Younger Dryas impact hypothesis#Mainstream explanation

The Comet research group (CRG), dedicated to investigating the YDIH, was established in 2016 by Allen West{{efn|Allen West (originally Allen Whitt until he changed his name legally in 2006) is described as having no formal academic affiliation and a degree from a Bible college which he wouldn't name.}} (and others).{{Cite web |last=Dalton |first=Rex |name-list-style=vanc |date=May 14, 2011 |title=Comet Theory Comes Crashing to Earth |url=https://psmag.com/environment/comet-claim-comes-crashing-to-earth-31180 |url-status=live |archive-url=https://web.archive.org/web/20210211004633/https://psmag.com/environment/comet-claim-comes-crashing-to-earth-31180 |archive-date=11 February 2021 |access-date=24 July 2019 |website=Pacific Standard}}{{Cite news |date=2024-03-05 |title=The Comet Strike Theory That Just Won’t Die |url=https://www.nytimes.com/2024/03/05/magazine/younger-dryas-impact-hypothesis-comet.html |archive-url=http://web.archive.org/web/20241213134927/https://www.nytimes.com/2024/03/05/magazine/younger-dryas-impact-hypothesis-comet.html |archive-date=2024-12-13 |access-date=2024-12-19 |language=en}} Their stated mission is to "find evidence about comet impacts and raise awareness about them before your city is next."{{Cite web |date=2015-07-14 |title=Comet Research Group |url=https://cometresearchgroup.org/ |access-date=2024-11-24 |website= |language=en-US}}

The credibility and motivations of individual CRG researchers have been questioned by critics of the impact hypothesis, including their specific claims for evidence in support of the YDIH and/or the effects of meteor air bursts or impact events on ancient settlements, people, and environments. Doubts have been raised about several of the CRG's other claims.;{{cite web |last=Marcus |first=Adam |date=1 October 2021 |title=Criticism engulfs paper claiming an asteroid destroyed Biblical Sodom and Gomorrah |url=https://retractionwatch.com/2021/10/01/criticism-engulfs-paper-claiming-an-asteroid-destroyed-biblical-sodom-and-gomorrah/ |access-date=24 November 2021 |website=Retraction Watch}} for example a 2021 paper suggested that a Tunguska-sized or larger airburst destroyed Tall el-Hammam, a Middle Bronze Age city located in the Jordan Valley near the Dead Sea around 1650 BCE.{{Cite journal |last1=Bunch |first1=Ted E. |last2=LeCompte |first2=Malcolm A. |last3=Adedeji |first3=A. Victor |last4=Wittke |first4=James H. |last5=Burleigh |first5=T. David |last6=Hermes |first6=Robert E. |last7=Mooney |first7=Charles |last8=Batchelor |first8=Dale |last9=Wolbach |first9=Wendy S. |last10=Kathan |first10=Joel |last11=Kletetschka |first11=Gunther |last12=Patterson |first12=Mark C. L. |last13=Swindel |first13=Edward C. |last14=Witwer |first14=Timothy |last15=Howard |first15=George A. |date=2021-09-20 |title=RETRACTED ARTICLE: A Tunguska sized airburst destroyed Tall el-Hammam a Middle Bronze Age city in the Jordan Valley near the Dead Sea |journal=Scientific Reports |language=en |volume=11 |issue=1 |pages=18632 |bibcode=2021NatSR..1118632B |doi=10.1038/s41598-021-97778-3 |issn=2045-2322 |pmc=8452666 |pmid=34545151}}{{Retracted|doi=10.1038/s41598-025-99265-5|pmid=40275027|https://retractionwatch.com/2025/04/23/sodom-comet-paper-to-be-retracted-two-years-after-editors-note-acknowledging-concerns/ Retraction Watch}} Image forensics expert Elisabeth Bik discovered evidence for digital alteration of images used as evidence for the claim that the village of Tall el-Hammam was engulfed by an airburst.{{Cite news |date=6 October 2021 |title=Paper That Claimed Asteroid Destroyed Biblical Sodom Comes Under Pall of Doubt |url=https://science.thewire.in/society/religion/tall-el-hammam-sodom-asteroid-destruction-image-manipulation/ |work=The Science Wire}}{{Cite web |last=Kincaid |first=Ellie |date=2023-02-21 |title=Journal investigating Sodom comet paper for data problems |url=https://retractionwatch.com/2023/02/21/journal-investigating-sodom-comet-paper-for-data-problems/ |access-date=2024-11-23 |website=Retraction Watch |language=en-US}} CRG members initially denied tampering with the photos but eventually published a correction in which they admitted to inappropriate image manipulation.{{Cite Q|Q111021706|author-link19=James P. Kennett|last1=Bunch|first1=Ted E.|last2=LeCompte|first2=Malcolm A.|last3=Adedeji|first3=A. Victor|last4=Wittke|first4=James H.|last5=Burleigh|first5=T. David|last6=Hermes|first6=Robert E.|last7=Mooney|first7=Charles|last8=Batchelor|first8=Dale|last9=Wolbach|first9=Wendy S.|last10=Kathan|first10=Joel|last11=Kletetschka|first11=Gunther|last12=Patterson|first12=Mark C. L.|last13=Swindel|first13=Edward C.|last14=Witwer|first14=Timothy|last15=Howard|first15=George A.|last16=Mitra|first16=Siddhartha|last17=Moore|first17=Christopher R.|last18=Langworthy|first18=Kurt|last19=Kennett|first19=James P.|last20=West|first20=Allen|last21=Silvia|first21=Phillip J.|display-authors=8|doi-access=free}} Five of the paper's 53 images received retouching to remove labels and arrows present in other published versions of the photos, which Bik believed to be a possible conflict with Scientific Reports' image submission guidelines but was not in itself a disproval of the Tall el-Hammam airburst theory.{{Cite web |last=Bik |first=Elisabeth |author-link=Elisabeth Bik |date=2 October 2021 |title=Blast in the Past: Image concerns in paper about comet that might have destroyed Tall el-Hammam |url=https://scienceintegritydigest.com/2021/10/01/blast-in-the-past-image-concerns-in-paper-about-comet-that-might-have-destroyed-tall-el-hammam/ |access-date=24 November 2021 |website=Science Integrity Digest}} Subsequent concerns that have been brought up in PubPeer have not yet been addressed by the CRG, including discrepancies between claimed blast wave direction compared to what the images show, unavailability of original image data to independent researchers, lack of supporting evidence for conclusions, inappropriate reliance on young Earth creationist literature, misinformation about the Tunguska explosion, and another uncorrected example of an inappropriately altered image.{{Cite journal |last1=Bunch |first1=Ted E. |last2=Lecompte |first2=Malcolm A. |last3=Adedeji |first3=A. Victor |last4=Wittke |first4=James H. |last5=Burleigh |first5=T. David |last6=Hermes |first6=Robert E. |last7=Mooney |first7=Charles |last8=Batchelor |first8=Dale |last9=Wolbach |first9=Wendy S. |last10=Kathan |first10=Joel |last11=Kletetschka |first11=Gunther |last12=Patterson |first12=Mark C. L. |last13=Swindel |first13=Edward C. |last14=Witwer |first14=Timothy |last15=Howard |first15=George A. |date=September 2021 |title=A Tunguska sized airburst destroyed Tall el-Hammam a Middle Bronze Age city in the Jordan Valley near the Dead Sea |url=https://pubpeer.com/publications/37B87CAC48DE4BC98AD40E00330143# |journal=Scientific Reports |volume=11 |issue=1 |page=18632 |doi=10.1038/s41598-021-97778-3 |pmc=8452666 |pmid=34545151 |access-date=9 August 2022 |last16=Mitra |first16=Siddhartha |last17=Moore |first17=Christopher R. |last18=Langworthy |first18=Kurt |last19=Kennett |first19=James P. |last20=West |first20=Allen |last21=Silvia |first21=Phillip J.|bibcode=2021NatSR..1118632B }}{{Retracted|doi=10.1038/s41598-025-99265-5|pmid=40275027|https://retractionwatch.com/2025/04/23/sodom-comet-paper-to-be-retracted-two-years-after-editors-note-acknowledging-concerns/ Retraction Watch}} On February 15, 2023, the following editor’s note was posted on this paper: "Readers are alerted that concerns raised about the data presented and the conclusions of this article are being considered by the Editors. A further editorial response will follow the resolution of these issues."{{cite web |last=Kincaid |first=Ellie |date=February 21, 2023 |title=Journal investigating Sodom comet paper for data problems |url=https://retractionwatch.com/2023/02/21/journal-investigating-sodom-comet-paper-for-data-problems// |access-date=February 27, 2023 |website=Retraction Watch}} On August 30, 2023, a paper authored by a CRG member and leading YDIH advocate was retracted by Scientific Reports. The journal's Retraction Note cited a publication "indicating that the study does not provide data to support the claims of an airburst event or that such an event led to the decline of the Hopewell culture."{{Cite journal |last1=Tankersley|first1=K.B. |last2=Meyers|first2=S.D. |last3=Meyers |first3=S.A. |last4=Jordan|first4=J.A. |last5=Herzner|first5=L. |last6=Lentz|first6=D.L. |last7=Zedaker|first7=D. |date=August 2023 |title=Retraction Note: The Hopewell airburst event, 1699–1567 years ago (252–383 CE) |journal=Scientific Reports |volume=13 |issue=1 |page=14201 |doi=10.1038/s41598-023-41237-8 |doi-access=free |pmid=37648734 |pmc=10468503 |bibcode=2023NatSR..1314201T }}

Proponents believe that certain microscopic debris is evidence of impact and that "black mats" of sediment are evidence of widespread fires. They contend that extinction of megafauna was synchronous with associated effects on prehistoric human societies. They say that their observations and interpretations cannot be adequately explained by volcanic, anthropogenic, or other natural processes. They argue that there is a synchronous Younger Dryas boundary layer that should be used as a local,{{Cite Q |Q106891675 |last=Andronikov |first=Alexandre V. |last2=Andronikova |first2=Irina E. |last3=Loehn |first3=Clayton W. |last4=Lafuente |first4=Barbara |last5=Ballenger |first5=Jesse A. M. |last6=Crawford |first6=George T. |last7=Lauretta |first7=Dante S. |author-link7=Dante Lauretta |name-list-style=vanc |quote=The presence of the high number of such microspherules in the sediments can serve as a local stratigraphic marker in identification of the [lower Younger Dryas boundary] there where dark variety of the black mat is absent.}} or even global{{Cite journal |author-link6=Albert Goodyear |author-link10=James P. Kennett |display-authors=8 |vauthors=Moore CR, West A, LeCompte MA, Brooks MJ, Daniel IR, Goodyear AC, Ferguson TA, Ivester AH, Feathers JK, Kennett JP, Tankersley KB, Adedeji AV, Bunch TE |date=March 2017 |title=Widespread platinum anomaly documented at the Younger Dryas onset in North American sedimentary sequences |journal=Scientific Reports |volume=7 |issue=1 |page=44031 |bibcode=2017NatSR...744031M |doi=10.1038/srep44031 |pmc=5343653 |pmid=28276513 |quote=We expect the Pt anomaly to serve as a widely-distributed time marker horizon (datum) for identification and correlation of the onset of the YD climatic episode at 12,800 Cal B.P. This Pt datum will facilitate the dating and correlating of archaeological, paleontological, and paleoenvironmental data between sequences, especially those with limited age control.}} stratigraphic marker. Archaeologist Stuart J Fiedel has remarked that "The bolide and its effects have been characterized inconsistently from one paper to the next, which makes this hypothesis difficult to refute."{{Cite journal |last=Fiedel |first=Stuart J |title=Initial Human Colonization of the Americas, Redux |date=August 2022 |url=https://www.cambridge.org/core/product/identifier/S003382222100103X/type/journal_article |journal=Radiocarbon |language=en |volume=64 |issue=4 |pages=845–897 |doi=10.1017/RDC.2021.103 |bibcode=2022Radcb..64..845F |s2cid=246024355 |issn=0033-8222}} In 2011, a review of the evidence led researchers to state "The YD impact hypothesis provides a cautionary tale for researchers, the scientific community, the press, and the broader public" as "none of the original YD impact signatures have been subsequently corroborated by independent tests. Of the 12 original lines of evidence, seven have so far proven to be non-reproducible. The remaining signatures instead seem to represent either (1) non-catastrophic mechanisms, and/or (2) terrestrial rather than extraterrestrial or impact-related sources. In all of these cases, sparse but ubiquitous materials seem to have been misreported and misinterpreted as singular peaks at the onset of the YD. Throughout the arc of this hypothesis, recognized and expected impact markers were not found, leading to proposed YD impactors and impact processes that were novel, self-contradictory, rapidly changing, and sometimes defying the laws of physics."{{Cite journal |last1=Pinter |first1=Nicholas |last2=Scott |first2=Andrew C. |last3=Daulton |first3=Tyrone L. |last4=Podoll |first4=Andrew |last5=Koeberl |first5=Christian |last6=Anderson |first6=R. Scott |last7=Ishman |first7=Scott E. |date=2011-06-01 |title=The Younger Dryas impact hypothesis: A requiem |url=https://www.sciencedirect.com/science/article/pii/S0012825211000262 |journal=Earth-Science Reviews |language=en |volume=106 |issue=3 |pages=247–264 |doi=10.1016/j.earscirev.2011.02.005 |bibcode=2011ESRv..106..247P |issn=0012-8252}} Additionally, a comprehensive refutation of the Younger Dryas Impact Hypothesis was published in 2023, stating "There is no support for the basic premise of the YDIH that human populations were diminished, and individual species of late Pleistocene megafauna became extinct or were diminished due to catastrophe."{{Rp|location=Sec 3.2}} Another example is that of extensive wildfires claimed by some YDIH proponents{{Cite journal |last1=Wolbach |first1=Wendy S. |last2=Ballard |first2=Joanne P. |last3=Mayewski |first3=Paul A. |last4=Adedeji |first4=Victor |last5=Bunch |first5=Ted E. |last6=Firestone |first6=Richard B. |last7=French |first7=Timothy A. |last8=Howard |first8=George A. |last9=Israde-Alcántara |first9=Isabel |last10=Johnson |first10=John R. |last11=Kimbel |first11=David |last12=Kinzie |first12=Charles R. |last13=Kurbatov |first13=Andrei |last14=Kletetschka |first14=Gunther |last15=LeCompte |first15=Malcolm A. |date=March 2018 |title=Extraordinary Biomass-Burning Episode and Impact Winter Triggered by the Younger Dryas Cosmic Impact ∼12,800 Years Ago. 1. Ice Cores and Glaciers |url=https://www.journals.uchicago.edu/doi/10.1086/695703 |journal=The Journal of Geology |language=en |volume=126 |issue=2 |pages=165–184 |doi=10.1086/695703 |bibcode=2018JG....126..165W |s2cid=53021110 |issn=0022-1376}} that has been refuted by experts.{{Cite news |last=Gramling |first=Carolyn |name-list-style=vanc |date=2018-06-26 |title=Why won't this debate about an ancient cold snap die? |url=https://www.sciencenews.org/article/younger-dryas-comet-impact-cold-snap |url-status=live |archive-url=https://web.archive.org/web/20210805112551/https://www.sciencenews.org/article/younger-dryas-comet-impact-cold-snap |archive-date=2021-08-05 |access-date=2023-02-23 |work=Science News |language=en-US}}{{Rp|location=Sec. 9}}  "Evidence and arguments purported to support the YDIH involve flawed methodologies, inappropriate assumptions, questionable conclusions, misstatements of fact, misleading information, unsupported claims, irreproducible observations, logical fallacies, and selected omission of contrary information."

