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