I came across this interesting paper in a Geological Journal in 2005 that outlines a theoretical argument for how hydrogen sulphide might have been responsible for the Permian extinction event (Massive release of hydrogen sulfide to the surface ocean and atmosphere during intervals of oceanic anoxia).Simple calculations show that if deep-water H2S concentrations increased beyond a critical threshold during oceanic anoxic intervals of Earth history, the chemocline separating sulfidic deep waters from oxygenated surface waters could have risen abruptly to the ocean surface (a chemocline upward excursion). Atmospheric photochemical modeling indicates that resulting fluxes of H2S to the atmosphere (>2000 times the small modern flux from volcanoes) would likely have led to toxic levels of H2S in the atmosphere.
What I thought was interesting is that paper just predated the biomarker evidence I mentioned in class. They add this note in at the end of the paper:
Note Added in Proof: Biomarker evidence consistent with the hypothesis of chemocline upward excursion at the Permian-Triassic boundary has just been reported online in Science Express (Grice et al., 2005).
It must be kind of cool to have evidence for your theory come out just as your paper is being published.
Or maybe it was an asteroid. This is the recently discovered asteroid impact evidence I was trying to remember. It was from 2006. Scientific American had a 2006 article that reviewed the evidence for the alternative, although not necessarily mutually exclusive, theories.