[SunkenCiv]

PopSci for March 2004 (p 56) had a Dawn Stover piece on the Permian-Triassic extinction. She's got a table showing four possibilities and a summary of points for each, and also writes that "it's possible that more than theory is correct." A huge impact on water would send a shockwave throughout the oceans and seas, with the potential of releasing the methane in gas hydrates and the poisonous hydrogen sulfide gas that displaces oxygen in the depths. She ignores that likelier possibility and writes instead that an impact could trigger volcanic eruptions, "which in turn could have kicked off deadly acid rain showers."

The Suspect	The Theory	The Evidence	The Proponents	The Holes
Asteroid impact	A space rock strikes in the tropics, spews debris into the air and triggers lethal climate change	Scientists found 250 million year old rocks from Antarctica and China said to contain meteorite fragments	Researchers at the University of Rochester, Harvard, and UC Santa Barbara	Scientists have yet to find the ultimate smoking gun, a crater
Sudden methane explosion	A massive cloud of methane gas abruptly bursts from the ocean, cataclysmic flooding and fires ensue	Great Dying fossils show a sudden sharp rise in carbon-12 isotopes, best explained by a methane belch	Chemical engineer Gregory Ryskin at Northwestern University	The explosion requires an improbable 10,000 gigatons of methane
Slow methane leak	Volcanoes of frozen deposits leak methane over thousands of years, depleting oxygen	The burrowing reptile Lystrosaurus, adapted for low-oxygen conditions, thrived during this period	Researchers at the University of Oregon, the South African Museum, and the University of Washington	The leak could not deplete enought oxygen to cause global death, critics say
Hydrogen sulfide stink bomb	Lethal levels of hydrogen sulfide, emitted by anaerobic bacteria, are expelled from the ocean into the air	Proponents are searching for signs of sulfur bacteria in Japanese sediments dated to the extinction	Scientists at Penn State, the University of Colorado, and the University of Tokyo	There's no proof that the upper layers of ancient oceans were devoid of oxygen

My guess is, Dawn Stover went to Penn State and studied volcanology for a while. ;')

[SunkenCiv]

Meteor May Have Started Dinosaur Era
by Kenneth Chang
May 17, 2002

In the layer of rock corresponding to the extinction, the scientists found elevated amounts of the rare element iridium. A precious metal belonging to the platinum group of elements, iridium is more abundant in meteorites than in rocks on Earth. A similar spike of iridium in 65 million-year-old rocks gave rise in the 1970's to the theory that a meteor caused the demise of the dinosaurs... The levels are only about one-tenth as high as those found at the later extinction. That could mean that the meteor was smaller or contained less iridium... In the same rock layer, Dr. Olsen and his colleagues found a high concentration of fern spores -- considered an indicator of a major disruption in the environment. Because spores carried by the wind can travel long distances, ferns are often the first plants to return to a devastated landscape. The scientists found more evidence of rapid extinction in a database of 10,000 muddy footprints turned to rock in former lake basins from Virginia to Nova Scotia... Because the sediment piles up quickly in lake basins, the researchers were able to assign a date to each footprint, based on the layer of rock where it was found. They determined that the mix of animals walking across what is now the East Coast of North America changed suddenly about 200 million years ago. The tracks of several major reptile groups continue almost up to the layer of rock marking the end of the Triassic geologic period 202 million years ago, then vanish in younger layers from the Jurassic period...