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Re: extinction

David Marjanovic wrote on 5 Jan 2004 the following response to Endre Simonyi's 30 Dec 2003 post:

Andre said:

Iridium itself may have played a significant role though, since while it is hardly oxidizable, it still does form compounds in other ways. (Materials in the sea, especially when taking the long period of time into consideration, might have dissolved iridium and as a result it became much more active).

David said:

Please be more specific. Suggest a specific mechanism, or this hypothesis is
untestable, therefore unscientific and must be _ignored_ by scientists.

New information on this topic can be found in a paper by Zhao et al. titled "A possible causal relationship between extinction of dinosaurs and K/T iridium enrichment in the Nanxiong Basin, South China: evidence from dinosaur eggshells" (Palaeogeography, Palaeoclimatology, Palaeoecology, 2002, v. 178, pp. 1-17).

The authors indicate that iridium and other trace element buildup in the environment, and consequently in dinosaur tissues, likely caused pathological thicknesses in dinosaur eggs, and microstructural alterations of the eggshells. Because multiple iridium spikes were distributed over a temporally long Cretaceous-Tertiary duration, they indicate also that the source of the iridium was likely the Deccan Traps volcanism, and not an asteroid impact.

For the record, I first linked the Deccan Traps volcanism to the K-T iridium enrichment, and mantle-degassing CO2-induced greenhouse, at the 1981 AAAS 147th National Meeting in Toronto, Canada. The K-T impact versus Deccan Traps extinctions debate began at the 1981 K-TEC II (Cretaceous-Tertiary Environmental Change) meeting in Ottawa, Canada, where I first encountered the Alvarez impact team.

Dewey McLean