[close] Younger Dryas event From Wikipedia, the free encyclopedia Jump to: navigation <#mw-head>, search <#p-search> The *Younger Dryas impact event* or *Clovis comet hypothesis* was the hypothesized large air burst or earth impact of an object or objects from outer space that initiated the Younger Dryas cold period about 12,900 BP calibrated (10,900 BP uncalibrated). One scenario proposes that an air burst and/or earth impact with a rare swarm of carbonaceous chondrites or comets set vast areas of the North American continent on fire, causing the extinction of most of the large animals in North America and the demise of the North American Clovis culture at the end of the last glacial period .^[1] <#cite_note-Kennett-0> This swarm would have exploded above or even into the Laurentide Ice Sheet north of the Great Lakes . An airburst would have been similar to but many orders of magnitude larger than the Tunguska event of 1908. Animal and human life not directly killed by the blast or the resulting coast to coast wildfires would have starved on the burned surface of the continent. The scenario is the product of a team of geologists at American universities, among them James Kennett of the University of California Santa Barbara , Richard Firestone of Lawrence Berkeley National Laboratory , as well as archaeologists Douglas Kennett ^[1] <#cite_note-Kennett-0> and Jon Erlandson of the University of Oregon . Forest destroyed by the similar Tunguska airburst event The scenario has been the subject of criticism and doubts. Impact specialists have studied the claim and concluded in 2010 that there never was such an impact, in particular because various physical signs of such an impact cannot be found.^[2] <#cite_note-1> Contents [hide <#>] * 1 Evidence <#Evidence> * 2 Results <#Results> * 3 History of the hypothesis <#History_of_the_hypothesis> * 4 Criticisms of the hypothesis <#Criticisms_of_the_hypothesis> * 5 See also <#See_also> * 6 References <#References> * 7 External reading <#External_reading> * 8 External links <#External_links> [edit ] Evidence The evidence claimed for an impact event includes a charred carbon-rich layer of soil that has been found at some 50 Clovis-age sites across the continent. The layer contains unusual materials (nanodiamonds , metallic microspherules , carbon spherules, magnetic spherules , iridium , charcoal, soot, and fullerenes enriched in helium-3 ) interpreted as evidence of an impact event, at the very bottom of the "black mat" of organic material that marks the beginning of the Younger Dryas.^[3] <#cite_note-Dalton-2> [edit ] Results It is conjectured that this impact event brought about the extinction of many North American large mammals. These animals included camels , mammoths , the giant short-faced bear and numerous other species. The markers for the impact event also appear at the end of the Clovis culture .^[4] <#cite_note-AGU2007JA-3> [edit ] History of the hypothesis The British science journal /Nature/ addressed the theory in a news story on 17 May 2007.^[5] <#cite_note-4> On 24 May 2007, a session at the spring 2007 joint assembly of the American Geophysical Union in Acapulco, Mexico was held to discuss this hypothesis and reveal the evidence.^[4] <#cite_note-AGU2007JA-3> On 27 September 2007, a paper presenting the findings of the Acapulco group was pre-published online at the Proceedings of the National Academy of Sciences website. According to the study, the impact event may have led to an immediate decline in human populations in North America at that time.^[6] <#cite_note-PNAS07A-5> Less than a year later substantial support for the synchronous nature of the black mat was provided by leading Clovis archaeologist, C. Vance Haynes , also in the PNAS . Says Haynes: Further analysis is in progress and other Clovis sites need independent study and verification of this evidence. Until then I remain skeptical of the ET impact hypothesis as the cause of the YD onset and the megafaunal extinction. However, I reiterate, something major happened at 10,900 B.P. that we have yet to understand.