Freethought & Rationalism Archive

ps418 · 06-13-2003, 06:46 AM

There is a report in the new Science outlining very good evidence for a middle-Devonian impact from a section in Morroco. I say the evidence is very good becasue of multiple, independent indications of impact: shocked quartz, microspherules with a strong chondritic geochemical signature, as well as coincidence with a signficant extinction event and a large stable isotope excursion.

Quote:

We have found evidence for a bolide impacting Earth in the mid-Devonian (380 million years ago), including high concentrations of shocked quartz, Ni, Cr, As, V, and Co anomalies; a large negative carbon isotope shift (�9 per mil); and microspherules and microcrysts at Jebel Mech Irdane in the Anti Atlas desert near Rissani, Morocco. This impact is important because it is coincident with a major global extinction event (Kac�k/otomari event), suggesting a possible cause-and-effect relation between the impact and the extinction. The result may represent the extinction of as many as 40% of all living marine animal genera.

Ellwood et al, 2003. Impact Ejecta Layer from the Mid-Devonian: Possible Connection to Global Mass Extinctions. Science 300, pp. 1734-1737.

Patrick

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