Proponents have reported materials including nanodiamonds, metallic microspherules, carbon spherules, magnetic spherules, iridium, platinum, platinum/palladium ratios, charcoal, soot, and fullerenes enriched with helium-3 that they interpret as evidence for an impact event that marks the beginning of the Younger Dryas.{{Cite journal |author-link4=James P. Kennett |author-link6=Andrew M. T. Moore |author-link7=Gordon Hillman |author-link9=Albert Goodyear |display-authors=8 |vauthors=Wittke JH, Weaver JC, Bunch TE, Kennett JP, Kennett DJ, Moore AM, Hillman GC, Tankersley KB, Goodyear AC, Moore CR, Daniel IR, Ray JH, Lopinot NH, Ferraro D, Israde-Alcántara I, Bischoff JL, DeCarli PS, Hermes RE, Kloosterman JB, Revay Z, Howard GA, Kimbel DR, Kletetschka G, Nabelek L, Lipo CP, Sakai S, West A, Firestone RB |date=June 2013 |title=Evidence for deposition of 10 million tonnes of impact spherules across four continents 12,800 y ago |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=110 |issue=23 |pages=E2088–97 |bibcode=2013PNAS..110E2088W |doi=10.1073/pnas.1301760110 |pmc=3677428 |pmid=23690611 |doi-access=free}} One of the most widely publicized discoveries (nanodiamonds in Greenland) has never been verified and is disputed.{{cite web |last1=Kurbatov |first1=Andrei V. |last2=Mayewski |first2=Paul A. |last3=Steffensen |first3=Jorgen P. |last4=West |first4=Allen |last5=Kennett |first5=Douglas J. |last6=Kennett |first6=James P. |last7=Bunch |first7=Ted E. |last8=Handley |first8=Mike |last9=Introne |first9=Douglas S. |date=2022-09-20 |title=Discovery of a nanodiamond-rich layer in the Greenland ice sheet |url=https://pubpeer.com/publications/28B83ADB820618B3F374667D5FBB92 |access-date=2022-09-28 |website=PubPeer |last10=Hee |first10=Shane S. Que |last11=Mercer |first11=Christopher |last12=Sellers |first12=Marilee |last13=Shen |first13=Feng |last14=Sneed |first14=Sharon B. |last15=Weaver |first15=James C. |last16=Wittke |first16=James H. |last17=Stafford |first17=Thomas W. |last18=Donovan |first18=John J. |last19=Xie |first19=Sujing |last20=Razink |first20=Joshua J. |last21=Stich |first21=Adrienne |last22=Kinzie |first22=Charles R. |last23=Wolbach |first23=Wendy S.}}

Some scientists have asserted that the carbon spherules originated as fungal structures and/or insect fecal pellets, and contained modern contaminants{{Cite web |last=Roach |first=John |name-list-style=vanc |date=22 June 2010 |title=Fungi, Feces Show Comet Didn't Kill Ice Age Mammals? |url=https://www.nationalgeographic.com/science/article/100622-science-environment-wildfires-cooling-ice-age-extinctions |url-access=limited |url-status=dead |archive-url=https://web.archive.org/web/20210717200455/https://www.nationalgeographic.com/science/article/100622-science-environment-wildfires-cooling-ice-age-extinctions |archive-date=17 July 2021 |access-date=17 July 2021 |website=National Geographic}} and that the claimed nanodiamonds are actually misidentified graphene and graphene/graphane oxide aggregates.{{Cite journal |author-link3=Andrew Cunningham Scott |vauthors=Daulton TL, Pinter N, Scott AC |date=September 2010 |title=No evidence of nanodiamonds in Younger-Dryas sediments to support an impact event |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=107 |issue=37 |pages=16043–7 |bibcode=2010PNAS..10716043D |doi=10.1073/pnas.1003904107 |pmc=2941276 |pmid=20805511 |doi-access=free}}{{Cite web |last=Kerr |first=Richard A. |author-link=Richard Kerr (science journalist) |name-list-style=vanc |date=30 October 2010 |title=Mammoth-Killer Impact Rejected |url=https://www.science.org/content/article/mammoth-killer-impact-rejected |url-status=live |archive-url=https://web.archive.org/web/20180917181633/http://www.sciencemag.org/news/2010/08/mammoth-killer-impact-rejected |archive-date=17 September 2018 |access-date=17 September 2018 |website=Science NOW |publisher=AAAS}} A patent application by Allen West and James Kennett in 2009 for methods of forming nanodiamonds based on research in support of the impact hypothesis also likely misidentified copper and copper oxides and appears to have since been abandoned.{{Rp|location=Sec. 12.5}} 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 or non-catastrophic factors.{{Cite journal |vauthors=Pinter N, Ishman SE |year=2008 |title=Impacts, mega-tsunami, and other extraordinary claims |journal=GSA Today |volume=18 |issue=1 |pages=37–38 |doi=10.1130/GSAT01801GW.1 |doi-access=free|bibcode=2008GSAT...18a..37P }}{{Cite web |date=23 April 2012 |title=No Love for Comet Wipeout |url=https://www.science.org/content/article/no-love-comet-wipeout |url-status=live |archive-url=https://web.archive.org/web/20180917181709/http://www.sciencemag.org/news/2012/04/no-love-comet-wipeout |archive-date=17 September 2018 |access-date=17 September 2018 |publisher=Science |vauthors=Perkins S}} An analysis of a similar Younger Dryas boundary layer in Belgium yielded carbon crystalline structures such as nanodiamonds, but the authors concluded that they did not show unique evidence for a bolide impact.{{Cite journal |vauthors=Tian H, Schryvers D, Claeys P |date=January 2011 |title=Nanodiamonds do not provide unique evidence for a Younger Dryas impact |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=108 |issue=1 |pages=40–4 |bibcode=2011PNAS..108...40T |doi=10.1073/pnas.1007695108 |pmc=3017148 |pmid=21173270 |doi-access=free}} An independent group of researchers reported much lower concentrations of platinum group metals in the purported boundary layer (by a factor of 30 for iridium).{{efn|One of the authors of this study, Matthew Boyd, later published a paper that argued in favour of the impact hypothesis.{{Cite Q |Q106863462 |last1=Teller |first1=James |last2=Boyd |first2=Matthew |last3=LeCompte |first3=Malcolm |last4=Kennett |first4=James P. |author-link4=James P. Kennett |last5=West |first5=Allen |last6=Telka |first6=Alice |last7=Diaz |first7=Aura |last8=Adedeji |first8=Victor |last9=Batchelor |first9=Dale |last10=Mooney |first10=Charles |last11=Garcia |first11=Roberto |display-authors=8 |name-list-style=vanc |quote=We propose that this massive hydrological reorganization resulted from a cosmic impact event at the YD boundary.}}}}{{Cite journal |author-link7=Vance T. Holliday |author-link8=Vance Haynes |display-authors=8 |vauthors=Paquay FS, Goderis S, Ravizza G, Vanhaeck F, Boyd M, Surovell TA, Holliday VT, Haynes CV, Claeys P |date=December 2009 |title=Absence of geochemical evidence for an impact event at the Bølling-Allerød/Younger Dryas transition |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=106 |issue=51 |pages=21505–10 |bibcode=2009PNAS..10621505P |doi=10.1073/pnas.0908874106 |pmc=2799824 |pmid=20007789 |doi-access=free}}{{Cite journal |vauthors=Paquay FS, Goderis S, Ravizza G, Claeys P |date=December 2009 |title=Reply to Bunch et al.: Younger Dryas impact proponents challenge new platinum group elements and osmium data unsupportive of their hypothesis |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=107 |issue=51 |pages=E59–E60 |doi=10.1073/pnas.1001828107 |doi-access=free|pmc=2872459 }} The original authors argued that these concentrations were still >300% (a factor of 3) above background in 2 of their samples.{{Cite journal |display-authors=8 |vauthors=Bunch, TE, West, A, Firestone, RB, Kennett, JP, Wittke, JH, Kinzie, CR, Wolbach, WS |date=April 2010 |title=Geochemical data reported by Paquay et al. do not refute Younger Dryas impact event |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=107 |issue=15 |pages=E58; author repliy E59-60 |doi=10.1073/pnas.1001156107 |pmid=20388907 |pmc=2872453 |bibcode=2010PNAS..107E..58B |doi-access=free}} Another group was unable to confirm prior claims of magnetic particles and microspherules in 2009.{{Cite journal |author-link2=Vance T. Holliday |author-link5=Vance Haynes |display-authors=8 |vauthors=Surovell TA, Holliday VT, Gingerich JA, Ketron C, Haynes CV, Hilman I, Wagner DP, Johnson E, Claeys P |date=October 2009 |title=An independent evaluation of the Younger Dryas extraterrestrial impact hypothesis |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=106 |issue=43 |pages=18155–8 |bibcode=2009PNAS..10618155S |doi=10.1073/pnas.0907857106 |pmc=2775309 |pmid=19822748 |doi-access=free}} Other studies involving YDIH proponents found concentrations of magnetic spherules but not all were associated with the YDB and not all were attributed to an ET event.{{Cite journal |display-authors=1 |vauthors=Haynes, CV |date=October 2010 |title=The Murray Springs Clovis site, Pleistocene extinction, and the question of extraterrestrial impact |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=107 |issue=9 |pages=4010–5 |doi=10.1073/pnas.0908191107 |pmid=20160115 |pmc=2840150 |bibcode=2010PNAS..107.4010H |doi-access=free}}{{Cite journal |display-authors=7 |vauthors=LeCompte MA, Goodyear AC, Demitroff MN, Batchelor D, Vogel EK, Mooney C, Rock BN, Siedel AW |date=October 2012 |title=Independent evaluation of conflicting microspherule results from different investigations of the Younger Dryas impact hypothesis |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=109 |issue=44 |pages=E2960-9 |doi=10.1073/pnas.1208603109 |pmid=22988071 |pmc=3497834 |doi-access=free}}{{cite journal |last1=Andronikov |first1=Alexandre V. |last2=Andronikova |first2=Irina E. |last3=Loehn |first3=Clayton W. |last4=Lafuente |first4=Barbara |last5=Ballenger |first5=Jesse A. M. |last6=Crawford |first6=George T. |last7=Lauretta |first7=Dante S. |author-link7=Dante Lauretta |date=2016 |title=Implications from chemical, structural and mineralogical studies of magnetic microspherules from around the lower younger dryas boundary (New Mexico, USA) |journal=Geografiska Annaler: Series A, Physical Geography |language=en |volume=98 |issue=1 |pages=39–59 |doi=10.1111/geoa.12122 |bibcode=2016GeAnA..98...39A |s2cid=56032364 |name-list-style=vanc}}{{Cite journal |display-authors=8 |vauthors=Kletetschka G, Vondrak D, Hruba J, Prochazka V, Nabelek L, Svitavska-Svoboda H, Bobek P, Horicka Z, Kadlec J, Takac M, Stuchlik E |date=October 2018 |title=Cosmic-impact event in lake sediments from central Europe postdates the Laacher See Eruption and marks onset of the Younger Dryas |journal=The Journal of Geology |volume=126 |issue=6 |pages=561–575 |doi=10.1086/699869 |bibcode=2018JG....126..561K |doi-access=free}}{{Cite journal |display-authors=8 |vauthors=Teller J, Boyd M, LeCompte MA, Kennett JP, West A, Telka A, Diaz A, Adedeji V, Batchelor D, Mooney C, Garcia R |date=October 2019 |title=A multi-proxy study of changing environmental conditions in a Younger Dryas sequence in southwestern Manitoba, Canada, and evidence for an extraterrestrial event |journal=Quaternary Research |volume=93 |pages=60–87 |doi=10.1017/qua.2019.46|s2cid=210614208 }}

