| No meteorite impact at the Frasnian-Famennian mass extinction |
| links: Gwyneth |
| A paper, by Gwyn Gordon with co-authors Matt Rockman (New York University), Karl Turekian (Yale) and Jeff Over (SUNY at Geneseo), appears in the May issue of the American Journal of Science ("Osmium Isotopic Evidence Against an impact at the Frasnian-Famennian boundary", AJS v. 309, p.420-430; doi:10.2475/05.2009.03). This paper demonstrates conclusively that there could not have been a global meteorite impact immediately prior or during this mass extinction boundary - one of the five largest in Earth's history. The paper examines two sites: one in upstate New York and the other in France. The upstate New York sequence measured ten depths below, at and above the boundary and derived an isochron that is consistent with other measurements of the boundary's age. This is the first direct measurement of osmium isotopes at the F-F boundary; the initial 187Os/188Os value of 0.49 ±0.16 is consistent with other estimates of marine Os isotopes for this period and demonstrates no indication of significant extraterrestrial material. Samples at La Serre, France, have highly enriched Os concentrations of greater than 33 ppb - the highest published Os concentrations for this boundary and more than two orders of magnitude higher than average shale - but the 187Os/188Os is highly radiogenic and indicates no addition of significant meteoritic material. |
| posted by gwyn on 2009-08-26 |
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