Big Burn: North American Great Plains fire layer re-proposed by Wisconson



A paper this week from the University of Wisconsin announces a predictable conclusion to readers of the Tusk: The transition from the Pleistocene to the Holocene is characterized by soil signatures of fire on a continental scale. The author’s geochemical analysis is helpful and welcome, but my children would have a pretty good shot at guessing what happened in olden days by simply looking at the photo above — Looks like there was a big fire, dad.

Equally obvious to me (perhaps not the kids) is the conspicuous absence of any citation to the Firestone papers. It would seem that multiple major journal publications providing much more detailed evidence of frightful temperatures and horrendous fires within the period of Marin-Spiotta et al.’s own study of the same region would merit a reference in support of their hypothesis. But alas and for shame it does not.

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  • Ed said “Your comment demonstrate your rather entirely complete ignorance of Gene Shoemaker’s life and and his work.“

    Your continued failure to provide any useful, or varifiable, information whatsoever beyond personal ad hominem insults is typical of you Ed. And this kind of childish fifth grade behavior is in fact the very reason George had to boot you from the Tusk.

    So what can we deduce about your own level of ignorance from the painfully obvious fact that you never learn?

  • Steve Garcia

    Dennis –

    The Rio Cuarto craters (however many of the toal regional elliptical crater-like features are accepted as actual impacts) can for the moment be positioned as one extreme shape of crater. Round impact craters represent the opposite pole of the range of crater-shaped impacts.

    We seem to be in a world where the experts on these shapes can’t accept much of anything but circular craters, which doesn’t make much sense. “YES, to all those that ARE circular”, they say, and no to any that are not.

    I would argue the opposite – that Rio Cuarto changed everything. I ask why, now that now that elliptical shapes are known to be craters, we have we gone over 20 years without finding any more?

    Elliptical shapes should be looked for in the geomorphology of the planet. If there is ONE Rio Cuarto event (even if RC would have been ONE crater, not 10), then there must be more. And the ellipticity of them is probably going to be different than Rio Cuarto. Given the extreme elongation there, one would expect the others to be less elongated.

    Somewhere along the way the intermediate elliptical shapes must be found and accepted.

    Rio Cuarto’s low angle of incidence does argue strongly for a long path in the atmosphere, both in kms and also in time. Longer deceleration means lower ground impact velocity. That SHOULD ALSO be a clue as to the different energy transfer to the target, which should also argue that the thinking that dictates all craters to be circular needs to be re-thought.

    In addition, if RC craters are low-velocity craters, then the other elliptical craters – when found – should be higher velocity, because they are most likely to be less elongated.

    SOMEWHERE along the velocity range, there must eventually be found a circular-to-elliptical transition. Rio Cuarto is certainly the low-velocity at the bottom of the range. At least for now. But how FAST might Rio Cuarto have impacted and still been elliptical?

  • jim coyle

    Steve; Here is one explanation of why craters are mostly round. (The explanation of this is that when an asteroid hits a planetary sized body, the initial crater (which may be elongated) is wiped out a few milliseconds later by the explosive release of kinetic energy. This explosion creates an essentially spherical impact feature.) This paragraph is from Dr Andrew Glickson’s article on the Mt Ashmore Impact Crater.

  • Steve, in the tests I did, even with a relatively slow veleocity impact, I could not get a nice, oval, crater at all.
    All of my shots, except for the very low angled ones, produced a fairly round depression at the point of impact. That thing that changed the most with changes in impact angle was the ejecta patterns. Where a butterfly pattern was the most common signature of a low angle shot. Instead of the oval crater one might intuitively expect.

  • jim coyle

    Gents; I’m not sure which thread to put this on so it goes here. It’s interesting to say the least.

  • jim coyle

    here’s another interesting video. I thought there would be a massive explosion but no! Now if you throw water or ice into lava—LOOK OUT!! Velly intellesting?

  • jim coyle
  • Steve Garcia

    Jim –

    On the lava-on-ice thing, cool – but I will try an off-the-cuff possibility to explain it:

    I am pretty sure the weight – AND VISCOSITY – of the lava is suppressing the ‘exploding water’ – but not completely. It is in all cases of resisting force-vs-expanding force. Notice the (mostly) large bubbles – evidently there is some of the water steaming up and expanding and with enough pressure to push up through the lava.

    SOME of the bubbles burst, but notice that that happens kind of in slow motion. Why? I think it could be because the higher the bubble rises the more the lava gets cooled by the steam (and abetted by the air right at the surface), so the lava is a bit more viscous on top, resisting even a bit MORE.

    When it is water on top, its weight is nothing close to being able to resist the expansion pressure/force, so it goes ‘nuclear’.

    This DOES perhaps have some application to a meteor impacting ice, so this is a good ‘get’ by you.