Bio Evidence for TJ Extinction

The authors note that "the release of CO2 from the outgassing of a large volume of basaltic lava has been cited as triggering an interval of intense greenhouse warming that resulted in a mass extinction at the Triassic-Jurassic boundary (200 million years ago)," citing the studies of Yapp and Poths (1996), McElwain et al. (1999) and McHone (2003), and they write that "similar transient increases in paleo-pCO2 have been identified at other important paleontologic boundaries using fossil stomatal data, including the Permian-Triassic (250 million years ago) and the Cretaceous-Tertiary (65 million years ago)," citing the work of Retallack (2001) and Beerling et al. (2002). However, they report that in addition to releasing CO2 into the air, "large flood basalt eruptions may include the loading of the atmosphere with SO2," which could also produce mass extinctions. Hence, they decided to collect a set of real-world measurements designed to determine if elevated concentrations of atmospheric SO2 can lower plant stomatal index in the same way that elevated concentrations of CO2 do, which if found to be the case would imply that calculations of pCO2 based on the stomatal frequency of fossil leaves may actually be due in large part to SO2, implying lower concentrations of atmospheric CO2 during past mass extinction events, which would imply less intense greenhouse warming and possibly reveal SO2 to be the primary culprit behind the mass die-offs.

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Tanner et al. measured the stomatal index (SI) of the common swordfern (Nephrolepis exaltata) in various plumes of actively outgassing vents of Kilauea, a basaltic shield volcano on the southeastern flank of Hawaii, as well as in other locations chosen in such a way as to provide situations where CO2 was high and SO2 low, where CO2 was low and SO2 high, and where both CO2 and SO2 were either high or low together.

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Tanner et al. conclude that "long-term eruptions may have produced a similar phenotypic response in plant species across large areas of the globe that is indistinguishable from that produced by elevated CO2." As a result, they further conclude that it is "necessary to examine more closely the impact of volcanogenic SO2 on the global environment and the potential role of SO2 outgassing as a mechanism of extinction."

hmmm. Interesting. Plants respond to SO2 similiarly as to elevated CO2. It would be interesting to see if there was a similar response among those critters that are supposed to be vulnerable to SO2 poisoning - like amphibians - to see if there was a die back at the same time. If not there might be a small issue here. Or it might be a way to differentiate the exact mechanism between CO2 and SO2 from flood basalts.