The evidence given by proponents of a bolide or meteorite impact event includes "black mats", or strata of organic-rich soil that have been identified at about 50 archaeological sites across North America.{{efn|name=Black mat note|The darkened stratum was first identified at the Lehner Mammoth-Kill Site by Emil Haury who named it "Lehner swamp soil";{{Cite Q |Q59224169 |author-link1=Emil Haury |last=Haury |first=Emil W. |last2=Sayles |first2=E. B. |last3=Wasley |first3=William W. |name-list-style=vanc}} it was later renamed by Vance Haynes as the "black mat".{{Cite web |title= Paleoindian Studies and Geoarchaeology at the University of Arizona |url=http://www.argonaut.arizona.edu/history.htm |url-status=dead |archive-url=https://web.archive.org/web/20180723064120/http://www.argonaut.arizona.edu/history.htm |archive-date=2018-07-23 |website=University of Arizona |quote=Vance Haynes later renamed it the 'black mat'}}}} Using statistical analysis and modeling, James P. Kennett and others concluded that widely separated organic-rich layers, including black mats, were deposited synchronously across multiple continents as an identifiable Younger Dryas boundary layer.{{Cite Q|Q35718070|last1=Kennett|first1=James P|last2=Kennett|first2=Douglas J|last3=Culleton|first3=Brendan J|last4=Tortosa|first4=J Emili Aura|last5=Bischoff|first5=James L|last6=Bunch|first6=Ted E|last7=Daniel|first7=I Randolph|last8=Erlandson|first8=Jon M|last9=Ferraro|first9=David|last10=Firestone|first10=Richard B|last11=Goodyear|first11=Albert C|last12=Israde-Alcántara|first12=Isabel|last13=Johnson|first13=John R|last14=Pardo|first14=Jesús F Jordá|last15=Kimbel|first15=David R|last16=LeCompte|first16=Malcolm A|last17=Lopinot|first17=Neal H|last18=Mahaney|first18=William C|last19=Moore|first19=Andrew M T|last20=Moore|first20=Christopher R|last21=Ray|first21=Jack H|last22=Stafford|first22=Thomas W|last23=Tankersley|first23=Kenneth Barnett|last24=Wittke|first24=James H|last25=Wolbach|first25=Wendy S|last26=West|first26=Allen|author-link1=James P. Kennett|author-link8=Jon M. Erlandson|author-link11=Albert Goodyear|author-link19=Andrew M. T. Moore|display-authors=8|name-list-style=vanc}} In 2019, Jorgeson and others tested this conclusion with the simulation of radiocarbon ages.{{Cite journal |last1=Jorgeson |first1=Ian A. |last2=Breslawski |first2=Ryan P. |last3=Fisher |first3=Abigail E. |name-list-style=vanc |date=13 February 2020 |title=Radiocarbon simulation fails to support the temporal synchroneity requirement of the Younger Dryas impact hypothesis |url=https://www.cambridge.org/core/journals/quaternary-research/article/abs/radiocarbon-simulation-fails-to-support-the-temporal-synchroneity-requirement-of-the-younger-dryas-impact-hypothesis/6478BF9FD2E63B22C6152075E1B5C089 |url-status=live |journal=Quaternary Research |volume=96 |pages=123–139 |bibcode=2020QuRes..96..123J |doi=10.1017/qua.2019.83 |issn=1096-0287 |archive-url=https://web.archive.org/web/20210620182032/https://www.cambridge.org/core/journals/quaternary-research/article/abs/radiocarbon-simulation-fails-to-support-the-temporal-synchroneity-requirement-of-the-younger-dryas-impact-hypothesis/6478BF9FD2E63B22C6152075E1B5C089 |archive-date=20 June 2021 |s2cid=213657406}} They accounted for measurement error, calibration uncertainty, "old wood" effects, and laboratory measurement biases, and compared against the dataset of radiocarbon ages for the Laacher See eruption. They found the Laacher See 14C dataset to be consistent with expectations of synchroneity. They found the Younger Dryas boundary layer 14C dataset to be inconsistent with the expectations for its synchroneity, and the synchronous global deposition of the hypothesized Younger Dryas boundary layer to be extremely unlikely.

Marlon et al. suggest that wildfires were a consequence of rapid climate change.{{Cite journal |display-authors=8 |vauthors=Marlon JR, Bartlein PJ, Walsh MK, Harrison SP, Brown KJ, Edwards ME, Higuera PE, Power MJ, Anderson RS, Briles C, Brunelle A, Carcaillet C, Daniels M, Hu FS, Lavoie M, Long C, Minckley T, Richard PJ, Scott AC, Shafer DS, Tinner W, Umbanhowar CE, Whitlock C |date=February 2009 |title=Wildfire responses to abrupt climate change in North America |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=106 |issue=8 |pages=2519–24 |bibcode=2009PNAS..106.2519M |doi=10.1073/pnas.0808212106 |pmc=2650296 |pmid=19190185 |quote=...the charcoal data indicate an important role for climate, and particularly rapid climate change, in determining broad-scale levels of fire activity. |doi-access=free |author-link19=Andrew Cunningham Scott |author-link23=Cathy Whitlock}} "The changes in woody biomass, fire frequency, and biomass burning are not coincident with changes in CO2, although increasing CO2 may have contributed to woody biomass production during the early part of the Bølling–Allerød. Clovis people appeared in North America between 13.4 and 12.8 ka, broadly coincident with the sharp increase in biomass burning at 13.2 ka, and then rapidly spread out across the continent."

Radiocarbon dating, microscopy of paleobotanical samples, and analytical pyrolysis of fluvial sediments in Arlington Canyon on Santa Rosa Island by another group found no evidence of lonsdaleite or impact-induced fires.{{Cite journal |author-link=Andrew Cunningham Scott |vauthors=Scott AC, Hardiman M, Pinter N, Anderson RS, Daulton TL, Ejarque A, Finch P, Carter-champion A |year=2017 |title=Interpreting palaeofire evidence from fluvial sediments: a case study from Santa Rosa Island, California, with implications for the Younger Dryas Impact Hypothesis |url=https://researchportal.port.ac.uk/portal/en/publications/interpreting-palaeofire-evidence-from-fluvial-sediments(f8638df6-4a41-4fa7-b26f-c337e91253b1).html |url-status=live |journal=Journal of Quaternary Science |volume=32 |issue=1 |pages=35–47 |bibcode=2017JQS....32...35S |doi=10.1002/jqs.2914 |issn=0267-8179 |archive-url=https://web.archive.org/web/20200205000628/https://researchportal.port.ac.uk/portal/en/publications/interpreting-palaeofire-evidence-from-fluvial-sediments(f8638df6-4a41-4fa7-b26f-c337e91253b1).html |archive-date=5 February 2020 |access-date=5 February 2020 |s2cid=46954364}} Research published in 2012 has shown that the so-called "black mats" are easily explained by typical earth processes in wetland environments.{{efn|name=Pigati note|Pigati has noted that his 2012 paper{{hair space}} does not disprove the impact hypothesis.}}{{Cite journal |vauthors=Pigati JS, Latorre C, Rech JA, Betancourt JL, Martínez KE, Budahn JR |date=May 2012 |title=Accumulation of impact markers in desert wetlands and implications for the Younger Dryas impact hypothesis |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=109 |issue=19 |pages=7208–12 |bibcode=2012PNAS..109.7208P |doi=10.1073/pnas.1200296109 |pmc=3358914 |pmid=22529347 |doi-access=free}} This study of black mats, that are common in prehistorical wetland deposits which represent shallow marshlands, that were from 6000 to 40,000 years ago in the southwestern USA and Atacama Desert in Chile, showed elevated concentrations of iridium and magnetic sediments, magnetic spherules and titanomagnetite grains. It was suggested that because these markers are found within or at the base of black mats, irrespective of age or location, they likely arise from processes common to arid-climate wetland systems and not as a result of catastrophic bolide impacts.{{efn|name=Pigati note}}

Researchers have also criticized the conclusions of various studies for incorrect age-dating of the sediments,{{Cite journal |author-link2=Vance T. Holliday |author-link3=Jacquelyn Gill |vauthors=Blaauw M, Holliday VT, Gill JL, Nicoll K |date=August 2012 |title=Age models and the Younger Dryas Impact Hypothesis |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=109 |issue=34 |pages=E2240; author reply E2245–7 |bibcode=2012PNAS..109E2240B |doi=10.1073/pnas.1206143109 |pmc=3427088 |pmid=22829673 |doi-access=free}} contamination by modern carbon, inconsistent hypothesis that made it difficult to predict the type and size of bolide,{{Cite journal |author-link=Mark Boslough |vauthors=Boslough M |date=August 2012 |title=Inconsistent impact hypotheses for the Younger Dryas |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=109 |issue=34 |pages=E2241; author reply E2245–7 |bibcode=2012PNAS..109E2241B |doi=10.1073/pnas.1206739109 |pmc=3427067 |pmid=22829675 |doi-access=free}} lack of proper identification of lonsdaleite,{{Cite journal |vauthors=Daulton TL |date=August 2012 |title=Suspect cubic diamond "impact" proxy and a suspect lonsdaleite identification |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=109 |issue=34 |pages=E2242; author reply E2245–7 |bibcode=2012PNAS..109E2242D |doi=10.1073/pnas.1206253109 |pmc=3427052 |pmid=22829671 |doi-access=free}} confusing an extraterrestrial impact with other causes such as fire,{{Cite journal |author-link=Jacquelyn Gill |author-link2=Jessica L. Blois |author-link7=Andrew Cunningham Scott |author-link8=Cathy Whitlock |vauthors=Gill JL, Blois JL, Goring S, Marlon JR, Bartlein PJ, Nicoll K, Scott AC, Whitlock C |date=August 2012 |title=Paleoecological changes at Lake Cuitzeo were not consistent with an extraterrestrial impact |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=109 |issue=34 |pages=E2243; author reply E2245–7 |bibcode=2012PNAS..109E2243G |doi=10.1073/pnas.1206196109 |pmc=3427112 |pmid=22829674 |doi-access=free}} and for inconsistent use of the carbon spherule "proxy".{{Cite journal |author-link2=Andrew Cunningham Scott |author-link3=Margaret Collinson |vauthors=Hardiman M, Scott AC, Collinson ME, Anderson RS |date=August 2012 |title=Inconsistent redefining of the carbon spherule "impact" proxy |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=109 |issue=34 |pages=E2244; author reply E2245–7 |bibcode=2012PNAS..109E2244H |doi=10.1073/pnas.1206108109 |pmc=3427080 |pmid=22829672 |doi-access=free}} Naturally occurring lonsdaleite has also been identified in non-bolide diamond placer deposits in the Sakha Republic.

There is 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.{{Cite book |last=Haynes |first=Gary |title=American Megafaunal Extinctions at the End of the Pleistocene |year=2009 |isbn=978-1-4020-8792-9 |series=Vertebrate Paleobiology and Paleoanthropology |pages=1–20 |chapter=Introduction to the Volume |doi=10.1007/978-1-4020-8793-6_1 |name-list-style=vanc}}{{Cite book |last=Fiedel |first=Stuart |title=American Megafaunal Extinctions at the End of the Pleistocene |year=2009 |isbn=978-1-4020-8792-9 |series=Vertebrate Paleobiology and Paleoanthropology |pages=21–37 |chapter=Sudden Deaths: The Chronology of Terminal Pleistocene Megafaunal Extinction |doi=10.1007/978-1-4020-8793-6_2 |name-list-style=vanc}}{{Cite journal |vauthors=Hubbe A, Hubbe M, Neves W |date=September 2007 |title=Early Holocene survival of megafauna in South America |journal=Journal of Biogeography |volume=34 |issue=9 |pages=1642–1646 |doi=10.1111/j.1365-2699.2007.01744.x |doi-access=free|bibcode=2007JBiog..34.1642H }} The extinction of woolly mammoths in Siberia also appears to have occurred later than in North America. 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,{{Cite journal |vauthors=Stuart AJ, Kosintsev PA, Higham TF, Lister AM |date=October 2004 |title=Pleistocene to Holocene extinction dynamics in giant deer and woolly mammoth |journal=Nature |volume=431 |issue=7009 |pages=684–9 |bibcode=2004Natur.431..684S |doi=10.1038/nature02890 |pmid=15470427 |s2cid=4415073|url=http://doc.rero.ch/record/13494/files/PAL_E274.pdf }} and the survival of ground sloths in the Antilles,{{Cite book |last=Martin |first=Paul |title=Twilight of the mammoths: ice age extinctions and the rewilding of America |publisher=University of California Press |year=2005 |isbn=978-0-520-23141-2 |location=Berkeley |chapter=4 Ground Sloths at Home Cryptozoology, Ground Sloths, and Mapinguari National Park |chapter-url=https://archive.org/details/twilightofmammot00paul |name-list-style=vanc}} the Caribbean, until 4700 cal BP. The Australian megafaunal extinctions occurred approximately 30,000 years earlier than the hypothetical Younger Dryas event.{{Cite journal |last=Barnosky |first=Anthony D. |name-list-style=vanc |date=12 August 2008 |title=Colloquium paper: Megafauna biomass tradeoff as a driver of Quaternary and future extinctions |url=https://www.pnas.org/content/pnas/105/Supplement_1/11543.full.pdf |url-status=live |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=105 |issue=Supplement 1 |pages=11543–11548 |bibcode=2008PNAS..10511543B |doi=10.1073/pnas.0801918105 |pmc=2556404 |pmid=18695222 |archive-url=https://web.archive.org/web/20210619151410/https://www.pnas.org/content/pnas/105/Supplement_1/11543.full.pdf |archive-date=2021-06-19 |access-date=2021-07-06 |doi-access=free}}

The megafaunal extinction pattern observed in North America poses a problem for the bolide impact scenario since it raises the question of why large mammals should be preferentially exterminated over small mammals or other vertebrates.{{Cite journal |vauthors=Scott E |year=2010 |title=Extinctions, scenarios, and assumptions: Changes in latest Pleistocene large herbivore abundance and distribution in western North America |journal=Quaternary International |volume=217 |issue=1–2 |pages=225–239 |bibcode=2010QuInt.217..225S |doi=10.1016/j.quaint.2009.11.003}} Additionally, some extant megafaunal species such as bison and brown bear 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. Also, it appears that there was a collapse in North American megafaunal population from 14,800 to 13,700 BP, well before the date of the hypothetical extraterrestrial impact,{{Cite journal |author-link=Jacquelyn Gill |vauthors=Gill JL, Williams JW, Jackson ST, Lininger KB, Robinson GS |date=November 2009 |title=Pleistocene megafaunal collapse, novel plant communities, and enhanced fire regimes in North America |url=http://doc.rero.ch/record/210391/files/PAL_E4398.pdf |url-status=live |journal=Science |volume=326 |issue=5956 |pages=1100–3 |bibcode=2009Sci...326.1100G |doi=10.1126/science.1179504 |pmid=19965426 |archive-url=https://web.archive.org/web/20170922021056/http://doc.rero.ch/record/210391/files/PAL_E4398.pdf |archive-date=22 September 2017 |access-date=14 January 2019 |s2cid=206522597}} possibly from anthropogenic activities, including hunting.{{Cite journal |vauthors=Carrasco MA, Barnosky AD, Graham RW |date=December 2009 |title=Quantifying the extent of North American mammal extinction relative to the pre-anthropogenic baseline |journal=PLOS ONE |volume=4 |issue=12 |pages=e8331 |bibcode=2009PLoSO...4.8331C |doi=10.1371/journal.pone.0008331 |pmc=2789409 |pmid=20016820 |doi-access=free}}

