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Younger Dryas meteorite impact theory consolidated

20 Sep
The revealing micro-spherules
After sometimes heated debates, it seems that the theory of a meteorite impacting on Earth, probably above Canada, at the beginnings of the Younger Dryas and probably related to megafauna extinctions seems to be gaining more and more weight.
Malcom A. LeCompte et al. Independent evaluation of conflicting microspherule results from different investigations of the Younger Dryas impact hypothesis. PNAS 2012. Pay per view (for 6 months/depending on world region) ··> LINK [doi]

Abstract

Firestone et al. sampled sedimentary sequences at many sites across North America, Europe, and Asia [Firestone RB, et al. (2007) Proc Natl Acad Sci USA 106:16016–16021]. In sediments dated to the Younger Dryas onset or Boundary (YDB) approximately 12,900 calendar years ago, Firestone et al. reported discovery of markers, including nanodiamonds, aciniform soot, high-temperature melt-glass, and magnetic microspherules attributed to cosmic impacts/airbursts. The microspherules were explained as either cosmic material ablation or terrestrial ejecta from a hypothesized North American impact that initiated the abrupt Younger Dryas cooling, contributed to megafaunal extinctions, and triggered human cultural shifts and population declines. A number of independent groups have confirmed the presence of YDB spherules, but two have not. One of them [Surovell TA, et al. (2009) Proc Natl Acad Sci USA 104:18155–18158] collected and analyzed samples from seven YDB sites, purportedly using the same protocol as Firestone et al., but did not find a single spherule in YDB sediments at two previously reported sites. To examine this discrepancy, we conducted an independent blind investigation of two sites common to both studies, and a third site investigated only by Surovell et al. We found abundant YDB microspherules at all three widely separated sites consistent with the results of Firestone et al. and conclude that the analytical protocol employed by Surovell et al. deviated significantly from that of Firestone et al. Morphological and geochemical analyses of YDB spherules suggest they are not cosmic, volcanic, authigenic, or anthropogenic in origin. Instead, they appear to have formed from abrupt melting and quenching of terrestrial materials.

Most interesting in this research is that it was done directly at an archaeological layer of the Clovis clulture, what makes the chronology very solid.

Also the authors claim that some of the negative reports did not follow the protocol to detect the spherules and that is why they missed them, stirring controversy.

Partial source: Science Daily.

See also for background (this blog and its predecessor in reverse chronological order):

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19 responses to “Younger Dryas meteorite impact theory consolidated

  1. terryt

    September 21, 2012 at 4:50 am

    "After sometimes heated debates, it seems that the theory of a meteorite impacting on Earth, probably above Canada, at the beginnings of the Younger Dryas and probably related to megafauna extinctions seems to be gaining more and more weight.After sometimes heated debates, it seems that the theory of a meteorite impacting on Earth, probably above Canada, at the beginnings of the Younger Dryas and probably related to megafauna extinctions seems to be gaining more and more weight". As far as I'm aware there has been no debate as to whether or not a meteorite hit at that time. The debate is over how great an effect it had on the fauna and flora of North America, and how widespread that effect was. The extinction at the time was very selective and so is unlikely to have been the product of a meteor impact, although I grant it may have reduced population size. However it should not have affected the recovery of the flora and fauna in the slightest. Something else held that recovery up.

     
  2. Maju

    September 21, 2012 at 8:43 am

    That may be your debate or greatest concern but the actual debate was about the impact happening or not at all. See the "see also" section for background: some researcher failed to find any micro-spherules and caused the initial theory to be doubted, with some heated debate after it. Nowadays however it seems consolidated.

     
  3. andrew

    September 21, 2012 at 5:04 pm

    The study certainly firms up this data point, in terms of the cause of the Younger Dryas and in terms of its relative temporal relationship to the Clovis culture.It suggests that something very different was going on in the pre-YD migration into the Americas of the earliest indigenous Americans and the modestly later Clovis expansion. Perhaps the initial human population of North America was exclusively via a Pacific coast route and the passage across Canada was accessable for large scale migration that opened the door to a subsequent east to west expansion of the Clovis people only after YD. It also suggests that the process at work in American megafauna extinctions may have been fundamentally different in North America where inter-related YD and Clovis expansion processes culminated in the rapid slaughter on North American mammals from the megafauna extinctions in South America (especially east of the Andes), where it may have been incident to the expansion of the human range into the area that may have been more gradual.

     
  4. Maju

    September 21, 2012 at 6:15 pm

    I did not think it would come up but it was also briefly mentioned in this blog that Clovis culture may well have ended for reasons other than the impact. In any case, Clovis pre-dates the impact, no gate was opened for them by the meteorite. Instead the meteorite, or rather the subsequent rapid climatic changes (in America as in Eurasia and elsewhere) are surely an important part explaining the extinction of megafauna in that period.

     
  5. terryt

    September 22, 2012 at 2:30 am

    "Instead the meteorite, or rather the subsequent rapid climatic changes (in America as in Eurasia and elsewhere) are surely an important part explaining the extinction of megafauna in that period". No, a completely inadequate explanation for the extinction.

     
  6. Maju

    September 22, 2012 at 3:05 am

    In Europe at least the first warming caused expansion of forest, what harmed the steppe beasts, like the mammoth, while the sudden freezing in a matter of months of the YD must have totally dislocated the survival mechanisms of most species, humans included. If that's not a extinction factor, then what is it?Notice that I'm never saying it was the only factor but an important one.

     
  7. terryt

    September 23, 2012 at 1:11 am

    "In Europe at least the first warming caused expansion of forest" We've been through the most likely reason for that, so I don't want to waste my time.

     
  8. terryt

    November 16, 2012 at 4:41 am

     
  9. dent10

    December 8, 2012 at 4:41 pm

     
  10. terryt

    December 10, 2012 at 8:53 am

     
  11. Maju

    December 10, 2012 at 10:29 am

     
  12. Maju

    December 10, 2012 at 10:29 am

     
  13. terryt

    December 11, 2012 at 12:17 am

     
  14. terryt

    December 11, 2012 at 1:09 am

     
  15. terryt

    December 11, 2012 at 1:10 am

     
  16. Maju

    December 11, 2012 at 3:50 am

     
  17. terryt

    December 12, 2012 at 8:49 am

     
  18. Maju

    December 12, 2012 at 9:54 am

     
  19. terryt

    December 13, 2012 at 9:44 am

     

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