^[7] <#cite_note-6> The hypothesis drew new scrutiny in March 2008 at the annual meeting of the Society for American Archaeology in Vancouver, Canada. In August 2008, at the annual Pecos Archaeological Conference , Allen West , a lead proponent of the Clovis Comet hypothesis, and Ted Bunch , a co-author of the original PNAS paper and former NASA chief of exobiology, presented new evidence, and participated in a panel discussion of the findings with Sandia Labs asteroid impact modeler Mark Boslough , and comet hunter Carolyn Shoemaker .^[8] <#cite_note-7> Independent verification of Firestone and West's identification of extraterrestrial material in Clovis stratigraphy was presented by Mustafa Fayek and Sharon Hull of the University of Manitoba .^[9] <#cite_note-8> Most recently, In January 2009, transmission electron microscopy evidence showing nanodiamonds from the geologic moment of the event was published in the journal /Science/^[10] <#cite_note-Kerr-9> and reviewed in the International Herald Tribune.^[11] <#cite_note-Chang-10> Also, in the same issue, D.J. Kennett reported that: These diamonds provide strong evidence for Earth's collision with a rare swarm of carbonaceous chondrites or comets at the onset of the Younger Dryas cool interval, producing multiple airbursts and possible surface impacts, with severe repercussions for plants, animals, and humans in North America.^[1] <#cite_note-Kennett-0> [edit ] Criticisms of the hypothesis A study of Paleoindian demography published in August 2008 (almost a year after the first publication in PNAS) states "The results of the analyses were not consistent with the predictions of extraterrestrial impact hypothesis. No evidence of a population decline among the Paleoindians at 12,900 ± 100 calBP was found. Thus, minimally, the study suggests the extraterrestrial impact hypothesis should be amended." ^[12] <#cite_note-11> ^[13] <#cite_note-12> Nor is there evidence of continent-wide wildfires at any time during terminal Pleistocene deglaciation,^[14] <#cite_note-Marlonetal2009-13> which calls into question the origin of the "black mat". Iridium, magnetic minerals, microspherules, carbon, and nanodiamonds are all subject to differing interpretations as to their nature and origin, and may be explained in many cases by purely terrestrial and/or non-catastrophic factors.^[15] <#cite_note-PinterandIshman2008-14> Since it is assumed the effects of the putative impact on Earth's biota would have been brief, all extinctions caused by the impact should have occurred simultaneously. However, there is much evidence that the megafaunal extinctions that occurred across northern Eurasia, North America and South America at the end of the Pleistocene were not synchronous. The extinctions in South America appear to have occurred at least 400 years after the extinctions in North America.^[16] <#cite_note-Haynes-15> ^[17] <#cite_note-Fiedel-16> ^[18] <#cite_note-Fiedel2-17> The extinction of woolly mammoths in Siberia also appears to have occurred later than in North America.^[16] <#cite_note-Haynes-15> A greater disparity in extinction timings is apparent in island megafaunal extinctions that lagged nearby continental extinctions by thousands of years; examples include the survival of woolly mammoths on Wrangel Island , Russia , until 3700 BP,^[16] <#cite_note-Haynes-15> ^[17] <#cite_note-Fiedel-16> and the survival of ground sloths in the Antilles , the Caribbean , until 4700 cal BP.^[16] <#cite_note-Haynes-15> ^[17] <#cite_note-Fiedel-16> ^[18] <#cite_note-Fiedel2-17> The megafaunal extinction pattern observed in North America poses a problem for the bolide impact scenario, since it raises the question why large mammals should be preferentially exterminated over small mammals or other vertebrates.