Thursday 20 September 2012

The YD Boundary Impact Theory is Back in Business!

Impact. Source: (via
Who could have predicted? News from has it that there are oodles of microspherules in the Y-D boundary sediments throughout NA--it's just that previous workers were missing them. Marco Lambroek? Over to you? As I've said before, I find impacts very seductive, especially when they might help to explain mysterious disappearances of fauna--such as the Permian and K-T mass extinctions. A series of articles back in the early days of The Subversive Archaeologist heralded this story--beginning here. This one, the Younger Dryas in North America, isn't going away. Hat tip to Mark Collard for bringing this to our attentions.

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  1. I've read the PNAS paper and I have these points to make:

    1) they find that soil directly below artifacts yield less spherules: the argument is that the artifacts shielded the soil underneath them from spherules.

    I find this to be an extraordinary case of the Pompeii Premise. They assume the artifacts didn't move an inch after initial deposition. As we all know, that is highly unlikely.

    2) the amount of spherules per sediment unit for YD and post-YD (early Holocene) sediments are not much different, looking at their tables. I do not see a clear, statistically significant concentration at the YD levels.

    This then begs the question: what are these spherules if they are present in post-YD sediment as well in numbers that do not appear to be much different from their occurrence in YD sediments?

    The point being of course: if these are impact-generated spherules (as they argue, from morphological criteria), they should only be present in significant numbers in YD levels, not in early Holocene levels as well.

    3) nowhere in the study is the potential influence of differences in sedimentation rate seriously discussed.

  2. Hi, Marco,
    As was the case in early 2012, your comments are well considered and appreciated! I really have to wonder why I did so poorly in the academy when it's evidently possible to get published in prestigious journals with little but assertion to support a thesis. But, as I've said before, I'm not bitter.

  3. Rob, the assertion that an impact occurred at the Younger Dryas boundary is based upon meticulous proxy evidence, while Mr. Langbroek's assertions are baseless.

    That being said, many do not believe an huge impact occurred at that time, but are engaged in the wild speculation necessary to make a big impact work at that time, and have actively located putative impact remnants that could explain the evidence we do see, and also the meticulous sediment analysis that would falsify the hypotheses. This is how science works. Mr. Langbroek would be well advised to attempt to learn something from failed hypotheses and their investigations.

  4. @ kT
    Jeepers! Don't sugar-coat it. Tell us how you really feel.

  5. Ok Rob, I feel that a cosmic impact in or near North America is neither necessary nor sufficient to explain megafaunal extinctions in North America, nor the climate reversal at the beginning of the Younger Dryas chronozone. On the other hand, if a big cosmic impact did occur at that time, I certainly would want to know about it (as in yes or no) and if the answer is yes, then where did it occur and what were its effects on both the environment and biota.

    Clear enough? It works for me. I'm also tangentially interested in this particular hypothesis from a purely psychological perspective as applied to both its supporters and detractors, as I'm always interested in the recognition threshold for emergent phenomena as spectroscopic resolution progresses. These kinds of events happen all the time in condensed matter physics, and theories and hypotheses fall by the wayside left and right without presenting any obvious trauma or schisms in their respective scientific domains. I've seen this happen with extrasolar planets, Mars water and now Mars life as well.


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