A group in the Netherlands examined carbon-14 dates for charcoal particles that showed wildfires occurred well after the proposed impact date, and the glass-like carbon was produced by wildfires and no lonsdaleite was found.{{Cite journal |vauthors=van Hoesel A, Hoek WZ, Braadbaart F, van der Plicht J, Pennock GM, Drury MR |date=May 2012 |title=Nanodiamonds and wildfire evidence in the Usselo horizon postdate the Allerod-Younger Dryas boundary |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=109 |issue=20 |pages=7648–53 |bibcode=2012PNAS..109.7648V |doi=10.1073/pnas.1120950109 |pmc=3356666 |pmid=22547791 |doi-access=free}} Research at the Atacama Desert in Chile showed that silicate surface glasses were formed during at least two distinct periods at the end of the Pleistocene, separated by several hundred years.{{Cite journal |author-link3=Millarca Valenzuela |display-authors=8 |vauthors=Roperch P, Gattacceca J, Valenzuela M, Devouard B, Lorand JP, Arriagada C, Rochette P, Latorre C, Beck P |year=2017 |title=Surface vitrification caused by natural fires in Late Pleistocene wetlands of the Atacama Desert |url=https://hal.archives-ouvertes.fr/hal-02889687 |url-status=live |journal=Earth and Planetary Science Letters |volume=469 |pages=15–26 |bibcode=2017E&PSL.469...15R |doi=10.1016/j.epsl.2017.04.009 |issn=0012-821X |archive-url=https://web.archive.org/web/20210417234613/https://hal.archives-ouvertes.fr/hal-02889687 |archive-date=17 April 2021 |access-date=1 September 2020 |s2cid=55581133}}{{Update inline|reason=Further research has shown that this glass was formed by impacts — Schultz et al., 2021, Widespread glasses generated by cometary fireballs during the late Pleistocene in the Atacama Desert, Chile|date=December 2021}}

A study of Paleoindian demography found no evidence of a population decline among the Paleoindians at 12,900 ± 100 BP, which was inconsistent with predictions of an impact event,{{Cite journal |author-link=Vance T. Holliday |author-link2=David J. Meltzer |vauthors=Holliday VT, Meltzer DJ |date=October 2010 |title=The 12.9-ka ET Impact Hypothesis and North American Paleoindians |journal=Current Anthropology |volume=51 |issue=5 |pages=575–606 |doi=10.1086/656015 |s2cid=17823479}} suggesting that the hypothesis would probably need to be revised.{{Cite journal |vauthors=Buchanan B, Collard M, Edinborough K |date=August 2008 |title=Paleoindian demography and the extraterrestrial impact hypothesis |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=105 |issue=33 |pages=11651–4 |bibcode=2008PNAS..10511651B |doi=10.1073/pnas.0803762105 |pmc=2575318 |pmid=18697936 |doi-access=free}}{{Cite book |last=Haynes |first=Gary |url=https://books.google.com/books?id=iq6qZXUkWo0C&pg=PA125 |title=American megafaunal extinctions at the end of the Pleistocene |publisher=Springer Netherlands |year=2009 |isbn=978-1-4020-8792-9 |pages=125 |access-date=20 April 2012 |archive-url=https://web.archive.org/web/20200506222858/https://books.google.com/books?id=iq6qZXUkWo0C&pg=PA125 |archive-date=6 May 2020 |url-status=live |name-list-style=vanc}}{{text-source inline|date=May 2022}} A critique of this paper concluded that these results were an insensitive, low-fidelity population proxy incapable of detecting demographic change.{{Cite journal |last=Culleton |first=Brenda J. |name-list-style=vanc |date=16 Dec 2008 |title=Crude demographic proxy reveals nothing about Paleoindian population |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=105 |issue=50 |pages=E111; author reply E112–4 |bibcode=2008PNAS..105E.111C |doi=10.1073/pnas.0809092106 |pmc=2604924 |pmid=19073929 |doi-access=free}} The authors of a subsequent paper described three approaches to population dynamics in the Younger Dryas in North America, and concluded that there had been a significant decline and/or reorganisation in human population early in this period. The same paper also shows an apparent resurgence in population and/or settlements in the later Younger Dryas.{{Cite journal |last1=Anderson |first1=David G. |author-link=David G. Anderson |last2=Goodyear |first2=Albert |author-link2=Albert Goodyear |last3=Kennett |first3=James P. |author-link3=James P. Kennett |last4=West |first4=Allen |name-list-style=vanc |date=2011 |title=Multiple lines of evidence for possible Human population decline/settlement reorganization during the early Younger Dryas |journal=Quaternary International |volume=242 |issue=2 |pages=570–583 |bibcode=2011QuInt.242..570A |doi=10.1016/j.quaint.2011.04.020}} A 2022 study by an independent group presents genomic evidence that a previously unidentified pre-18,000 BP South American population suffered a major disruption at the Younger Dryas onset, resulting in a significant loss of lineages and a Y chromosome bottleneck.{{cite journal |last1=Sepulveda |first1=Paula B. Paz |last2=Mayordomo |first2=Andrea C. |last3=Sala |first3=Camille |last4=Sosa |first4=Ezequiel J. |last5=Zaiat |first5=Jonathan J. |last6=Cuello |first6=Mariela |last7=Schwab |first7=Marisol |last8=Golpe |first8=Danielaa R. |last9=Aquilano |first9=Eliana |last10=Santos |first10=Maria R. |last11=Dipierri |first11=Jose E. |last12=Gomez |first12=Emma L. A. |last13=Bravi |first13=Claudio M. |last14=Muzzio |first14=Marina |last15=Bailliet |first15=Graciela |name-list-style=vanc |date=2022 |title=Human Y chromosome sequences from Q Haplogroup reveal a South American settlement pre-18,000 years ago and a profound genomic impact during the Younger Dryas |journal=PLOS ONE |language=en |volume=17 |issue=8 |pages=e0271971 |bibcode=2022PLoSO..1771971P |doi=10.1371/journal.pone.0271971 |pmc=9385064 |pmid=35976870 |doi-access=free}}

File:Hiawatha v45 scene1 4k 5mtopo.1760.tif with the ice sheet removed to show the surface of bedrock in the region around the Hiawatha Glacier]]

A 2018 paper reported the discovery of an impact crater under the Hiawatha Glacier in Greenland of unknown age.{{Cite journal |display-authors=8 |vauthors=Kjær KH, Larsen NK, Binder T, Bjørk AA, Eisen O, Fahnestock MA, Funder S, Garde AA, Haack H, Helm V, Houmark-Nielsen M, Kjeldsen KK, Khan SA, Machguth H, McDonald I, Morlighem M, Mouginot J, Paden JD, Waight TE, Weikusat C, Willerslev E, MacGregor JA |date=November 2018 |title=A large impact crater beneath Hiawatha Glacier in northwest Greenland |journal=Science Advances |volume=4 |issue=11 |pages=eaar8173 |bibcode=2018SciA....4.8173K |doi=10.1126/sciadv.aar8173 |pmc=6235527 |pmid=30443592 |doi-access=free}} Kurt Kjær, the lead author of the paper, speculated that it might date to the Pleistocene (2.58 million to 11,700 years ago), and mentioned a possible connection to the Younger Dryas.{{Cite web |last=Voosen |first=Paul |name-list-style=vanc |date=14 November 2018 |title=Massive crater under Greenland's ice points to climate-altering impact in the time of humans |url=https://www.science.org/content/article/massive-crater-under-greenland-s-ice-points-climate-altering-impact-time-humans |url-status=live |archive-url=https://web.archive.org/web/20190113194450/https://www.sciencemag.org/news/2018/11/massive-crater-under-greenland-s-ice-points-climate-altering-impact-time-humans |archive-date=13 January 2019 |access-date=13 January 2019 |website=Sciencemag.org |publisher=Science}}

However, in 2022 the crater was dated to around 58 million years ago, the late Paleocene, using Argon–argon dating combined with uranium–lead dating of shocked zircon crystals.{{efn|This paper's co-authors include Kurt Kjær and Elizabeth Silber}}{{Cite press release |title=Giant impact crater in Greenland occurred a few million years after dinosaurs went extinct |date=2022-03-09 |publisher=University of Copenhagen |url=https://news.ku.dk/all_news/2022/03/giant-impact-crater-in-greenland-occurred-a-few-million-years-after-dinosaurs-went-extinct/ |access-date=2022-03-10 |url-status=live |archive-url=https://web.archive.org/web/20220309192942/https://news.ku.dk/all_news/2022/03/giant-impact-crater-in-greenland-occurred-a-few-million-years-after-dinosaurs-went-extinct/ |archive-date=2022-03-09}}{{Cite Q |Q111179348 |last1=Kenny |first1=Gavin G. |last2=Hyde |first2=William R. |last3=Storey |first3=Michael |last4=Garde |first4=Adam A. |last5=Whitehouse |first5=Martin J. |last6=Beck |first6=Pierre |last7=Johansson |first7=Leif |last8=Søndergaard |first8=Anne Sofie |last9=Bjørk |first9=Anders A. |last10=MacGregor |first10=Joseph A. |last11=Khan |first11=Shfaqat A. |last12=Mouginot |first12=Jérémie |last13=Johnson |first13=Brandon C. |last14=Silber |first14=Elizabeth A. |last15=Wielandt |first15=Daniel K. P. |last16=Kjær |first16=Kurt H. |last17=Larsen |first17=Nicolaj K. |name-list-style=vanc |display-authors=8}}

{{Main|Younger Dryas#Causes}}

A number of other hypotheses have been put forward about the cause of the Younger Dryas climate event.

The most widely accepted explanation is that it began because of a significant reduction or shutdown of the North Atlantic "Conveyor" – which circulates warm tropical waters northward – as the consequence of deglaciation in North America. Geological evidence for such an event is not fully secure,{{cite journal |last=Broecker |first=Wallace S. |year=2006 |title=Was the Younger Dryas triggered by a flood? |journal=Science |volume=312 |issue=5777 |pages=1146–1148 |doi=10.1126/science.1123253 |pmid=16728622 |s2cid=39544213}} but recent work has identified a pathway along the Mackenzie River that would have spilled fresh water from Lake Agassiz into the Arctic and thence into the Atlantic.{{cite journal |last1=Murton |first1=Julian B. |last2=Bateman |first2=Mark D. |last3=Dallimore |first3=Scott R. |last4=Teller |first4=James T. |last5=Yang |first5=Zhirong |date=2010 |title=Identification of Younger Dryas outburst flood path from Lake Agassiz to the Arctic Ocean |journal=Nature |language=en |volume=464 |issue=7289 |pages=740–743 |bibcode=2010Natur.464..740M |doi=10.1038/nature08954 |issn=0028-0836 |pmid=20360738 |s2cid=4425933}}{{cite journal |last1=Keigwin |first1=L.D. |last2=Klotsko |first2=S. |last3=Zhao |first3=N. |last4=Reilly |first4=B. |last5=Giosan |first5=L. |last6=Driscoll |first6=N.W. |date=2018 |title=Deglacial floods in the Beaufort Sea preceded Younger Dryas cooling |journal=Nature Geoscience |language=en |volume=11 |issue=8 |pages=599–604 |bibcode=2018NatGe..11..599K |doi=10.1038/s41561-018-0169-6 |issn=1752-0894 |hdl-access=free |hdl=1912/10543 |s2cid=133852610}} The global climate would then have become locked into the new state until freezing removed the fresh water "lid" from the North Atlantic.

Although initially sceptical, Wallace Broecker—the scientist who proposed the conveyor shutdown hypothesis—eventually agreed with the idea of an extraterrestrial impact at the Younger Dryas boundary, and thought that it had acted as a trigger on top of a system that was already approaching instability.{{efn|Broecker did not believe that the impact caused extinctions.}}{{Cite Q |Q107575586 |last=Broecker |first=Wallace S. |author-link=Wallace Smith Broecker |name-list-style=vanc |url-status=live}}

Another hypothesis suggests instead that the jet stream shifted northward in response to the melting of the North American ice sheet, which brought more rain to the North Atlantic, which freshened the ocean surface enough to slow the thermohaline circulation.{{cite journal |last1=Eisenman |first1=I. |last2=Bitz |first2=C.M. |author2-link=Cecilia Bitz |last3=Tziperman |first3=E. |year=2009 |title=Rain driven by receding ice sheets as a cause of past climate change |journal=Paleoceanography |volume=24 |issue=4 |page=PA4209 |bibcode=2009PalOc..24.4209E |doi=10.1029/2009PA001778 |doi-access=free |s2cid=6896108}}

Another proposed cause has been volcanic activity.{{Cite press release |title=Texas Cave Sediment Upends Meteorite Explanation for Global Cooling |date=2020-07-31 |publisher=Baylor University |location=Waco, Texas |url=https://www.baylor.edu/mediacommunications/news.php?action=story&story=219716 |access-date=2021-08-03 |url-status=live |archive-url=https://web.archive.org/web/20210601090925/https://www.baylor.edu/mediacommunications/news.php?action=story&story=219716 |archive-date=2021-06-01}}{{sfnp|Sun|Brandon|Forman|Waters|2020}} However, this has been challenged recently due to improved dating of the most likely suspect, the Laacher See volcano. In 2021, research by Frederick Reinig et al. precisely dated the eruption to 200 ± 21 years before the onset of the Younger Dryas, therefore ruling it out as a culprit.{{Cite Q|Q107389873|last=Reinig|first=Frederick|last2=Wacker|first2=Lukas|last3=Jöris|first3=Olaf|last4=Oppenheimer|first4=Clive|last5=Guidobaldi|first5=Giulia|last6=Nievergelt|first6=Daniel|last7=Adolphi|first7=Florian|last8=Cherubini|first8=Paolo|last9=Engels|first9=Stefan|last10=Esper|first10=Jan|last11=Land|first11=Alexander|last12=Lane|first12=Christine|last13=Pfanz|first13=Hardy|last14=Remmele|first14=Sabine|last15=Sigl|first15=Michael|last16=Sookdeo|first16=Adam|last17=Büntgen|first17=Ulf|display-authors=6|name-list-style=vanc|quote=[Measurements] firmly date the [Laacher See eruption] to 13,006 ± 9 calibrated years before present (BP; taken as AD 1950), which is more than a century earlier than previously accepted. ...thereby dating the onset of the Younger Dryas to 12,807 ± 12 calibrated years BP, which is around 130 years earlier than thought.}} The same study also concluded that the onset took place synchronously over the entire North Atlantic and Central European region. A press release from the University of Mainz stated, "Due to the new dating, the European archives now have to be temporally adapted. At the same time, a previously existing temporal difference to the data from the Greenland ice cores was closed."{{Cite press release |title=Eruption of the Laacher See volcano redated |date=2021-07-01 |url=https://www.uni-mainz.de/presse/aktuell/13879_ENG_HTML.php |access-date=2021-08-26 |url-status=live |archive-url=https://web.archive.org/web/20210701165741/https://www.uni-mainz.de/presse/aktuell/13879_ENG_HTML.php |archive-date=2021-07-01 |website=University of Mainz |quote=That is 126 years earlier than the generally accepted dating based on sediments in the Meerfelder Maar from the Eifel region in Germany. ... This difference has far-reaching consequences for the synchronization of European climate archives and the understanding of North Atlantic and European climate history. ... This means that the [onset of the Younger Dryas] also occurred in Central Europe 130 years earlier, around 12,870 years ago respectively. This is in line with the onset of the cooling in the North Atlantic region identified in ice cores from Greenland. ... 'This strong cooling did not take place time transgressively, as previously thought, but rather synchronously over the entire North Atlantic and Central European region,' said Frederick Reinig.}}

{{primary sources|section|date=October 2022}}

The idea that a comet struck North America at the end of the last ice age was first proposed as a speculative premise by the American congressman and pseudohistorian Ignatius Donnelly in 1883, who suggested it formed the Great Lakes and caused a sudden extreme cold period, which devastated animal and human populations.

