Text #9335"Younger Dryas Impact Hypothesis", in .
The Younger Dryas impact hypothesis, also known as the Clovis comet hypothesis, is one of the competing scientific explanations for the onset of the Younger Dryas cold period after the last glacial period. The hypothesis, which scientists continue to debate, proposes that the climate of that time was cooled by the impact or air burst of one or more comets.
The general hypothesis states that about 12,900 BP calibrated (10,900 14C uncalibrated) years ago, air burst(s) or impact(s) from a near-Earth object(s) set areas of the North American continent on fire, disrupted climate and caused the Quaternary extinction event in North America. This resulted in the extinction of most of the megafauna, and the rapid demise of the North American Clovis culture. The Younger Dryas ice age lasted for about 1,200 years before the climate warmed again. These events are also seen as part of the Holocene extinction phenomenon.
One or more big explosions may have occurred above or possibly on the Laurentide Ice Sheet in the region of the Great Lakes. Though no major impact crater has been identified, the proponents suggest that it would be physically possible for such an air burst to have been similar to but orders of magnitude larger than the Tunguska event of 1908. The hypothesis proposed that animal and human life in North America not directly killed by the blast or the resulting wildfires would have suffered due to the disrupted ecologic relationships affecting the continent.
The impact of this postulated event (or series of events) goes beyond the Americas. A number of studies document this impact around the world. For example, James Wittke et al. document deposition of impact spherules 12,800 years ago across four continents, including Europe and the Middle East.
The evidence claimed for an impact event includes carbon-rich layers of soil that have been found at some 50 Clovis sites across the continent. The proponents report that layers contain unusual materials (nanodiamonds, metallic microspherules, carbon spherules, magnetic spherules, iridium, charcoal, soot, and fullerenes enriched in helium-3) that they interpret as evidence of an impact event, at the very bottom of black mats of organic material that they say marks the beginning of the Younger Dryas, and claim that this cannot be explained by volcanic, anthropogenic, and other natural processes.
Recent research has been reported that at Lake Cuitzeo, in the central Mexican state of Guanajuato, there is evidence supporting a modified version of the Younger Dryas impact hypothesis – involving a much smaller, non-cometary impactor – was found in lake bed cores dating to 12,900 BP. The reported evidence included nanodiamonds (including the hexagonal form called lonsdaleite), carbon spherules, and magnetic spherules. Multiple hypotheses were examined to account for these observations, though none were believed to be terrestrial. Lonsdaleite occurs naturally in asteroids and cosmic dust and as a result of extraterrestrial impacts on Earth. The analysis of the study has not been confirmed or repeated by other researchers.
A 100-fold spike in the concentration of platinum has also been found in Greenland ice cores, dated to 12,890 BP with 5 year accuracy. The source of the platinum has not yet been identified, but the researchers ruled out either earth’s mantle or stony meteorites (chondrites). The researchers said the source could be from an iron-rich impactor that probably would have left a crater of “few kilometers” in diameter, but none has so far been identified.
It is conjectured that this impact event brought about the extinction of many North American Pleistocene megafauna. These animals included camels, mammoths, the giant short-faced bear and numerous other species that the proponents suggest died at this time. The proposed markers for the impact event are claimed to appear at the end of the Clovis culture. However, some large animals survived that time period.
The genesis of this hypothesis goes back to the 1950s. In his work on the Lehner Mammoth-Kill Site near Hereford, Arizona, Emil Haury found Clovis point artifacts buried by a distinctive black clay layer. It was then known as “Lehner swamp soil”. This black soil was associated with a subhumid climate and ponding.
Later, Vance Haynes studied this phenomenon, and renamed it ‘black mat layer’. Over 60 geoarchaeological sites bridging the Pleistocene-Holocene transition (last deglaciation) exhibit this ‘black mat’; it is a black organic-rich layer in the form of mollic paleosols, aquolls, and diatomites. This layer typically covers the surfaces on which the last remnants of the terminal Pleistocene megafauna are recorded.
The full description and extension of this hypothesis was published in a 2006 book. The following year, a paper with the same principal authors suggested that the impact event may have led to an immediate decline in human populations in North America at that time.
