The Permian—Triassic extinction event, informally known as the Great Dying,was an extinction event that occurred 250 million years ago, forming the boundary between the Permian and Triassic geologic periods. It was the Earth's most severe extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct. Researchers at the University of Calgary believe they have discovered evidence to support massive volcanic eruptions that burnt significant volumes of coal, producing ash clouds that had broad impact on global oceans. Interesting enough there is a "coal gap" from this era. Coal deposits dating from this time are few.
There are several proposed mechanisms for the extinction event, including both catastrophic and gradualistic processes. The former include large or multiple bolide impact events, increased volcanism, or sudden release of methane hydrates from the sea floor. The latter include sea-level change, anoxia, and increasing aridity. Any hypothesis about the cause must explain the selectivity of the event, which primarily affected organisms with calcium carbonate skeletons; the long (4-6 million year) period before recovery started; and the minimal extent of biological mineralization (despite inorganic carbonates being deposited) once the recovery began.
Trilobites are an example of a well-known fossil group of extinct marine arthropods. They flourished throughout the lower Paleozoic era before beginning a drawn-out decline to extinction when, during the Devonian, all trilobite orders, with the sole exception of Proetida, died out. Trilobites finally disappeared in the mass extinction at the end of the Permian about 250 million years ago.
The new research suggest that this is could be "...the smoking gun that explains the latest Permian extinction," says Dr. Steve Grasby, adjunct professor in the University of Calgary's Department of Geoscience and research scientist at Natural Resources Canada.
Grasby and colleagues discovered layers of coal ash in rocks from the extinction boundary in Canada's High Arctic that give the first direct proof to support this and have published their findings in Nature Geoscience.
Unlike the end of dinosaurs, 65 million years ago, where there is widespread belief that the impact of a meteorite was at least the partial cause, it is unclear what caused the late Permian extinction. Previous researchers have suggested massive volcanic eruptions through coal beds in Siberia would generate significant greenhouse gases causing run away global warming.
The Siberian Traps eruptions were formerly thought to have lasted for millions of years, but recent research dates them to 250 million years ago,
The Emeishan and Siberian Traps eruptions may have caused dust clouds and acid aerosols—which would have blocked out sunlight and thus disrupted photosynthesis both on land and in the photic zone of the ocean, causing food chains to collapse. These eruptions may also have caused acid rain when the aerosols washed out of the atmosphere. This may have killed land plants and molluscs and planktonic organisms which had calcium carbonate shells. The eruptions would also have emitted carbon dioxide, causing global warming.
"Our research is the first to show direct evidence that massive volcanic eruptions — the largest the world has ever witnessed —caused massive coal combustion thus supporting models for significant generation of greenhouse gases at this time," says Grasby.
At the time of the extinction, the Earth contained one big land mass, a supercontinent known as Pangaea. The environment ranged from desert to lush forest. Four-limbed vertebrates were becoming more diverse and among them were primitive amphibians, early reptiles and synapsids: the group that would, one day, include mammals.
The location of volcanoes, known as the Siberian Traps, are now found in northern Russia. They cover an area just under two-million-square kilometers, a size greater than that of Europe. The ash plumes from the volcanoes traveled to regions now in Canada's arctic where coal-ash layers were found.
Grasby studied the formations with Dr. Benoit Beauchamp, a professor in the Department of Geoscience at the University of Calgary. They called upon Dr. Hamed Sanei adjunct professor at the University of Calgary and a researcher at NRCan to look at some of peculiar organic layers they had discovered.
"We saw layers with abundant organic matter and Hamed immediately determined that they were layers of coal-ash, exactly like that produced by modern coal burning power plants," says Beauchamp.
Sanei adds: "Our discovery provides the first direct confirmation for coal ash during this extinction as it may not have been recognized before."
The ash, the authors suggest, may have caused even more trouble for a planet that was already heating up with its oceans starting to suffocate because of decreasing oxygen levels.
For further information: http://www.eurekalert.org/pub_releases/2011-01/uoc-rfs012111.php