In 2001, Richard Firestone and William Topping published their first version of the YDIH, "Terrestrial Evidence of a Nuclear Catastrophe in Paleoindian Times" in Mammoth Trumpet, a newsletter of the Center for the Study of the First Americans.{{cite journal |last1=Firestone |first1=Richard B. |last2=Topping |first2=William |title=Terrestrial Evidence of a Nuclear Catastrophe in Paleoindian Times |journal=Mammoth Trumpit |date=March 2001 |volume=16 |issue=2 |pages=9–16 |url=https://liberalarts.tamu.edu/wp-content/uploads/sites/14/2019/08/vol16_num2.pdf |access-date=31 January 2023}} They proposed that "the entire Great Lakes region (and beyond) was subjected to a particle bombardment and a catastrophic nuclear radiation..." They argue that this cataclysm generated a shock wave that gouged out the Carolina Bays and reset the radiocarbon clock. Most geologists today interpret the Carolina bays as relict geomorphological features that developed via various eolian and lacustrine processes. Multiple lines of evidence, e.g. radiocarbon dating, optically stimulated luminescence dating, and palynology, indicate that the Carolina bays predate the start of the Holocene. Fossil pollen recovered from cores of undisturbed sediment taken from various Carolina bays in North Carolina by Frey,{{cite journal|jstor=1943595|doi=10.2307/1943595|title=Regional Aspects of the Late-Glacial and Post-Glacial Pollen Succession of Southeastern North Carolina|year=1953|last1=Frey|first1=David G.|journal=Ecological Monographs|volume=23|issue=3|pages=289–313|bibcode=1953EcoM...23..289F }}{{cite journal|doi=10.2307/1931316|jstor=1931316|title=A Time Revision of the Pleistocene Pollen Chronology of Southeastern North Carolina|year=1955|last1=Frey|first1=David G.|journal=Ecology|volume=36|issue=4|pages=762–763|bibcode=1955Ecol...36..762F }}

Watts,{{cite journal |doi=10.1016/0033-5894(80)90028-9 |title=Late-Quaternary Vegetation History at White Pond on the Inner Coastal Plain of South Carolina |year=1980 |last1=Watts |first1=W. A. |journal=Quaternary Research |volume=13 |issue=2 |pages=187–199 |bibcode=1980QuRes..13..187W |s2cid=140654499 }} and Whitehead{{cite journal |doi=10.2307/1934924 |jstor=1934924 |title=Fossil Pine Pollen and Full-Glacial Vegetation in Southeastern North Carolina |year=1964 |last1=Whitehead |first1=Donald R. |journal=Ecology |volume=45 |issue=4 |pages=767–777 |bibcode=1964Ecol...45..767W }}{{cite journal |doi=10.2307/2937324 |jstor=2937324 |title=Late-Pleistocene Vegetational Changes in Northeastern North Carolina |year=1981 |last1=Whitehead |first1=Donald R. |journal=Ecological Monographs |volume=51 |issue=4 |pages=451–471 |bibcode=1981EcoM...51..451W }} document the presence of full glacial pollen zones within the sediments filling some Carolina bays. The range of dates can be interpreted that Carolina bays were either created episodically over the last tens of thousands of years or were created at time over a hundred thousand years ago and have since been episodically modified.{{cite journal |doi=10.1002/(SICI)1520-6548(199610)11:6<481::AID-GEA2>3.0.CO;2-4 |title=Carolina Bay geoarchaeology and Holocene landscape evolution on the Upper Coastal Plain of South Carolina |year=1996 |last1=Brooks |first1=Mark J. |last2=Taylor |first2=Barbara E. |last3=Grant |first3=John A. |journal=Geoarchaeology|volume=11 |issue=6 |pages=481–504|bibcode=1996Gearc..11..481B }}{{cite journal |author=Brooks, M. J. |year=2001 |title=Pleistocene encroachment of the Wateree River sand sheet into Big Bay on the Middle Coastal Plain of South Carolina |journal= Southeastern Geology |volume= 40 |pages=241–257}}{{cite journal |doi=10.1016/S0169-555X(97)00074-3 |title=New constraints on the evolution of Carolina Bays from ground-penetrating radar |year=1998 |last1=Grant |first1=John A. |last2=Brooks |first2=Mark J. |last3=Taylor |first3=Barbara E. |journal=Geomorphology |volume=22 |issue=3–4 |pages=325–345|bibcode=1998Geomo..22..325G}} Recent work by the U.S. Geological Survey{{cite book |last1=Swezey |first1= C. S. |chapter= Quaternary Eolian Dunes and Sand Sheets in Inland Locations of the Atlantic Coastal Plain Province, USA |date=2020 |title=Inland Dunes of North America |series= Dunes of the World |editor-first1=N. |editor-last1= Lancaster |editor-first2=P. |editor-last2=Hesp |publisher=Springer Publishing |pages=11–63 |doi=10.1007/978-3-030-40498-7_2 |isbn=978-3-030-40498-7 |s2cid= 219502764}} has interpreted the Carolina bays as relict thermokarst lakes that have been modified by eolian and lacustrine processes. Modern thermokarst lakes are common today around Barrow (Alaska), and the long axes of these lakes are oblique to the prevailing wind direction.

In 2006, The Cycle of Cosmic Catastrophes: How a Stone-Age Comet Changed the Course of World Culture, a trade book by Richard Firestone, Allen West and Simon Warwick-Smith, was published by Inner Traditions – Bear & Company and marketed in the category of Earth Changes. It proposed that a large meteor air burst or impact of one or more comets initiated the Younger Dryas cold period about 12,900 BP calibrated (10,900 ¹⁴C uncalibrated) years ago.{{Cite book |last1=Firestone |first1=Richard |url=https://archive.org/details/cycleofcosmiccat0000fire/page/392 |title=The Cycle of Cosmic Catastrophes: How a Stone-Age comet changed the course of world culture |last2=West |first2=Allen |last3=Warwick-Smith |first3=Simon |date=4 June 2006 |publisher=Bear & Company |isbn=978-1591430612 |name-list-style=vanc}}

In May 2007, at a meeting of the American Geophysical Union in Acapulco, Firestone, West, and around twenty other scientists made their first formal presentation of the hypothesis.{{Cite news |last=Gramling |first=Carolyn |name-list-style=vanc |date=2018-06-26 |title=Why won't this debate about an ancient cold snap die? |language=en-US |work=Science News |url=https://www.sciencenews.org/article/younger-dryas-comet-impact-cold-snap |url-status=live |access-date=2021-08-21 |archive-url=https://web.archive.org/web/20210805112551/https://www.sciencenews.org/article/younger-dryas-comet-impact-cold-snap |archive-date=2021-08-05 |quote=The first formal description of the Younger Dryas impact hypothesis came in 2007, when four researchers sat in front of a gaggle of reporters at the American Geophysical Union's spring meeting in Acapulco, Mexico.}} Later that year, the group published a paper in the Proceedings of the National Academy of Sciences (PNAS) that suggested the impact event may have led to an immediate decline in human populations in North America. Since this paper was considered too controversial for standard peer review, it was handled by a specially selected 'personal editor' who was friendly to the hypothesis.

In 2008, C. Vance Haynes Jr. published data to support the synchronous nature of the black mats,{{efn|name=Black mat note}} emphasizing that independent analysis of other Clovis sites was required to support the hypothesis. He was skeptical of the bolide impact as the cause of the Younger Dryas and associated megafauna extinction but concluded "... something major happened at 10,900 YBP (¹⁴C uncalibrated) that we have yet to understand."{{Cite journal |author-link=Vance Haynes |vauthors=Haynes CV |date=May 2008 |title=Younger Dryas "black mats" and the Rancholabrean termination in North America |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=105 |issue=18 |pages=6520–6525 |bibcode=2008PNAS..105.6520H |doi=10.1073/pnas.0800560105 |pmc=2373324 |pmid=18436643|doi-access=free }} The first debate between proponents and skeptics was held at the 2008 Pecos Conference in Flagstaff, Arizona.{{cite AV media |url=https://www.youtube.com/watch?v=vyz7Lcvamu4|website=YouTube|title= Pecos Conference 2008 Comet Impact Debate|year=2008}}{{Cite web |title=2008 Pecos Conference |url=http://www.swanet.org/2008_pecos_conference/related.html |url-status=live |archive-url=https://web.archive.org/web/20190803211311/http://www.swanet.org/2008_pecos_conference/related.html |archive-date=3 August 2019 |access-date=3 August 2019 |website=swanet.org}}

In 2009, papers by Kerr{{Cite journal |author-link=Richard Kerr (science journalist) |vauthors=Kerr RA |date=January 2009 |title=Planetary impacts. Did the mammoth slayer leave a diamond calling card? |url=http://doc.rero.ch/record/16089/files/PAL_E3880.pdf |journal=Science |volume=323 |issue=5910 |pages=26 |doi=10.1126/science.323.5910.26 |pmid=19119192 |s2cid=29639618}} and Kennett{{Cite journal |author-link2=James P. Kennett |display-authors=8 |vauthors=Kennett DJ, Kennett JP, West A, Mercer C, Hee SS, Bement L, Bunch TE, Sellers M, Wolbach WS |date=January 2009 |title=Nanodiamonds in the Younger Dryas boundary sediment layer |url=http://doc.rero.ch/record/16088/files/PAL_E3879.pdf |journal=Science |volume=323 |issue=5910 |pages=94 |bibcode=2009Sci...323...94K |doi=10.1126/science.1162819 |pmid=19119227 |s2cid=206514910}} in the journal Science asserted that nanodiamonds were evidence for a swarm of carbonaceous chondrites or comet fragments from air burst(s) or impact(s) that set parts of North America on fire, caused the extinction of most of the megafauna in North America, and led to the demise of the Clovis culture A special debate-style session was convened at the 2009 AGU Fall Meeting in which skeptics and supporters alternated in giving presentations.{{Cite web |title=Younger Dryas Boundary: Extraterrestrial Impact or Not? I Posters |url=http://abstractsearch.agu.org/meetings/2009/FM/PP31D.html |url-status=live |archive-url=https://web.archive.org/web/20190803211620/http://abstractsearch.agu.org/meetings/2009/FM/PP31D.html |archive-date=2019-08-03 |access-date=2021-06-09 |website=abstractsearch.agu.org |series=2009 AGU Fall Meeting |id=PP31D}}

{{Cite web |title=Younger Dryas Boundary: Extraterrestrial Impact or Not? II |url=http://abstractsearch.agu.org/meetings/2009/FM/PP33B.html |url-status=live |archive-url=https://web.archive.org/web/20210429184719/https://abstractsearch.agu.org/meetings/2009/FM/PP33B.html |archive-date=2021-04-29 |access-date=2021-06-09 |website=abstractsearch.agu.org |series=2009 AGU Fall Meeting |id=PP33B}}

{{anchor|Taurids}}

In 2010, astronomer William Napier published a model suggesting that fragments of a comet—initially 50 to 100 kilometers in diameter—could have been responsible for such an impact, and that the Taurid complex is formed of the remaining debris.

{{anchor|Requiem}}

In 2011, Pinter and others challenged the Younger Dryas impact hypothesis on the basis that most of the conclusions could not be reproduced and were a misinterpretation of data. Skepticism increased when it was reported that one of the lead authors of the original paper had practiced geophysics without a license.{{efn|Allen West had the conviction expunged after the matter was reported on by Rex Dalton.}}{{Cite web |date=2002-06-06 |title=Enforcement Action |url=http://www.geology.ca.gov/consumers/enforcement/jonkerwhitt.shtml |url-status=dead |archive-url=https://web.archive.org/web/20120408205803/http://www.geology.ca.gov/consumers/enforcement/jonkerwhitt.shtml |archive-date=2012-04-08 |website=California Department of Consumer Affairs - Board for Professional Engineers, Land Surveyors, and Geologists |quote=The Board's inquiry concluded that Kevin Lee Jonker and Allen Whitt had practiced geophysics without a license.}} Around that time, Daulton stated that no nanodiamonds were found and that the supposed carbon spherules could be fungus or insect feces and included modern contaminants as stated by Boslough and others{{Cite book |title=Climates, Landscapes, and Civilizations |vauthors=Boslough M, Nicoll K, Holliday V, Daulton TL, Meltzer D, Pinter N, Scott AC, Surovell T, Claeys P, Gill J, Paquay F, Marlon JR, Bartlein PJ, Whitlock CL, Grayson D, Jull AJ |year=2013 |isbn=9781118704325 |veditors=Giosan L, Fuller DQ, Nicoll K, Flad RK, Clift PD |series=Geophysical Monograph Series |pages=13–26 |chapter=Arguments and Evidence Against a Younger Dryas Impact Event |doi=10.1029/2012GM001209 |display-authors=8 |author-link=Mark Boslough |author-link3=Vance T. Holliday |author-link5=David J. Meltzer |author-link7=Andrew Cunningham Scott |author-link10=Jacquelyn Gill |author-link14=Cathy Whitlock |author-link16=A.J. Timothy Jull}} and Roach. In response, in June 2013 Wittke and others published a re-evaluation of spherules from eighteen sites worldwide that they interpret as supporting their hypothesis.