Additional data purported to support the synchronous nature of the black mats was published. The author stated that the data required further analysis, and independent analysis of other Clovis sites for verification of this evidence. Vance Haynes (not to be confused with Prof. Gary Haynes, who also works in this area) stated that he remained skeptical of the bolide impact hypothesis as the cause of the Younger Dryas and the megafaunal extinction, concluding that “However (…) something major happened at 10,900 B.P. (14C uncalibrated) that we have yet to understand.”
Transmission electron microscopy evidence purported to show nanodiamonds from a layer assumed to correspond to the geologic moment of the event was published in the journal Science. Also, in the same issue, D.J. Kennett reported that the nano-diamonds were evidence for bolide impacts from a rare swarm of carbonaceous chondrites or comets at the start of Younger Dryas, resulting from multiple airbursts and surface impacts. This resulted in substantial loss of plant life, megafauna, and other animals. This study has been strenuously disputed by mainstream scientists for a variety of technical and professional reasons. Scientific skepticism increased with the revelation of documentation demonstrating misconduct and past criminal conduct (conviction for fraud and misrepresentation of credentials) by the researcher who prepared samples for the proponents of the hypothesis.
The disputing scientists claim that the study’s conclusions could not be repeated, that further research suggests that no nanodiamonds were found, and that the supposed carbon spherules were, in fact, either fungus or insect feces and included modern contaminants.
A re-evaluation published by the original proponents in June 2013 of spherules from 18 sites worldwide is seen by them as supporting their hypothesis.
In 2014, Kinzie, and an international collaboration of scientists published in The Journal of Geology research arguing that they had found what they interpreted to be “a thin layer over three continents, particularly in North America and Western Europe, that contain a rich assemblage of nanodiamonds, the production of which can be explained only by cosmic impact.”
Firestone, Richard; West, Allen; Warwick-Smith, Simon (4 June 2006). The Cycle of Cosmic Catastrophes: How a Stone-Age Comet Changed the Course of World Culture. Bear & Company.
Firestone RB, West A, Kennett JP, et al. (October 2007). “Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling”. Proc. Natl. Acad. Sci. U.S.A. 104 (41): 16016–21.
Bunch TE, Hermes RE, Moore AM, et al. (June 2012). “Very high-temperature impact melt products as evidence for cosmic airbursts and impacts 12,900 years ago”. Proc Natl Acad Sci U S A 109 (28): E1903–12.
Kennett DJ, Kennett JP, West A, et al. (January 2009). “Nanodiamonds in the Younger Dryas boundary sediment layer”. Science 323 (5910): 94.
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Wittke, James H.; Weaver, James C.; Bunch, Ted E.; Kennett, James P.; Kennett, Douglas J.; Moore, Andrew M. T.; Hillman, Gordon C.; Tankersley, Kenneth B.; Goodyear, Albert C.; Moore, Christopher R.; Daniel, I. Randolph; Ray, Jack H.; Lopinot, Neal H.; Ferraro, David; Israde-Alcántara, Isabel; Bischoff, James L.; Decarli, Paul S.; Hermes, Robert E.; Kloosterman, Johan B.; Revay, Zsolt; Howard, George A.; Kimbel, David R.; Kletetschka, Gunther; Nabelek, Ladislav; Lipo, Carl P.; Sakai, Sachiko; West, Allen; Firestone, Richard B. (2013). “Evidence for deposition of 10 million tonnes of impact spherules across four continents 12,800 y ago”. Proceedings of the National Academy of Sciences 110 (23): E2088.
Israde-Alcántara I, Bischoff JL, Domínguez-Vázquez G, et al. (March 2012). “Evidence from central Mexico supporting the Younger Dryas extraterrestrial impact hypothesis”. Proc. Natl. Acad. Sci. U.S.A. 109 (13): E738–47.
Michail I. Petaev, Shichun Huang, Stein B. Jacobsen, Alan Zindler (2013). “Large Pt anomaly in the Greenland ice core points to a cataclysm at the onset of Younger Dryas”. Proc. Natl. Acad. Sci. U.S.A. 110 (32): 12917–12920.
Haynes, G (5 November 2010). “The catastrophic extinction of North American mammoths and mastodonts”. World Archaeology 33 (3): 391–416.