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Thread: The Ediacaran extinction

  1. #1 The Ediacaran extinction 
    Forum Radioactive Isotope sculptor's Avatar
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    Anyone have information on The Ediacaran extinction?


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  3. #2  
    exchemist
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    Quote Originally Posted by sculptor View Post
    Anyone have information on The Ediacaran extinction?
    Well you could try this for a kick-off: http://www.palaeos.org/Ediacaran

    I read a popular science book called "Darwin's Lost World", by Martin Brasier, a specialist in this period, which speaks of a series of extremely severe glaciations, as evidenced by global presence of boulder beds, below the Ediacaran level and maybe above it too, though I am not sure whether this is reading what he says correctly. The Palaos article doesn't seem to mention a post-Ediacaran glaciation, and seems to say that whether or not there really was an extinction event is open to question. I'm not surprised. The enigmatic quality of these fossils and their extreme age evidently makes it hard to find locations where they remain preserved.

    I recall Brasier intriguingly theorises that the development of the mouth had a dramatic effect on life. Once the mouth appeared, organisms had to defend themselves from being captured and eaten, either by burrowing, thus disturbing the sediments and making trace fossils rarer, or by defensive armour, hence the famous "small shelly fossils" that characterise the pre-Cambrian after the Ediacaran.

    But I'm not an expert on all this.


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    Universal Mind John Galt's Avatar
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    Quote Originally Posted by sculptor View Post
    Anyone have information on The Ediacaran extinction?
    Sorry, everyone died.

    @exchemist - I'll second your recommendation of "Darwin's Lost World."

    Now sculptor, can you be a little more precise in your question? I can deluge you with references, but some filtering would be helpful.

    In the meantime, this is a good review paper on the Ediacara taxa.

    This one looks at the role of the assembly of Gondwana in the distribution of Ediacaran and Cambrian forms.

    This one on biogeochemical changes in the Neoproterozoic-Cambrian is just a good paper.
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  5. #4  
    Forum Radioactive Isotope sculptor's Avatar
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    Quote Originally Posted by John Galt View Post
    Quote Originally Posted by sculptor View Post
    Anyone have information on The Ediacaran extinction?
    Sorry, everyone died.
    Did they really?
    Therein lies the dilema.
    was there a snowball earth, or was g e williams correct in his postulation of a radical tilt.
    if williams was correct, what caused the obliquity of the ecliptic to exceed 54 degrees, and what mechanism returned us to the present obliquity?

    there is evidence that circa 8-900mybp the axial tilt was as per todays "normal" and many have disputed Williams' postulation
    there is also a compelling arguement that the ediacaran fauna did not suffer extinction as would be expected under a "snowball earth" but may have just been overwelmed by the cambrian explosion of "new" fauna.

    without something radical as in a bolide impact, the change in the obliquity would seem improbable, but not out of the question?

    (wild guess du jour) there was less landmass then, and little was equatorial, which would lead to support of williams' postulation?


    whither hence?
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    WYSIWYG Moderator marnixR's Avatar
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    correct me if i'm wrong, but the ediacaran fauna lived AFTER snowball earth ?
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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    Quote Originally Posted by marnixR View Post
    correct me if i'm wrong, but the ediacaran fauna lived AFTER snowball earth ?
    Cryogenian - Wikipedia, the free encyclopedia

    Ediacara biota - Wikipedia, the free encyclopedia

    The Ediacara biota radiated in an event called the Avalon Explosion, 575 million years ago,[1][2] after the Earth had thawed from the Cryogenian period's extensive glaciation.
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    Universal Mind John Galt's Avatar
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    Marnix is absolutely correct, as confirmed by Neverfly's links.

    Sculptor, you seem to be being cherry picking the research to find one dissenting voice, then presenting it as if we were faced with two equally viable alternatives. That is certainly not the case. In the first place the change of axial tilt is not a strong contender, for a variety of reasons. Secondly, the situation is a lot more complex than just those two alternatives: correlations of glaciations is difficult and disputed; the extent of each glacial episode is uncertain; the depositional environments of the relevant sediments is not clear cut.

    Note: My reading in this field is limited to around 100 papers and none of them are later than 2011. This could influence the accuracy of my statements above.
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  9. #8  
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    Marnix had a legitimate question, and neverfly's links are/were a good starting point for further investigations.

    Have you ever had the experience of staring intently at something, and the closer you look the more blurred the image?

    Early on, in my readings, the ediacaran did indeed seem to follow the Cryogenian(standard model), which hinges almost entirely on the concept of episodes of snowball earth, which would then lead to a seperate ediacaran microbiota following the cryogenian, which itself is disputed by williams. (momentarily ignoring logical feedback albedo loops)
    Throw into the mix, the work of Małgorzata Moczydłowska who found ediacaran microbiota within the assumed cryogenian, and the oft voiced claime that the cambrian explosion followed a period of global glaciation, which was disputed by Alexei Ivanov and associates.

    Which, is why I tried to phrase the questions more openly------at which, I seem to have failed to provide the platform for a more thorough examination of the disperate conclusions of the researched materials.
    Not the least of which is the attempts to locate continental locations based on assumed paleomagnetism.

    Originally, it seemed to me that williams' postulation(supported by jenkins-JGR-2012) was the sole "wild card" in this game, but as I read on, the deck seems to be full of partially legible "wild cards" whose precision defies unity within the deck.
    If the williams card turns out to be the one needed to fill in the royal flush, then we may kiss the cryogenic snowball earth models good-bye, so his postulation figgured strongly in my questions, but with the caveat that I've not found anything that would account for the radical axial tilt postulated by him. (save for a possible bolide encounter)

    ................
    as always
    whither hence?
    Last edited by sculptor; June 5th, 2013 at 12:58 PM.
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