In 2012, a paper by Bunch and others reported the discovery of scoria like objects (SLO) and stated that they were consistent with an extraterrestrial impact or airburst.{{Cite journal |author-link3=Andrew M. T. Moore |author-link9=Gordon Hillman |author-link18=James P. Kennett |display-authors=8 |vauthors=Bunch TE, Hermes RE, Moore AM, Kennett DJ, Weaver JC, Wittke JH, DeCarli PS, Bischoff JL, Hillman GC, Howard GA, Kimbel DR, Kletetschka G, Lipo CP, Sakai S, Revay Z, West A, Firestone RB, Kennett JP |date=July 2012 |title=Very high-temperature impact melt products as evidence for cosmic airbursts and impacts 12,900 years ago |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=109 |issue=28 |pages=E1903–E1912 |bibcode=2012PNAS..109E1903B |doi=10.1073/pnas.1204453109 |pmc=3396500 |pmid=22711809|doi-access=free }} Post-publication review of this paper suggests that at least some of these SLOs are anthropogenic.{{cite journal|display-authors=8 |vauthors=Bunch TE, Hermes RE, Moore AM, Kennett DJ, Weaver JC, Wittke JH, DeCarli PS, Bischoff JL, Hillman GC, Howard GA, Kimbel DR, Kletetschka G, Lipo CP, Sakai S, Revay Z, West A, Firestone RB, Kennett JP |date=July 2012 |title=Very high-temperature impact melt products as evidence for cosmic airbursts and impacts 12,900 years ago |url=https://pubpeer.com/publications/7031153F4F3B5EB62FA7EE5B6FD9E3|access-date=2022-08-15 |website=PubPeer}} Another group of scientists reported evidence supporting a modified version of the hypothesis—involving a fragmented comet or asteroid—was found in lake bed cores dating to 12,900 YBP from Lake Cuitzeo in Guanajuato, Mexico. It 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.{{Cite journal |display-authors=8 |author-link11=James P. Kennett |vauthors=Israde-Alcántara I, Bischoff JL, Domínguez-Vázquez G, Li HC, DeCarli PS, Bunch TE, Wittke JH, Weaver JC, Firestone RB, West A, Kennett JP, Mercer C, Xie S, Richman EK, Kinzie CR, Wolbach WS |date=March 2012 |title=Evidence from central Mexico supporting the Younger Dryas extraterrestrial impact hypothesis |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=109 |issue=13 |pages=E738–E747 |bibcode=2012PNAS..109E.738I |doi=10.1073/pnas.1110614109 |pmc=3324006 |pmid=22392980|doi-access=free}} Lonsdaleite has also been made artificially in laboratories.{{Cite journal |vauthors=Bundy FP |year=1967 |title=Hexagonal Diamond—A New Form of Carbon |journal=The Journal of Chemical Physics |volume=46 |issue=9 |pages=3437–3446 |bibcode=1967JChPh..46.3437B |doi=10.1063/1.1841236}}{{Cite journal|display-authors=8 |vauthors=Kaminskii FV, Blinova GK, Galimov EM, Gurkina GA, Klyuev YA, Kodina LA, Koptil VI, Krivonos VF, Frolova FN, Khrenov AY |year=1985 |title=Polycrystalline aggregates of diamond with lonsdaleite from Yakutian [Sakhan] placers |url=https://www.researchgate.net/publication/284295851 |url-status=live |journal=Mineral Zhurnal |volume=7 |pages=27–36 |archive-url=https://web.archive.org/web/20181023234301/https://www.researchgate.net/publication/284295851 |archive-date=23 October 2018 |access-date=1 July 2017}}{{Relevance inline |sentence |reason=Why does it matter that synthetic lonsdaleite can me made in laboratories? |date=July 2021}}

In 2013, Petaev and others reported a hundredfold spike in the concentration of platinum in Greenland ice cores roughly dated to 12,890 YBP.{{Cite journal |vauthors=Petaev MI, Huang S, Jacobsen SB, Zindler A |date=August 2013 |title=Large Pt [platinum] anomaly in the Greenland ice core points to a cataclysm at the onset of Younger Dryas |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=110 |issue=32 |pages=12917–12920 |bibcode=2013PNAS..11012917P |doi=10.1073/pnas.1303924110 |pmc=3740870 |pmid=23878232|doi-access=free }} This anomaly was attributed to a small local iron meteorite fall without any widespread consequences.{{Cite journal |last=Boslough |first=Mark |author-link=Mark Boslough |name-list-style=vanc |date=December 2013 |title=Greenland Pt [platinum] anomaly may point to non-cataclysmic Cape York meteorite entry |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=110 |issue=52 |page=E5035 |bibcode=2013PNAS..110E5035B |doi=10.1073/pnas.1320328111 |pmc=3876257 |pmid=24347646|doi-access=free }} A refutation of the YDIH, by Holliday and others (including Petaev), showed that the Pt spike was not evidence to support the YDIH because it occurred 20 years after the YDB.

In 2016, Holiday and others reported on further analysis of Younger Dryas boundary sediments at nine sites found no evidence of an extraterrestrial impact at the Younger Dryas boundary.{{Cite journal|author-link=Vance T. Holliday |vauthors=Holliday V, Surovell T, Johnson E |date=2016-07-08 |title=A Blind Test of the Younger Dryas Impact Hypothesis |journal=PLOS ONE |volume=11 |issue=7 |pages=e0155470 |bibcode=2016PLoSO..1155470H |doi=10.1371/journal.pone.0155470 |pmc=4938604 |pmid=27391147|doi-access=free}} Also that year, Daulton and others reported an analysis of nanodiamond evidence failed to uncover lonsdaleite or a spike in nanodiamond concentration at the {{abbr|YDB|Younger Dryas boundary}}.{{Cite journal|last1=Daulton |first1=Tyrone L. |last2=Amari |first2=Sachiko |last3=Scott |first3=Andrew C. |author-link3=Andrew Cunningham Scott |last4=Hardiman |first4=Mark |last5=Pinter |first5=Nicholas |last6=Anderson |first6=R. Scott |name-list-style=vanc |date=2016-12-19 |title=Comprehensive analysis of nanodiamond evidence relating to the Younger Dryas Impact Hypothesis |url=https://researchportal.port.ac.uk/portal/en/publications/comprehensive-analysis-of-nanodiamond-evidence-reported-to-support-the-younger-dryas-impact-hypothesis(f675f063-5d32-4cac-9b83-e7ce6a9432d6).html |url-status=live |journal=Journal of Quaternary Science |volume=32 |issue=1 |pages=7–34 |bibcode=2017JQS....32....7D |doi=10.1002/jqs.2892 |archive-url=https://web.archive.org/web/20200205000623/https://researchportal.port.ac.uk/portal/en/publications/comprehensive-analysis-of-nanodiamond-evidence-reported-to-support-the-younger-dryas-impact-hypothesis(f675f063-5d32-4cac-9b83-e7ce6a9432d6).html |archive-date=5 February 2020 |access-date=5 February 2020 |doi-access=free}}

In 2017, C R Moore and others reported a Pt anomaly at eleven continental sites dated to the Younger Dryas, which is linked with the Greenland Platinum anomaly.{{Cite journal|author-link6=Albert Goodyear |author-link10=James P. Kennett |display-authors=8 |vauthors=Moore CR, West A, LeCompte MA, Brooks MJ, Daniel IR, Goodyear AC, Ferguson TA, Ivester AH, Feathers JK, Kennett JP, Tankersley KB, Adedeji AV, Bunch TE |date=March 2017 |title=Widespread platinum anomaly documented at the Younger Dryas onset in North American sedimentary sequences |journal=Scientific Reports |volume=7 |issue=1 |page=44031 |bibcode=2017NatSR...744031M |doi=10.1038/srep44031 |pmc=5343653 |pmid=28276513}}

In 2018, dealing with an "extraordinary biomass-burning episode" associated with the Younger Dryas Impact were reported by Wolbach and others{{Cite journal|display-authors=8 |vauthors=Wolbach WS, Ballard JP, Mayewski PA, Adedeji V, Bunch TE, Firestone RB, French TA, Howard GA, Israde-Alcántara I, Johnson JR, Kimbel D, etal |date=March 2018 |title=Extraordinary biomass-burning episode and impact winter triggered by the Younger Dryas cosmic impact ~12,800 years ago. Part 1. Ice Cores and Glaciers |journal=Journal of Geology |volume=126 |issue=2 |pages=165–184 |bibcode=2018JG....126..165W |doi=10.1086/695703 |s2cid=53021110}}{{Cite journal |author-link9=Jon M. Erlandson |display-authors=8 |vauthors=Wolbach WS, Ballard JP, Mayewski PA, Parnell AC, Cahill N, Adedeji V, Bunch TE, Domínguez-Vázquez G, Erlandson JM, Firestone RB, French TA, etal |date=March 2018 |title=Extraordinary biomass-burning episode and impact winter triggered by the Younger Dryas cosmic impact ~12,800 years ago. Part 2. Lake, Marine, and Terrestrial Sediments |url=http://mural.maynoothuniversity.ie/13277/1/AP_hamilton_extraordinary.pdf |url-status=live |journal=Journal of Geology |volume=126 |issue=2 |pages=185–205 |bibcode=2018JG....126..185W |doi=10.1086/695704 |archive-url=https://web.archive.org/web/20201104002502/http://mural.maynoothuniversity.ie/13277/1/AP_hamilton_extraordinary.pdf |archive-date=4 November 2020 |access-date=10 November 2020 |s2cid=53494648}} and Lynch.{{Cite press release|title=New research suggests toward end of Ice Age, human beings witnessed fires larger than dinosaur killer, thanks to a cosmic impact |date=2018-02-01 |url=https://news.ku.edu/2018/01/30/new-research-suggests-toward-end-ice-age-human-beings-witnessed-fires-larger-dinosaur |last1=Lynch |first1=Brendan M. |access-date=2021-12-14 |url-status=live |archive-url=https://web.archive.org/web/20210526014433/https://news.ku.edu/2018/01/30/new-research-suggests-toward-end-ice-age-human-beings-witnessed-fires-larger-dinosaur |archive-date=2021-05-26 |name-list-style=vanc |website=University of Kansas}} However, these claims of extraordinary fires are disputed by Holliday and others{{Cite Q |Q91978737 |author-link1=Vance T. Holliday |author-link3=Andrew Cunningham Scott |last1=Holliday |first1=Vance T. |last2=Bartlein |first2=Patrick J. |last3=Scott |first3=Andrew C. |last4=Marlon |first4=Jennifer R. |name-list-style=vanc}} with a response by Wolbach.{{Cite Q |Q91978742 |author-link11=Adrian Melott |author-link13=William Napier (astronomer) |author-link20=James P. Kennett |last1=Wolbach |first1=Wendy S. |last2=Ballard |first2=Joanne P. |last3=Mayewski |first3=Paul A. |last4=Kurbatov |first4=Andrei |last5=Bunch |first5=Ted E. |last6=LeCompte |first6=Malcolm A. |last7=Adedeji |first7=Victor |last8=Israde-Alcántara |first8=Isabel |last9=Firestone |first9=Richard B. |last10=Mahaney |first10=William C. |last11=Melott |first11=Adrian L. |last12=Moore |first12=Christopher R. |last13=Napier |first13=William M. |last14=Howard |first14=George A. |last15=Tankersley |first15=Kenneth B. |last16=Thomas |first16=Brian C. |last17=Wittke |first17=James H. |last18=Johnson |first18=John R. |last19=Mitra |first19=Siddhartha |last20=Kennett |first20=James P. |last21=Kletetschka |first21=Gunther |last22=West |first22=Allen |display-authors=8 |name-list-style=vanc}}

File:Younger Dryas boundary sites.png et al. 2019{{hair space}}{{sfnp|Pino|Abarzúa|Astorga|Martel-Cea|2019}} showing 53 Younger Dryas boundary sites. Orange dots represent 28 sites with peaks in both platinum (Pt) and other impact proxies such as high-temperature Fe-rich spherules. Red dots represent 24 sites with impact proxies but lacking Pt measurements.]]

In 2019, Pino and others reported evidence in sediment layers with charcoal and pollen assemblages both indicating major disturbances at Pilauco Bajo, Chile in sediments dated to 12,800 BP.{{sfnp|Pino|Abarzúa|Astorga|Martel-Cea|2019}} This included rare metallic spherules, melt glass and nanodiamonds thought to have been produced during airbursts or impacts.{{sfnp|Pino|Abarzúa|Astorga|Martel-Cea|2019}} Pilauco Bajo is the southernmost site where evidence of the Younger Dryas impacts has been reported. This has been interpreted as evidence that a strewn field from the Younger Dryas impact event may have affected at least 30% of Earth's radius.{{sfnp|Pino|Abarzúa|Astorga|Martel-Cea|2019}} Also in 2019, CR Moore and others reported analysis of age-dated sediments from a long-lived pond in South Carolina showed not just an overabundance of platinum but a platinum/palladium ratio inconsistent with a terrestrial origin, as well as an overabundance of soot and a decrease in fungal spores associated with the dung of large herbivores, suggesting large-scale regional wildfires and at least a local decrease in ice age megafauna.{{Cite web|last=Moore |first=Christopher R. |name-list-style=vanc |date=October 22, 2019 |title=New evidence that an extraterrestrial collision 12,800 years ago triggered an abrupt climate change for Earth |url=https://theconversation.com/new-evidence-that-an-extraterrestrial-collision-12-800-years-ago-triggered-an-abrupt-climate-change-for-earth-118244 |url-status=live |archive-url=https://web.archive.org/web/20191023135255/http://theconversation.com/new-evidence-that-an-extraterrestrial-collision-12-800-years-ago-triggered-an-abrupt-climate-change-for-earth-118244 |archive-date=23 October 2019 |access-date=June 22, 2021 |website=The Conversation}}

In 2019, Thackery and others reported that a ~10 ppb platinum (Pt) enrichment in peat deposits at Wonderkrater in South Africa was associated with the YDB, although the age uncertainty range of the anomaly exceeded 2 thousand years.{{Cite Q |Q106978252 |author1-last=Thackeray |author1-first=J.F. |author2-last=Scott |author2-first=L. |author3-last=Pieterse |author3-first=P. |name-list-style=vanc}}

In 2019 research at White Pond near Elgin, South Carolina, conducted by CR Moore from the University of South Carolina and 16 colleagues, used a core to extract sediment samples from underneath the pond. The samples, dated by radiocarbon to the beginning of the Younger Dryas, were found to contain a large platinum anomaly, consistent with findings from other sites. A large soot anomaly was also found in cores from the site.{{Cite press release |title=UofSC archaeologist finds evidence of extinction theory |date=2019-10-22 |url=https://www.sc.edu/uofsc/posts/2019/10/10_chris_moore_research.php |last1=Ward |first1=Carol J.G. |name-list-style=vanc |access-date=2021-08-07 |url-status=live |archive-url=https://web.archive.org/web/20210303115411/https://www.sc.edu/uofsc/posts/2019/10/10_chris_moore_research.php |archive-date=2021-03-03 |publisher=University of South Carolina}}{{Cite journal |last1=Moore |first1=Christopher R. |last2=Brooks |first2=Mark J. |last3=Goodyear |first3=Albert C. |author-link3=Albert Goodyear |last4=Ferguson |first4=Terry A. |last5=Perrotti |first5=Angelina G. |last6=Mitra |first6=Siddhartha |last7=Listecki |first7=Ashlyn M. |last8=King |first8=Bailey C. |last9=Mallinson |first9=David J. |last10=Lane |first10=Chad S. |last11=Kapp |first11=Joshua D. |first12=Allen |last12=West |first13=David L. |last13=Carlson |first14=Wendy S. |last14=Wolbach |first15=Theodore R. |last15=Them II |first16=M. Scott |last16=Harris |first17=Sean |last17=Pyne-O’Donnell |display-authors=8 |name-list-style=vanc |date=22 October 2019 |title=Sediment Cores from White Pond, South Carolina, contain a Platinum Anomaly, Pyrogenic Carbon Peak, and Coprophilous Spore Decline at 12.8 ka |journal=Scientific Reports |volume=9 |bibcode=2019NatSR...915121M |doi=10.1038/s41598-019-51552-8 |pmc=6805854 |pmid=31641142 |doi-access=free |number=15121 (2019)|page=15121 }}