^[19] <#cite_note-Scott2010-18> Additionally, some extant megafaunal species such as bison and grizzlies seem to have been little affected by the extinction event, while the environmental devastation caused by a bolide impact would not be expected to discriminate.^[16] <#cite_note-Haynes-15> Skeptics of the theory have asserted that the carbon spherules originated as fungal structures and/or insect fecal pellets,^[20] <#cite_note-spherules-19> and that the claimed nanodiamonds are actually misidentified graphene and graphene/graphane oxide aggregates.^[21] <#cite_note-Daulton-20> ^[22] <#cite_note-Kerr2-21> [edit ] See also * Pleistocene megafauna * Holocene extinction event [edit ] References 1. ^ ^/*a*/ <#cite_ref-Kennett_0-0> ^/*b*/ <#cite_ref-Kennett_0-1> ^/*c*/ <#cite_ref-Kennett_0-2> Kennett,, D. J. Kennett; J. P. Kennett, A. West, C. Mercer, S. S.Que Hee, L. Bement, T. E. Bunch, M. Sellers, W. S. Wolbach (2009-1). "Nanodiamonds in the Younger Dryas Boundary Sediment Layer" . /Science/ (American Association for the Advancement of Science) *323.* (5910): 94. doi :10.1126/science.1162819 . ISSN 0036-8075 . PMID 19119227 . http://www.sciencemag.org/cgi/content/abstract/sci;323/5910/94. 2. *^ <#cite_ref-1>* Richard A. Kerr (3 September 2010). "Mammoth-Killer Impact Flunks Out". /Science/ *329* (5996): 1140–1. doi :10.1126/science.329.5996.1140 . PMID 20813931 . 3. *^ <#cite_ref-Dalton_2-0>* Dalton, Rex (2007-05-17). "Archaeology: Blast in the past?". /Nature/ *447* (7142): 256–257. doi :10.1038/447256a . PMID 17507957 . News article in /Nature / 4. ^ ^/*a*/ <#cite_ref-AGU2007JA_3-0> ^/*b*/ <#cite_ref-AGU2007JA_3-1> "Session Information, 2007 Joint Assembly, Paleoceanography and Paleoclimatology" . American Geophysical Union. http://www.agu.org/cgi-bin/sessions5?meeting=sm07&part=PP41A&maxhits=400. Retrieved 2007-05-22. Includes links to abstracts. 5. *^ <#cite_ref-4>* "Blast from the Past? A controversial new idea suggests that a big space rock exploded on or above North America at the end of the last ice age," by Rex Dalton, /Nature/, vol. 447, no. 7142, pages 256–257 (17 May 2007). Available on-line at: http://www.geo.arizona.edu/~reiners/blackmat.pdf 6. *^ <#cite_ref-PNAS07A_5-0>* "Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling" . The National Academy of Sciences. http://www.pnas.org/cgi/content/abstract/0706977104v1. Retrieved 2007-09-30. 7. *^ <#cite_ref-6>* Younger Dryas “black mats” and the Rancholabrean termination in North America, C. Vance Haynes, Jr., PNAS May 6, 2008 vol. 105 no. 18 6520-6525 8. *^ <#cite_ref-7>* Video of the August, 2008, Pecos Conference presentations on the Clovis Comet 9. *^ <#cite_ref-8>* Fayek and Hull, Pecos Archaeological Conference, Flagstaff, Arizona, August 10, 2008 10. *^ <#cite_ref-Kerr_9-0>* Kerr, Richard A. (2009-1). "Did the Mammoth Slayer Leave a Diamond Calling Card?" . /Science / (American Association for the Advancement of Science ) *323.* (5910,): 26. doi :10.1126/science.323.5910.26 . ISSN 0036-8075 . http://www.sciencemag.org/cgi/content/summary/323/5910/26. 11. *^ <#cite_ref-Chang_10-0>* Chang, Kenneth (2009-01-02). "Diamonds linked to quick cooling eons ago" . /Health and Science, International Herald Tribune/ (International Herald Tribune ). http://www.iht.com/articles/2009/01/02/healthscience/02impact.php. Retrieved 2009-01-03. 12. *^ <#cite_ref-11>* B Buchanan, M Collard & K Edinborough 2008. "Paleoindian demography and the extraterrestrial impact hypothesis " /PNAS/ August 19, 2008 vol. 105 no. 33 11651-11654 doi: 10.1073/pnas.0803762105 [1] 13. *^ <#cite_ref-12>* [2] 14. *^ <#cite_ref-Marlonetal2009_13-0>* J.R. Marlon et al. (2009) Wildfire responses to abrupt climate change in North America, Proceedings of the National Academy of Sciences 106 (8), 2519–2524 15. *^ <#cite_ref-PinterandIshman2008_14-0>* N. Pinter, S.E Ishman (2008) Impacts, mega-tsunami, and other extraordinary claims, GSA Today 18 (1), 37–38. 