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News Release June 21, 2001
GSA Release No. 01-27
Contact: Christa Stratton

Mass Extinction At The Triassic-Jurassic Boundary: Where's The Smoking Gun?

Who did it? Who pulled the trigger, or rather, what pulled the trigger at the Triassic-Jurassic boundary that wiped out 20% of all marine families in Earth's oceans, and, on land, most non-dinosaurian archosaurs, most therapsids, and the last of the large amphibians? Whatever it was, it shot down much of the competition so dinosaurs could later dominate the Earth.

"The Triassic-Jurassic boundary extinction event is one of the 'big five' mass extinctions of the Phanerozoic Eon, profoundly affecting life on land and in the oceans," explained Lawrence Tanner, a Professor of Geography and Geoscience at Bloomsburg University in Pennsylvania. Tanner will shed light on the various extinction theories on Wednesday, June 27, at the "Earth System Processes" meeting in Edinburgh Scotland.

"Ultimately, this presentation concerns our ability to test various hypotheses for the cause of large-scale extinction events of the past," he said. Tanner will address possible explanations for this event. One is gradual climate change or sea-level change during the Late Triassic, but these explanations fail to explain the suddenness of the extinctions in the marine realm. Then there's; asteroid impact-however, no impact structure can be tied directly to the Triassic-Jurassic boundary. And the current favorite hypothesis is that flood basalts that constitute the Central Atlantic Magmatic Province erupted. And the release of CO2 or SO2 aerosols during these eruptions are thought to have caused intense global warming (from the former) or cooling (from the latter). But Tanner's new data on the isotopic composition of fossil soils of Late Triassic and Early Jurassic age demonstrates that there is no evidence of any change in the CO2 composition of the atmosphere. So the smoking gun still eludes scientists and the cause of this extinction is still at large. "Other possibilities need to be investigated more fully," Tanner explained.

The Geological Society of America and the Geological Society of London will co-convene the Earth Systems Processes meeting in Edinburgh, Scotland.


During the Earth System Processes meeting, June 25-28, contact the GSA/GSL Newsroom at the Edinburgh International Conference Centre for assistance and to arrange for interviews: +44 (0) 131 519 4134

Ted Nield, GSL Science and Communications Officer
Ann Cairns, GSA Director of Communications

The abstract for this presentation is available at:

Post-meeting contact information:

Lawrence Tanner
Dept. of Geography and Geosciences
Bloomsburg University
Bloomsburg, PA 17815 USA

Ted Nield
Geological Society of London
+44 (0) 20 7434 9944

Ann Cairns
Geological Society of America
+01 303 447 2020 ext. 1156

To view other Earth System Processes press releases, see

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