Comet Impact in the Pleistocene Era Led to an Abrupt Climate Change?

Imagine when the Earth awakened from the last Ice Age—but fell back into an icy slumber for another thousand years. That abrupt, climate scenario is known as the Younger Dryas event, and it is currently investigated by teams of researchers. One must note the scenario took place during humanity’s hunter-gathering adolescence. (There is a mainstream theory for the Younger Dryas event: rapid melt during de-glaciation altered temperatures of the Arctic Ocean, and the resulting temperature change of the Ocean altered weather patterns.)

However, there has been an alternative hypothesis given for the Younger Dryas event.

The term Younger Dryas is derived in part from the root, Dryas—which is an arctic-alpine flowering plant that flourished during the climatic upheaval. The geological interval of the Younger Dryas is often recognized as occurring during the Pleistocene era. The 1000 year interval witnessed the demise of the North American camel, the giant sloth, saber-toothed tiger and many other species characteristic of the ice age. It has often inferred that the demise of the “stone-age” mammals was due to the hunting practices of the stone-age peoples. However, some recent findings suggest the grim possibility of a nuclear winter leading to the animals’ demise.

Fig. 1 Mountain Avens, Dryas octopetala, Svalbard, July 2004, by Michael Haferkamp via Wikipedia

It should be emphasized that a Stone Age Nuclear Winter implies a meteor or comet impact (with the slight possibility of extreme volcanism). The concepts of Nuclear Winter and extinction events came to light in the 1980s with publications from primarily two different groups of researchers. The two concepts overlap in ways that do not appear similar to a casual observer—however, upon close examination both phenomena are similar in the following manner:

  • After device explosion or comet (or meteor) impact, firestorms ensue
  • Dust and smoke resulting from firestorms darken the sky—effectively blocking sunlight
  • Winter-type weather results from dust and smoke clouds
  • Animals and other life dependent on vegetation perish from lack of sunlight
  • Carnivorous animals perish as food chain collapses

At this point, however, let’s address the purported impact of a comet or asteroid during the latter stages of the Ice Age. The initial publication came in 2007 by Firestone et al in The Proceedings of the National Academy of Sciences—where the authors reported finding evidence that was indicative of either a comet or asteroid impaction in the Americas. The result of the impact led to a 1000 year period of unusual cooling for that period of de-glaciation. Since the initial publication of 5 ½ years ago, there have been numerous counter-publications addressing the findings of Firestone et al. The most glaring counter-claims indicate that Firestone et al simply did not know what they spoke-of. Many of the initially reported findings could not be re-produced. Needless to say, the work of Firestone et al falls under the rubric of challenging mainstream science. The methodology of Firestone and co-authors comes into question (for me) because there are no “hard numbers” to pin down their findings. (From a chemist’s view point, if one can give hard evidence in quantitative form—then half the battle is normally won.) Unfortunately, there is a certain amount of qualitative description in the reported findings—so until Firestone et al can devise a hard, analytical technique—the authors face an uphill battle for legitimacy.

In January of 2012, Firestone and fifteen other authors addressed his critics in The Proceedings of the National Academy of Sciences with a “better” study—although still qualitative in many respects. The group found evidence for impaction in the sedimentary layers at Lake Cuitzeo in Central Mexico. Although it is argued that studying sedimentary layers of a lake present many difficulties—the possibilities of examining a potentially undisturbed layer may bolster their case for impaction.

Here is the gist of their findings:

  • Deep layer of organic carbon—containing nano-diamonds, and other unusual microspheres that date to approximately 12.9 thousand years ago were uncovered and accurately dated

This layer of organic carbon is characteristic of their sites of previous investigation—it is that finding that their critics found hard to re-produce or accept. A significant detail that Firestone and co-workers have found to aid their work is the amount of carbon sediment. In their 2007 publication, their critics contended that Firestone et al did not see enough of any characteristic carbon. By uncovering the deep layer of black carbon, Firestone and co-workers re-opened the discussion.

In the publication of 2012, Firestone and co-workers have offered a working theory for why there seem to be inconsistencies between reporting researchers: the impacting comet/meteor must have been large enough to break apart and cause multiple impact sites. Upon further inspection, the lack of “impact craters” leads the workers to hypothesize that the event was similar to the Tunguska event—only upon a grander scale.

Since the 2012 publication, I turned up one counter-claim from a group of researchers in Australia. Not surprisingly, they could not confirm the results of Firestone outright.

In short:

  • There is a standing debate: did a large Tunguska-type event happen at the end of the last Ice Age
  • There is no hard, quantitative evidence for either side—(IMO) until one side can present a strong, quantitative argument there will be no clear resolution


For a fairly exhaustive (but dated) finding of the Younger Dryas Event (From Scientific American):

References used in post:

  • Alvarez, L W. 1983. “Experimental Evidence That an Asteroid Impact Led to the Extinction of Many Species 65 Million Years Ago.” Proceedings of the National Academy of Sciences of the United States of America 80 (2) (January): 627–42.
  • Condron, Alan, and Peter Winsor. 2012. “Meltwater Routing and the Younger Dryas.” Proceedings of the National Academy of Sciencesof the United States of America 109 (49) (December 4): 19928–33. doi:10.1073/pnas.1207381109.
  • Green, Helen, Jon Woodhead, John Hellstrom, Robyn Pickering, and Russell Drysdale. 2013. “Re-analysis of Key Evidence in the Case for a Hemispherically Synchronous Response to the Younger Dryas Climatic Event.” Journal of Quaternary Science 28 (1) (January 25): 216–216. doi:10.1002/jqs.2621.
  • Israde-alcántara, Isabel, James L Bischoff, Gabriela Domínguez-vázquez, Hong-chun Li, Paul S Decarli, Chris Mercer, Sujing Xie, Eric K Richman, Charles R Kinzie, and Wendy S Wolbach. 2012. “Evidence from Central Mexico Supporting the Younger Dryas Extraterrestrial Impact Hypothesis” 109 (13). doi:10.1073/pnas.1110614109/
  • Surovell, Todd a, Vance T Holliday, Joseph a M Gingerich, Caroline Ketron, C Vance Haynes, Ilene Hilman, Daniel P Wagner, Eileen Johnson, and Philippe Claeys. 2009. “An Independent Evaluation of the Younger Dryas Extraterrestrial Impact Hypothesis.” Proceedings of the National Academy of Sciences of the United States of America 106 (43) (October 27): 18155–8. doi:10.1073/pnas.0907857106.
  • Teller, James T. 2012. “Importance of Freshwater Injections into the Arctic Ocean in Triggering the Younger Dryas Cooling.” Proceedings of the National Academy of Sciences of the United States of America 109 (49) (December 4): 19880–1. doi:10.1073/pnas.1218344109.
  • Turco, Richard P., O. B. Toon, T. P. Ackerman, J. B. Pollack and C. Sagan. 1983. “Nuclear winter: Global consequences of multiple nuclear explosions,” Science, 222, 1283-1292 (1983).


2 thoughts on “Comet Impact in the Pleistocene Era Led to an Abrupt Climate Change?

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