16. ^ ^/*a*/ <#cite_ref-Haynes_15-0> ^/*b*/ <#cite_ref-Haynes_15-1> ^/*c*/ <#cite_ref-Haynes_15-2> ^/*d*/ <#cite_ref-Haynes_15-3> ^/*e*/ <#cite_ref-Haynes_15-4> Haynes, Gary (2009). "Introduction to the Volume" . In Haynes, Gary. /American Megafaunal Extinctions at the End of the Pleistocene/ . Springer . pp. 1–20. doi :10.1007/978-1-4020-8793-6_1 . ISBN 978-1-4020-8792-9 . http://www.springerlink.com/content/w314m76738r91g35/?p=5af1eb7387d443a2b514b284c646efa7&pi=0 17. ^ ^/*a*/ <#cite_ref-Fiedel_16-0> ^/*b*/ <#cite_ref-Fiedel_16-1> ^/*c*/ <#cite_ref-Fiedel_16-2> Fiedel, Stuart (2009). "Sudden Deaths: The Chronology of Terminal Pleistocene Megafaunal Extinction" . In Haynes, Gary. /American Megafaunal Extinctions at the End of the Pleistocene/ . Springer . pp. 21–37. doi :10.1007/978-1-4020-8793-6_2 . ISBN 978-1-4020-8792-9 . http://www.springerlink.com/content/l225628681672725/?p=5af1eb7387d443a2b514b284c646efa7&pi=1 18. ^ ^/*a*/ <#cite_ref-Fiedel2_17-0> ^/*b*/ <#cite_ref-Fiedel2_17-1> Vergano, Dan (2009-01-02). "Study links mammoth extinction, comets" . /USA Today.Com /. Gannett Company . http://www.usatoday.com/tech/science/2009-01-01-mammothimpact_N.htm. Retrieved 2009-05-10. 19. *^ <#cite_ref-Scott2010_18-0>* Scott, E. (2010). "Extinctions, scenarios, and assumptions: Changes in latest Pleistocene large herbivore abundance and distribution in western North America". /Quat. Int./ *217*: 225. doi :10.1016/j.quaint.2009.11.003 . 20. *^ <#cite_ref-spherules_19-0>* Roach, John (2010-06-22). "Fungi, Feces Show Comet Didn't Kill Ice Age Mammals?" . /National Geographic Daily News /. National Geographic Society . http://news.nationalgeographic.com/news/2010/06/100622-science-environment-wildfires-cooling-ice-age-extinctions/. Retrieved 2010-06-25. 21. *^ <#cite_ref-Daulton_20-0>* Daulton, T. L.; Pinter, N.; Scott, A. C. (2010-08-30). "No evidence of nanodiamonds in Younger–Dryas sediments to support an impact event". /PNAS / (National Academy of Sciences ) *107* (37): 16043–7. doi :10.1073/pnas.1003904107 . PMID 20805511 . 22. *^ <#cite_ref-Kerr2_21-0>* Kerr, Richard A. (2010-10-30). "Mammoth-Killer Impact Rejected" . /Science NOW /. AAAS . http://news.sciencemag.org/sciencenow/2010/08/mammoth-killer-impact-rejected.html. Retrieved 2010-08-31. [edit ] External reading * THE CLOVIS COMET Part I:Evidence for a Cosmic Collision 12,900 Years Ago In the Mammoth Trumpet, Volume 23 Number 1, by Allen West GeoScience Consulting and Albert Goodyear South Carolina Institute of Archaeology and Anthropology. Accessed August 2008 * Clovis Comet at Real Science blog. Accessed August 2008 * New Clovis-Age Comet Impact Theory Newswise 2008 * New Clovis-Age Comet Impact Theory SpaceDaily.com May 23, 2007. Accessed August 2008. * New Scientist - Heather Pringle Firestorm from space wiped out prehistoric Americans 26 May 2007 [edit ] External links * PDF of abstracts of Oral Presentations for the 2009 AGU Fall Meeting, December 16, 2009, session titled "Younger Dryas Boundary: Extraterrestrial Impact or Not * PDF of abstracts of Poster Presentations for the 2009 AGU Fall Meeting, December 16, 2009, session titled "Younger Dryas Boundary: Extraterrestrial Impact or Not * Video of the 2007 AGU Acapulco Joint Assembly, and the 2008 Pecos Archeological Conference, where the theory and the evidence were presented * Hayek and Hull present independent verification at the annual Pecos Conference * Video of the AGU Press Conference announcing the discovery * Hoffman, Carey (2008-07-02). "Exploding Asteroid Theory Strengthened by New Evidence Located in Ohio, Indiana" . University of Cincinnati. http://www.uc.edu/news/NR.asp?id=8625. Retrieved 2008-08-05. * BBC: Diamond clues to beasts' demise * Nova (TV series) episode on the impact and its ramifications. 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