Cincinnati -- Whatever caused the world's largest mass extinction event apparently did not play favorites.
University of Cincinnati graduate student Stewart Ebersole and Arnold Miller, professor of geology at UC, will report Wednesday, Oct. 30 during the annual meeting of the Geological Society of America that the Late Permian mass extinction was global in its extent and hit all marine areas with roughly the same effect.
Traditionally, geologists believed that tropical areas and high-diversity marine environments such as reefs were hit hardest during mass extinction events. Cooler areas of the globe and polar regions appeared to be spared the most dramatic effects of mass extinctions.
However, when Ebersole and Miller examined data on articulate brachiopods, which were diverse groups at the time, they found no trend at all. "Early on, I expected to see that the tropics would be smashed," explained Ebersole. "But extinction rates were consistent from pole to pole. All the areas were being hit in a similar manner."
To conduct his analysis, Ebersole compiled a database of nearly 3,000 occurrences of articulate brachiopods. This group was among the hardest hit during the extinction event. "They go from super diverse to almost nothing," said Ebersole . "So, they make a very good candidate for studying global trends in extinction."
Ebersole looked for trends in two places. First, he split up the fossil occurrences according to the geographic region in which they were found during the Permian. This allowed him to determine whether one region was hit harder than another. His analysis showed no clear difference among regions. Temperate areas were hit just as hard as tropical ones.
Secondly, he looked at distinct environmental zones from near shore to deep water. Reefs and other highly diverse environments generally occur within a specific environmental zone. Again, there was no significant difference among zones. The Late Permian extinction event affected them all equally.
As a continuation of his research, Ebersole will extend his analysis to do a latitude by latitude comparison. He expects that will provide additional evidence in favor of a long-term, global cause for the massive die-off.
"There's something worldwide going on," insisted Ebersole . "No one's really been able to find a cause for the Late Permian extinction, but this restricts the cause to something with a globally consistent mechanism. It's a really exciting finding."
Ebersole said his results are similar to the earlier findings by David Raup and David Jablonski on the extinction of molluscs in the Late Cretaceous. Raup and Jablonski also found no significant differences in extinction rates from one region to another.