levels, and a spike in precipitation levels and temperatures. It appears, he said, that “greenhouse episodes” may have occurred simultaneously with the mass extinctions.

But the question remains whether the greenhouse gas episodes preserved the fossils, or whether the episodes simply killed many life forms and thus left more to be preserved. “With a mass kill, there’s obviously a better chance of preservation because scavengers are overwhelmed, and they can’t completely recycle or consume” the bodies, said Raymond Rogers, a geologist at Macalester College in St. Paul, Minn. 

The dinosaur record from Madagascar, for example, has shown a strong correlation to climate, Rogers says. In a 15-meter-thick section of rock that contains several distinct dinosaur bonebeds, Rogers and colleagues found evidence of recurring severe droughts followed by extreme rainy periods that promoted burial — a link between climate conditions, mass death and preservation. 



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