Talk:Ordovician–Silurian extinction events
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khhg
You aren't combining the End Ordovician and End Silurian extinctions are you?
Dragons flight 23:03, Sep 19, 2004 (UTC)
To address Dragons flight's question, the end Ordovician extinction event began with a major glaciation which resulted in a major sea level drop (as much as 80 meters according to some sources). This resulted in a major extinction as continental shelves dried up and habitats changed or disappeared. Later, the glaciers melted, sea levels rose as high or even higher than they were before the glaciation, and the survivors of the first event were hit by another extinction event as environments and habitats changed yet again. All of this occured during the 1.9 million years of the Hirnantian stage.
My sources for this are The Great Ordovician Biodiversification Event, Edited by Barry Webby and Mary Droser, 2004, Columbia University Press; and A Geologic Time Scale 2004, Edited by Felix Gradstein, James Ogg, and Alan Smith, 2004, Cambridge University Press.
Hope this helps.
--Lenn 03:00, Jun 24, 2005 (UTC)
Hmm messing through the extinction events i have two remarks, the first being why is not immediatly the option of extraterrestial impact(s) , tested? I suppose it is, but i have read older reports telling most major extinction events have a Sr-rich layer right under. It would be relatively easy to establish and a rather telling fact for ppl like me (wogohob eg. first focusses on oceanographic aspects). A period of 1.6 million year for restabilisation of the ecosphere is somewhat high but nothing really exceptional. A severe event, upsets speciation for at least a million years, several severe events, as apparently geologically , paleologically proven in this case, would prolong that from the first occurence of the event to 1 million years after the last occurance. Ice ages have not as far as i know had any severe impact on diversity mondially. Ofcourse they might locally lead to cambrian circumstances, my bet would be eg. under the ice of antartica one could find confusingly cambrian-like geologys. Also if the effect was due 'natural' fluctuations of the earths circumstances several genera would hardly have been touched. Wich is according to the article not the case. Simple question, can we establish wether meteorite impact was the cause before hopefully shouting earths natural fluctuations may provide sufficient (lack of) CO2 for extinction? As an example , the broken up comet that hit jupiter, might have taken 2 passages before all parts hit jupiter(would that be 60ky or 600?).77.248.56.242 13:39, 2 July 2007 (UTC)
[edit] I'm sorry, speak into my good ear?
Scientists from the University of Kansas and NASA have suggested that the initial extinctions could have been caused by a gamma ray burst originating from an exploding star within 6,000 light years of Earth (within a nearby arm of the Milky Way Galaxy). A ten-second burst would have stripped the Earth's atmosphere of half of its ozone almost immediately, causing surface-dwelling organisms, including those responsible for planetary photosynthesis, to be exposed to high levels of ultraviolet radiation. This would have killed many species and caused a drop in temperatures [2]. While plausible, there is no unambiguous evidence that such a nearby gamma ray burst has ever actually occurred.
This is a very creative use of the word "plausible" since in fact this is not plausible at all. You tell me how plausible it is that a GRB occurred at exactly the right distance that it happened to kill a significant percentage of life on Earth without killing absolutely all of it forever. Do you know what the margin of error is on those two alternatives, in terms of a gamma ray burst? Insignificantly little. So this is only plausible if you consider "deus ex machina" to be an equally plausible alternative. --75.63.48.18 (talk) 17:09, 20 January 2008 (UTC)
