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Re: extinction

Response to Phil Bigelow's Wed, 14 Jan 2004 02:30:52 post.

Phil wrote: "as I understand it, iridium does not aerosolize out of basalt flows. In fact, iridium doesn't aerosolize at all. The chlorides, fluorides, and oxides of iridium (which have to be produced under laboratory conditions)
are all dense solids."

In 1983, Bill Zoller, Josef Parrington, and Janet Phelan Kotra published a milestone paper titled "Iridium enrichment in airborne particles from Kilauea volcano: January 1983" (Science, 1983) in which it was shown for the first time that volcanos can release iridium into the atmosphere. The authors stated, "The iridium enrichment appears to be linked with the high fluorine content of the volcanic gases, which suggest that the iridium is released as a volatile IrF6." Fluorine gases are found only in volcanoes fed by a deep magma source, possibly the mantle. And, "The calculated mass of Ir in the K/T boundary layer is approximately 200 kilotons and would require an eruption much larger...than Kilauea...the Deccan flood basalts...were of sufficient magnitude to have introduced the Ir found in the K-T layer."

In 1989, Toutain and Meyer published a paper titled "Iridium-bearing sublimates at a hot-spot volcano (Piton de la Fournaise, Indian Ocean)" (Geophysical Research Letters, 1989). They pointed out that iridium seems to be preferentially released by hot-spot type volcanoes. They also noted that Piton de la Fournaise is related to the hot-spot track which generated the Deccan Traps, and that volcanic gaseous iridium can be related to the KTB. And, that if investigations of the Deccan volcanics do not evidence significant iridium contents, it has been calculated that Ir amounts about three times less than iridium in lavas of Piton de la Fournaise (0.25±0.03 ppb) are sufficient to produce the KTB iridium anomaly (Rocchia et al. 1988).

In 1986, Olmez, Finnegan, and Zoller published a paper titled "Iridium emissions from Kilauea volcano" (Journal of Geophysical Research, 1986). Following is a direct quotation from the paper:

"...Kilauea is a small volcano with insignificant eruptions....To estimate the importance for the mass extinction hypothesis, one must consider eruptions of a much larger scale, such as those...65 m.y. ago. One such eruption has been discussed by McLean [1982], who believes that the Deccan Traps basalts were a likely candidate....The Deccan probably did not occur on a short time scale, but let us estimate the quantity of Ir that could be emitted if the emissions were Kilauea-like in nature. Since approximately 10 x 10^6 km^3 of magma were emitted by the Deccan, the Ir emissions would be expected to be of the order of 30,000 tons, a little less than the mass believed to be contained in the KT boundary layer."

Dewey McLean