Scientist Sophie Newbury studies the "dead zone," a rock layer in Karoo Basin. Click on image for full size (97 Kb) Courtesy of Robert Gastaldo, Colby College

A paper reporting the results by Gastaldo, South African scientist Johann Neveling, and two 2008 Colby undergraduate students, C. Kittinger "Kit" Clark and Sophie Newbury, appears in the March 2009 issue of GEOLOGY.

Tens of millions of years before dinosaurs roamed Earth, their ancestors were all but eliminated in a catastrophic event called the Permian Mass Extinction. The Permian period extended from 299 to 252.6 million years ago.

"The Permian-Triassic boundary marks the greatest extinction event in Earth's history, with significant loss of biodiversity both on land and in the oceans," says H. Richard Lane, a paleontologist and program director in the National Science Foundation (NSF)'s Division of Earth Sciences, which funded the research.

"Until this study, it was believed that the event was marked by unique rocks traceable across southern hemisphere continents. This research calls into question whether the extinction event is actually constrained in the geologic record on land."

Ideas about the event's impact on land animals and plants are based largely on records in the Karoo Basin in central South Africa, where the best fossil records from that time are found, and where Gastaldo and his students have worked since 2003 with funding from NSF.

Earlier analysis of the rock record by other scientists working in South Africa led them to hypothesize about the nature, scope and timing of the mass die-off of prehistoric amphibians and reptiles.

They claimed that one unique sedimentary layer in the Karoo Basin overlies fossils of the last reptiles of the Permian period (synapsids, including the genus Dicynodon).

This layer has been dubbed "the dead zone" because of its absence of fossil remains.

This dead zone was thought to be synchronous in time and space, marking the event across southern Africa and as far away as Antarctica.

Now Gastaldo and co-authors report that they have found conflicting stratigraphic evidence in the Karoo Basin.

They discovered that this dead zone layer, or event bed, is not found at the same physical position in the rock record at all places, even across the immediate landscape where it was first described.

As such, it is not a reliable marker of the mass extinction of terrestrial animals, Gastaldo says.

Within one kilometer, just across the valley from the site where it was first described, the layer occurs lower in the rock record by eight meters (more than 25 feet).

Several hundred kilometers away, at Lootsberg Pass, reptile fossils occur above the layer rather than below it, further undermining the credibility of the zone as a marker of the mass extinction of animals at the end of the Permian.

Gastaldo says that the research proves that "there is no evidence to support a terminal extinction event in the record of the Karoo Basin, based on the criterion of an unique event bed or dead zone."

Text above is courtesy of the National Science Foundation

Scientist Sophie Newbury studies the "dead zone," a rock layer in Karoo Basin. Click on image for full size (97 Kb) Courtesy of Robert Gastaldo, Colby College

Geologists have made some discoveries that call into question popular theories about this Extinction.

Before, scientists thought they had found a distinct record of the Permian Mass Extinction in sedimentary rocks found across southern hemisphere continents. There was actually a layer in the rocks that scientists called the "dead zone" because of the lack of plant and animal fossils found there.

But recent work done in the Karoo Basin in central South Africa, where the best fossils records from the Permian time period are found, shows conflicting evidence in the layers of rock found.

They discovered that this dead zone layer is not found at the same physical position in the rock record at all places, even across a land area 1 kilometer across. As such, it is not a reliable marker of the mass extinction of terrestrial animals.

Lead geologist on this project, Robert Gastaldo, says that the research proves that "there is no evidence to support a terminal extinction event in the record of the Karoo Basin, based on the criterion of an unique event bed or dead zone."

Scientist Sophie Newbury studies the "dead zone," a rock layer in Karoo Basin. Click on image for full size (97 Kb) Courtesy of Robert Gastaldo, Colby College

Geologists thought they had found a layer in rock that showed this Permian Mass Extinction. This was a layer in the rock where there was a lack of plant and animal fossils. They even called the layer the "dead zone".

But recent work done in South Africa, where the best fossils records from the Permian time period are found, showed that this dead zone layer in this area of South Africa couldn't be a marker for the Permian Mass Extinction.

Science is about testing ideas. It's exciting to find that an idea is right, but sometimes scientists find out that an idea is wrong. Then, with even more knowledge in hand, it's back to the workbench to test new ideas!