Moose, from your source ;
Permian-Triassic extinction, about 251 million years ago. Many scientists suspect a comet or asteroid impact, although direct evidence has not been found. Others believe the cause was flood volcanism from the Siberian Traps and related loss of oxygen in the seas. Still others believe the impact triggered the volcanism and also may have done so during the Cretaceous-Tertiary extinction. The Permian-Triassic catastrophe was Earths worst mass extinction, killing 95 percent of all species, 53 percent of marine families, 84 percent of marine genera and an estimated 70 percent of land species such as plants, insects and vertebrate animals.
My point is that direct evidence has been found, recently, within the last 5-6 years.
Secondly, before anyone gets excited, flood volcanism refers to lava, not water.
I realise I was a bit absolute in saying that the P-T extinction was attributed to bolide impact. What I SHOULD have said was, there is now evidence of global effects caused by bolide impact, which in conjunction with other factors may have lead to the extinction.
I repeat the link here,
http://www.gsajournals.org/gsaonline/...{Shortened display form of URL, to restore page width to normal. At this time, the link seems to no longer point to the material it once did. - Adminnemooseus}
From the above link ;
Possible sources of isotopically light Sr for marine sediments include volcanic gas, Sr dissolved from the seafloor hydrothermal system, and ejecta from the mantle. Volcanic gas can be ignored quantitatively. An increase in dissolved Sr from the seafloor hydrothermal system leads to a decrease in the 87Sr/86Sr of seawater (87Sr/86SrHOAC-leachate). An increase in ejecta from the mantle causes a decrease in 87Sr/86Sr of clastics (87Sr/86SrHCl-residue initial) and no decrease in 87Sr/86Sr of seawater, because most of the Sr in ejecta do not dissolve in water. Therefore, a negative shift of 87Sr/ 86SrHCl-residue initial and the absence of a negative shift of 87Sr/86SrHOAC-leachate indicate that the source of light Sr was ejecta from the mantle. Rapid supply of mantle material agrees with the other evidence of an extraterrestrial impact and the decrease in sulfate sulfur isotope ratios, which leads to our conclusion that a rapid release of an enormous volume of sulfur from the mantle to the ocean-atmosphere system occurred as a result of the impact.
Indicating materials from the mantle WERE involved, if only as a result of the impact.
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Occam's razor is not for shaving with.
This message has been edited by Adminnemooseus, 11-26-2005 12:56 PM
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