File:Abu Hureyra meltglass.png{{hair space}}{{Cite Q|Q90119243|last1=Moore|first1=Andrew M. T.|author-link1=Andrew M. T. Moore|last2=Kennett|first2=James P.|author-link2=James P. Kennett|last3=Napier|first3=William M.|author-link3=William Napier (astronomer)|last4=Bunch|first4=Ted E.|last5=Weaver|first5=James C.|last6=LeCompte|first6=Malcolm|last7=Adedeji|first7=A. Victor|last8=Hackley|first8=Paul|last9=Kletetschka|first9=Gunther|last10=Hermes|first10=Robert E.|last11=Wittke|first11=James H.|last12=Razink|first12=Joshua J.|last13=Gaultois|first13=Michael W.|last14=West|first14=Allen|display-authors=8|name-list-style=vanc|quote=The wide range of evidence supports the hypothesis that a cosmic event occurred at Abu Hureyra ~12,800 years ago, coeval with impacts that deposited high-temperature meltglass, melted microspherules, and/or platinum at other YDB sites on four continents.|date=Mar 6, 2020}}]]

In 2020, a group led by Allen West reported high concentrations of iridium, platinum, nickel, and cobalt at the Younger Dryas boundary in material from Tell Abu Hureyra. They concluded that the evidence supports the impact hypothesis,{{Cite press release |title=Fire from the Sky |date=2020-03-06 |url=https://www.news.ucsb.edu/2020/019823/fire-sky |quote=Based on materials collected before the site was flooded, Kennett and his colleagues contend Abu Hureyra is the first site to document the direct effects of a fragmented comet on a human settlement.|last1=Fernandez |first1=Sonia |name-list-style=vanc |access-date=2021-08-07 |url-status=live |archive-url=https://web.archive.org/web/20210706231340/https://www.news.ucsb.edu/2020/019823/fire-sky |archive-date=2021-07-06 |publisher=University of California, Santa Barbara}} but this was quickly contradicted by another study calling the YDIH into question because the samples were extremely unlikely to have been deposited at the same time.{{cite journal |display-authors=etal|last1=Hai Cheng |title=Timing and structure of the Younger Dryas event and its underlying climate dynamics |journal=PNAS |date=Sep 8, 2020 |volume=117 |issue=38 |pages=23408–23417 |doi=10.1073/pnas.2007869117 |doi-access=free |pmid=32900942 |pmc=7519346 |bibcode=2020PNAS..11723408C |hdl=10261/240073 |hdl-access=free }} Since all samples from the site were expended, the findings cannot be confirmed.{{cite journal |last1=Moore |first1=Andrew M. T. |author-link1=Andrew M. T. Moore |last2=Kennett |first2=James P. |author-link2=James P. Kennett |last3=Napier |first3=William M. |author-link3=William Napier (astronomer) |last4=Bunch |first4=Ted E. |last5=Weaver |first5=James C. |last6=LeCompte |first6=Malcolm |last7=Adedeji |first7=A. Victor |last8=Hackley |first8=Paul |last9=Kletetschka |first9=Gunther |last10=Hermes |first10=Robert E. |last11=Wittke |first11=James H. |last12=Razink |first12=Joshua J. |last13=Gaultois |first13=Michael W. |last14=West |first14=Allen |display-authors=8 |name-list-style=vanc |title= Evidence of cosmic impact at Abu Hureyra, Syria at theYounger Dryas Onset (~12.8 ka): High-temperature melting at >2200 °C |url= https://pubpeer.com/publications/CB9BF60F18A553088BEFB061164940 |access-date=2023-11-05 |website=PubPeer|date=6 March 2020 }}

In 2022, a paper by geologist James L. Powell, a YDIH proponent, claimed that opponents had prematurely rejected YDIH,{{Cite journal |last=Powell |first=James Lawrence |date=January 2022 |title=Premature rejection in science: The case of the Younger Dryas Impact Hypothesis |journal=Science Progress |language=en |volume=105 |issue=1 |pages=003685042110642 |doi=10.1177/00368504211064272 |issn=0036-8504 |pmc=10450282 |pmid=34986034}} detailing the example of research published by Firestone and others in 2001 and the inability of a later study by Surovell and others in 2009 that was unable to reproduce these results leading a number of other scientists to reject YDIH.{{Rp|location=Table 4}} Powell argues that since then, many independent studies have reproduced that evidence at dozens of YD sites.

A March 2023 article by planetary impact physicist Mark Boslough and YDIH opponent stated that "...the YDIH has never been accepted by experts in any related field" because it is "plagued by self contradictions, logical fallacies, basic misunderstandings, misidentified impact evidence, abandoned claims, irreproducible results, questionable protocols, lack of disclosure, secretiveness, failed predictions, contaminated samples, pseudoscientific arguments, physically impossible mechanisms, and misrepresentations".{{cite journal |last1=Boslough |first1=Mark |date=March 2023 |title=Apocalypse! Why Graham Hancock's use of the Younger Dryas impact hypothesis in his Netflix series Ancient Apocalypse is all wet|url=https://www.skeptic.com/reading_room/graham-hancocks-ancient-apocalypse-hypothesis-put-to-test/ |journal=Skeptic Magazine |volume=28 |issue=1 |pages=51–59}}

{{Self-reference cleanup|date=March 2024}}

In July 2023 Holliday and others published a comprehensive refutation of the YDIH that collected and summarized many of the positions from opponents to YDIH publications mentioned in the above history. Sections in this article refute the areas of evidence regarding Hypothetical impact markers,{{Rp|location=Sec. 8-12}} "Black mats,"{{Rp|location=Sec. 6}} Extinction of megafauna,{{Rp|location=Sec. 3.2}} Impact on human societies,{{Rp|location=Sec. 3.1}} the Hiawatha crater.{{Rp|location=Sec. 7}} Also criticized were fundamental assumptions,{{Rp|location=Sec. 3}} flawed sampling,{{Rp|location=Sec. 4}} inadequate dating,{{Rp|location=Sec. 5}} Pseudoarchaeological divined date of the impact event,{{Rp|location=Sec. 5.2}} pseudoscience (fringe) evidence and conjecture,{{Rp|location=Sec. 14}} issues with other YDIH claims, such as the Carolina bays,{{Rp|location=Sec. 13.1}} contradictory results when different groups have examined the same sample specimens,{{Rp|location=Sec. 14}} and unparalleled promotion of YDIH outside of scientific literature.{{Rp|location=Sec. 14}} The paper also responded to and critiqued assertions from Powell. The paper concludes that since "YDIH evolved directly from pseudoscience, the initial publication in scientific literature was seriously plagued by poorly documented interpretations and baseless assertions." and lists 11 serious flaws that persist in YDIH.{{Rp|location=Sec. 17}}

In a December 2023 article by CR Moore and others{{Cite journal |last1=Moore |first1=Christopher R. |last2=Brooks |first2=Mark J. |last3=Dunbar |first3=James S. |last4=Hemmings |first4=C. Andrew |last5=Langworthy |first5=Kurt A. |last6=West |first6=Allen |last7=LeCompte |first7=Malcolm A. |last8=Adedeji |first8=Victor |last9=Kennett |first9=James P. |last10=Feathers |first10=James K. |date=2023-12-20 |title=Platinum and microspherule peaks as chronostratigraphic markers for onset of the Younger Dryas at Wakulla Springs, Florida |journal=Scientific Reports |language=en |volume=13 |issue=1 |pages=22738 |doi=10.1038/s41598-023-50074-8 |issn=2045-2322 |pmc=10733423 |pmid=38123649|bibcode=2023NatSR..1322738M }} stated that "anomalous peak abundances of platinum and Fe-rich microspherules with high-temperature minerals have previously been demonstrated to be a chronostratigraphic marker for the lower Younger Dryas Boundary (YDB) dating to 12.8 ka," was found in sediments at Wakulla Springs, Florida. "The study confirms the utility of this YDB datum layer for intersequence correlation and for assessing relative ages of Paleoamerican artifacts, including those of likely Clovis, pre-Clovis, and post-Clovis age and their possible responses to environmental changes known to have occurred during the Younger Dryas cool climatic episode."

The impact hypothesis has been the subject of documentaries,{{Cite web |last=Balter |first=Michael |author-link=Michael Balter |name-list-style=vanc |date=2014-05-12 |title=What Caused a 1300-Year Deep Freeze? |url=https://www.science.org/content/article/what-caused-1300-year-deep-freeze |url-status=live |archive-url=https://web.archive.org/web/20220425133559/https://www.science.org/content/article/what-caused-1300-year-deep-freeze |archive-date=2022-04-25 |access-date=2021-08-21 |website=Science |quote=The notion was popularized in television documentaries and other coverage on the National Geographic Channel, History Channel, and the PBS program NOVA.}} including Mammoth Mystery on National Geographic Explorer (2007),{{Cite web |date=2007-10-07 |title=Mammoth Mystery |url=https://www.imdb.com/title/tt1118275/ |access-date=2021-08-20 |website=IMDb}} Journey to 10,000 BC on the History Channel (2008),{{Cite web |date=2008 |title=Journey to 10,000 BC |url=https://www.imdb.com/title/tt1203519/ |access-date=2021-08-20 |website=IMDb}} Survival Earth on Channel 4 (2008), and Megabeasts' Sudden Death on PBS Nova (2009).{{efn|Megabeasts Sudden Death was removed from online streaming after NOVA WGBH learned about problems with the hypothesis and data discrancies.}}{{cite AV media |url= https://m.youtube.com/watch?v=e6APBjExE0E |website=YouTube|title= Megabeasts Sudden Death, PBS NOVA 2009|year=2022}}{{Cite web |date=2009-03-31 |title=Megabeasts' Sudden Death |url=https://www.imdb.com/title/tt1393568/ |access-date=2021-08-20 |website=IMDb}}{{Cite web |date=2009-03-31 |title=Megabeasts' Sudden Death |url=https://www.pbs.org/wgbh/nova/evolution/last-extinction.html |url-status=live |archive-url=https://web.archive.org/web/20210612071305/https://www.pbs.org/wgbh/nova/evolution/last-extinction.html |archive-date=2021-06-12 |access-date=2021-08-20 |website=PBS Nova}}

Graham Hancock argued in his 2015 book Magicians of the Gods that the Younger Dryas comet destroyed the earth in a time cycle and that it was responsible for the Noahide flood myth. He inferred that this myth was widespread elsewhere on earth by comparing it with the flood mythology of other peoples.{{Cite web |last=Taube |first=Michael |name-list-style=vanc |date=December 30, 2015 |title=Book Review - Magicians of the Gods |url=https://www.washingtontimes.com/news/2015/dec/30/book-review-magicians-of-the-gods/ |url-status=live |archive-url=https://web.archive.org/web/20210120225320/https://www.washingtontimes.com/news/2015/dec/30/book-review-magicians-of-the-gods/ |archive-date=20 January 2021 |access-date=14 January 2021 |website=The Washington Times}}{{Cite web |date=2015-09-03 |title=MAGICIANS OF THE GODS by Graham Hancock |url=https://www.kirkusreviews.com/book-reviews/graham-hancock/magicians-of-the-gods/ |url-status=live |archive-url=https://web.archive.org/web/20210120231351/https://www.kirkusreviews.com/book-reviews/graham-hancock/magicians-of-the-gods/ |archive-date=20 January 2021 |access-date=14 January 2021 |website=Kirkus Reviews}} These claims were criticized as inaccurate by independent reviewers, including Jason Colavito, Michael Shermer, and Marc J. Defant.{{efn|name=POV}}{{Cite web |last=Colavito |first=Jason |author-link=Jason Colavito |name-list-style=vanc |title=Magicians of the Gods Review |url=http://www.jasoncolavito.com/magicians-of-the-gods-review.html |url-status=live |archive-url=https://web.archive.org/web/20201205051354/http://www.jasoncolavito.com/magicians-of-the-gods-review.html |archive-date=5 December 2020 |access-date=2017-11-16 |website=Jason Colavito}}{{Cite news |last=Shermer |first=Michael |author-link=Michael Shermer |name-list-style=vanc |date=1 June 2017 |title=No, There Wasn't an Advanced Civilization 12,000 Years Ago |publisher=Scientific American |url=https://www.scientificamerican.com/article/no-there-wasnt-an-advanced-civilization-12-000-years-ago/ |url-status=live |access-date=28 April 2022 |archive-url=https://web.archive.org/web/20220220132025/https://www.scientificamerican.com/article/no-there-wasnt-an-advanced-civilization-12-000-years-ago/ |archive-date=2022-02-20}}{{Cite web |last=Defant |first=Marc J. |name-list-style=vanc |date=September 1, 2017 |title=Conjuring Up a Lost Civilization: An Analysis of the Claims Made by Graham Hancock in Magicians of the Gods |url=https://www.skeptic.com/reading_room/defant-analysis-of-hancock-claims-in-magicians-of-the-gods/ |url-status=live |archive-url=https://web.archive.org/web/20210427141018/https://www.skeptic.com/reading_room/defant-analysis-of-hancock-claims-in-magicians-of-the-gods/ |archive-date=27 April 2021 |access-date=27 April 2021 |website=Skeptic magazine}} Hancock expanded on his claims in a subsequent book, America Before: The Key to Earth's Lost Civilization (2019), in which he claimed that the Younger Dryas catastrophe had wiped out all traces of a sophisticated Ice Age civilization in North America.{{Cite news |last=Casci |first=Mark |name-list-style=vanc |date=2019-03-29 |title=Fresh clues in the hunt for a lost civilization - Graham Hancock interview |work=The Yorkshire Post |url=https://www.yorkshirepost.co.uk/whats-on/arts-and-entertainment/fresh-clues-hunt-lost-civilization-graham-hancock-interview-1757617 |url-status=live |access-date=2022-04-29 |archive-url=https://web.archive.org/web/20220109140107/https://www.yorkshirepost.co.uk/whats-on/arts-and-entertainment/fresh-clues-hunt-lost-civilization-graham-hancock-interview-1757617 |archive-date=2022-01-09}}

In 2017, a debate was held on the Joe Rogan Experience between proponents{{Clarify|date=December 2022|reason=Are these all proponents of Hancock's Noah's Flood idea, or just of the impact hypothesis?}} Graham Hancock, Randall Carlson, and Malcolm A. LeCompte and opponents Michael Shermer and Marc J. Defant.{{efn|name=POV|Both Michael Shermer and Marc J. Defant have since indicated that they accept the impact hypothesis.{{Cite tweet |user=michaelshermer |author=Michael Shermer |author-link=Michael Shermer |number=1237559469967421440 |title=Ok @Graham__Hancock I shall adjust my priors in light of more research like this, and modify my credence about your theory... 'Evidence of Cosmic Impact at Abu Hureyra, Syria at the Younger Dryas Onset (~12.8 ka): High-temperature melting at >2200 °C' https://doi.org/10.1038/s41598-020-60867-w}}{{Cite web |last=Defant |first=Marc J. |name-list-style=vanc |date=2020-06-05 |title=The Younger Dryas Impact Hypothesis |url=https://www.marcdefant.com/2020/06/05/the-younger-dryas-impact-hypothesis/ |url-status=live |archive-url=https://web.archive.org/web/20210126095442/https://www.marcdefant.com/2020/06/05/the-younger-dryas-impact-hypothesis/ |archive-date=2021-01-26 |access-date=2021-06-06 |quote=[Deadly Voyager] is a superb book and has absolutely convinced me there were comet airbursts at the Younger Dryas.}}}}{{Cite AV media |url=https://www.youtube.com/watch?v=tFlAFo78xoQ |archive-url=https://ghostarchive.org/varchive/youtube/20211221/tFlAFo78xoQ |archive-date=2021-12-21 |url-status=live |title=Joe Rogan Experience #961 - Graham Hancock, Randall Carlson & Michael Shermer |date=May 16, 2017 |last1=Rogan |first1=Joe |author-link1=Joe Rogan |last2=Hancock |first2=Graham |author-link2=Graham Hancock |last3=Carlson |first3=Randall |last4=Shermer |first4=Michael |author-link4=Michael Shermer |last5=Defant |first5=Marc J. |last6=LeCompte |first6=Malcolm A |name-list-style=vanc |time=2:06:55 |publisher=Joe Rogan Experience}}{{cbignore}} The week that the podcast was released, the network was reportedly averaging over 120 million downloads a month.{{Cite web |last=Shermer |first=Michael |author-link=Michael Shermer |name-list-style=vanc |title=Debating Science and Lost Civilizations |url=https://www.skeptic.com/reading_room/debating-science-lost-civilizations-shermer-experience-on-joe-rogan-961/ |url-status=live |archive-url=https://web.archive.org/web/20210629202546/https://www.skeptic.com/reading_room/debating-science-lost-civilizations-shermer-experience-on-joe-rogan-961/ |archive-date=2021-06-29 |access-date=2021-08-20 |website=Skeptic |date=23 April 2019 |quote=According to Joe, as of that week he was averaging over 120 million downloads a month, putting him on a par with the biggest talk show hosts on television, either cable or broadcast.}}

A 2021 episode of the Science Channel series Ancient Unexplained Files had a segment on the evidence from Abu Hureyra; geoscientist Sian Proctor also described the impact hypothesis as a whole.{{Cite episode |title=Gladiator Graveyard |url=https://www.facebook.com/ScienceChannel/videos/abu-hurayrah-ancient-unexplained-files/187455772937732/ |archive-url=https://ghostarchive.org/varchive/youtube/20211221/55Qa2MhUD9Y |archive-date=2021-12-21 |url-status=live|series=Ancient Unexplained Files |date=March 22, 2021 |season=1 |number=6 |time=12:40 |last1=Bellinger |first1=Karen |last2=Szulgit |first2=Greg |last3=Wright |first3=Jacob L. |author-link3=Jacob L. Wright |last4=Proctor |first4=Sian |author-link4=Sian Proctor |name-list-style=vanc |publisher=Science Channel}}{{cbignore}} Wikidata Q109762970.

In 2022 Graham Hancock presented in a Netflix series titled Ancient Apocalypse, with episode 8 specifically covering the YDIH. In March 2023 Mark Boslough published a commentary in Skeptic magazine with the conclusion that many attributes of the series are pseudoscience.

• {{annotated link|Carolina bays}}
• {{annotated link|Murray Springs Clovis Site}}
• {{annotated link|Shiva hypothesis}}
• {{annotated link|Taurids}}
• {{annotated link|Tollmann's bolide hypothesis}}
• Tunguska event and Chelyabinsk meteor - two examples of meteors exploding in the atmosphere

{{notelist|50em}}

{{Reflist|2}}

{{sfn whitelist|CITEREFPowell2022}}

{{refbegin}}

• {{Cite journal |last1=Pino |first1=Mario |author-link=Mario Pino Quivira |last2=Abarzúa |first2=Ana M. |last3=Astorga |first3=Giselle |last4=Martel-Cea |first4=Alejandra |last5=Cossio-Montecinos |first5=Nathalie |last6=Navarro |first6=R. Ximena |last7=Lira |first7=Maria Paz |last8=Labarca |first8=Rafael |last9=LeCompte |first9=Malcolm A. |last10=Adedeji |first10=Victor |last11=Moore |first11=Christopher R. |last12=Bunch |first12=Ted E. |last13=Mooney |first13=Charles |last14=Wolbach |first14=Wendy S. |last15=West |first15=Allen |last16=Kennett |first16=James P. |author-link16=James P. Kennett |display-authors=8 |name-list-style=vanc |date=13 March 2019 |title=Sedimentary record from Patagonia, southern Chile supports cosmic-impact triggering of biomass burning, climate change, and megafaunal extinctions at 12.8 ka |journal=Scientific Reports |volume=9 |issue=1 |pages=4413 |bibcode=2019NatSR...9.4413P |doi=10.1038/s41598-018-38089-y |pmc=6416299 |pmid=30867437}}
• {{Cite Q |Q110444998 |last=Powell |first=James Lawrence |author-link=James L. Powell |name-list-style=vanc}}
• {{Cite journal |last1=Sun |first1=N. |last2=Brandon |first2=A. D. |last3=Forman |first3=S. L. |last4=Waters |first4=M. R. |author-link4=Michael R. Waters |last5=Befus |first5=K. S. |name-list-style=vanc |date=1 July 2020 |title=Volcanic origin for Younger Dryas geochemical anomalies ca. 12,900 cal B.P. |journal=Science Advances |volume=6 |issue=31 |pages=eaax8587 |bibcode=2020SciA....6.8587S |doi=10.1126/sciadv.aax8587 |issn=2375-2548 |pmc=7399481 |pmid=32789166}}

{{refend}}

{{refbegin}}

• {{Cite news |last=Bentley |first=Molly |name-list-style=vanc |date=2009-01-02 |title=Diamond clues to beasts' demise |work=BBC News |url=http://news.bbc.co.uk/2/hi/science/nature/7808171.stm |url-status=live |access-date=15 April 2012 |archive-url=https://web.archive.org/web/20100903164436/http://news.bbc.co.uk/2/hi/science/nature/7808171.stm |archive-date=3 September 2010}}
• {{Cite web |last=Bressan |first=David |name-list-style=vanc |date=27 July 2011 |title=The Younger Dryas Impact Hypothesis |url=http://blogs.scientificamerican.com/history-of-geology/2011/07/27/the-younger-dryas-impact-hypothesis/ |url-status=live |archive-url=https://web.archive.org/web/20130315103904/http://blogs.scientificamerican.com/history-of-geology/2011/07/27/the-younger-dryas-impact-hypothesis/ |archive-date=15 March 2013 |access-date=15 April 2012 |publisher=Scientific American Blog Network}}
• {{Cite web |last=Fernandez |first=Sonia |name-list-style=vanc |date=May 21, 2013 |title=Comprehensive Analysis of Impact Spherules Supports Theory of Cosmic Impact 12,800 Years Ago |url=https://www.news.ucsb.edu/2013/013537/comprehensive-analysis-impact-spherules-supports-theory-cosmic-impact-12800-years-ago |url-status=live |archive-url=https://web.archive.org/web/20210216003210/https://www.news.ucsb.edu/2013/013537/comprehensive-analysis-impact-spherules-supports-theory-cosmic-impact-12800-years-ago |archive-date=2021-02-16 |access-date=2021-06-24 |publisher=UC Santa Barbara}}
• {{Cite news |last=Firestone |first=Richard B. |name-list-style=vanc |date=24 July 2019 |title=Disappearance of Ice Age Megafauna and the Younger Dryas Impact |work=Capeia |url=https://beta.capeia.com/planetary-science/2019/06/03/disappearance-of-ice-age-megafauna-and-the-younger-dryas-impact |url-status=live |access-date=2021-06-30 |archive-url=https://web.archive.org/web/20210410041144/https://beta.capeia.com/planetary-science/2019/06/03/disappearance-of-ice-age-megafauna-and-the-younger-dryas-impact |archive-date=2021-04-10}}
• {{Cite web |last=Hoffman |first=Carey |name-list-style=vanc |date=2 July 2008 |title=Exploding Asteroid Theory Strengthened by New Evidence Located in Ohio, Indiana |url=http://www.uc.edu/news/NR.asp?id=8625 |url-status=live |archive-url=https://web.archive.org/web/20080731170933/http://www.uc.edu/news/NR.asp?id=8625 |archive-date=31 July 2008 |access-date=5 August 2008 |publisher=University of Cincinnati}}
• {{Cite web |author-link=Vance T. Holliday |year=2011 |title=A Cosmic Catastrophe: The Great Clovis Comet Debate: A personal perspective on an Outrageous Hypothesis |url=http://www.argonaut.arizona.edu/Clovis_Comet_Debate.html |url-status=dead |archive-url=https://web.archive.org/web/20160305031317/http://www.argonaut.arizona.edu/Clovis_Comet_Debate.html |archive-date=5 March 2016 |access-date=14 July 2011 |website=Argonaut Archaeological Research Fund |publisher=Department of Anthropology at the University of Arizona, University of Arizona |location=Tucson, Arizona |vauthors=Holliday VT}}
• {{Cite journal |last=Pringle |first=Heather |author-link=Heather Pringle (writer) |name-list-style=vanc |date=23 May 2007 |title=Firestorm from space wiped out prehistoric Americans |url=https://www.newscientist.com/article/mg19426052.900 |url-status=live |journal=New Scientist |volume=194 |issue=2605 |pages=8–9 |doi=10.1016/S0262-4079(07)61277-9 |archive-url=https://web.archive.org/web/20120914152028/http://www.newscientist.com/article/mg19426052.900 |archive-date=14 September 2012 |access-date=19 September 2017}}
• {{cite journal |first=Martin B. |last=Sweatman |title=The Younger Dryas impact hypothesis: Review of the impact evidence |journal=Earth-Science Reviews |volume=218 |date=July 2021 |page=103677 |issn=0012-8252 |doi=10.1016/j.earscirev.2021.103677 |bibcode=2021ESRv..21803677S |s2cid=236231169 |url=https://www.pure.ed.ac.uk/ws/files/209288439/The_Younger_Dryas_impact_hypothesis_MBS.pdf }}

;Presentations of the American Geophysical Union

• {{Cite web |date=2009-12-16 |title=Younger Dryas Boundary: Extraterrestrial Impact or Not II |url=http://www.georgehoward.net/ORAL%20Younger%20Dryas%20Boundary%20Extraterrestrial%20Impact%20or%20Not%20FALL%20AGU.pdf |url-status=dead |archive-url=https://web.archive.org/web/20120206151647/http://www.georgehoward.net/ORAL%20Younger%20Dryas%20Boundary%20Extraterrestrial%20Impact%20or%20Not%20FALL%20AGU.pdf |archive-date=6 February 2012 |access-date=15 April 2012 |location=American Geophysical Union Fall Meeting, San Francisco, California}}
• {{Cite web |date=2009-12-16 |title=Younger Dryas Boundary: Extraterrestrial Impact or Not I |url=http://www.georgehoward.net/POSTER%20Younger%20Dryas%20Boundary%20Extraterrestrial%20Impact%20or%20Not%20FALL%20AGU.pdf |url-status=dead |archive-url=https://web.archive.org/web/20200423030516/http://www.georgehoward.net/POSTER%20Younger%20Dryas%20Boundary%20Extraterrestrial%20Impact%20or%20Not%20FALL%20AGU.pdf |archive-date=23 April 2020 |access-date=24 June 2021 |location=American Geophysical Union Fall Meeting, San Francisco, California}}

;Mammoth Trumpet

An extensive series of articles was published in [https://liberalarts.tamu.edu/csfa/publications-archives/mammoth-trumpet-archives/ Mammoth Trumpet], the magazine for Texas A&M University's Center for the Study of the First Americans, featuring conversations with many {{abbr|YDIH|Younger Dryas impact hypothesis}} proponents and opponents:

• {{Cite Q |Q107225241 |last=Largent |first=Floyd |name-list-style=vanc |title=The Clovis Comet - Part I: Evidence for a Cosmic Collision 12,900 Years Ago}}
• {{Cite Q |Q107226201 |last=Largent |first=Floyd |name-list-style=vanc |title=The Clovis Comet - Part II: What the Data Tell Us}}
• {{Cite Q |Q107226305 |last=Largent |first=Floyd |name-list-style=vanc |title=The Clovis Comet - Part III: The Implications}}
• {{Cite Q |Q107226371 |last=Largent |first=Floyd |name-list-style=vanc |title=The Clovis Comet - Part IV: The Scientific Community Responds}}
• {{Cite Q |Q107228406 |last=Lepper |first=Bradley |name-list-style=vanc |title=Fire Record Undercuts Clovis Comet Theory}}
• {{Cite Q |Q107228547 |last=Largent |first=Floyd |name-list-style=vanc |title=The Clovis Comet Revisited - In the Crucible of Scientific Inquiry}}
• {{Cite Q |Q107228612 |last=Largent |first=Floyd |name-list-style=vanc |title=The Clovis Comet Revisited - The Nanodiamond Controversy, Part I}}
• {{Cite Q |Q107228963 |last=Largent |first=Floyd |name-list-style=vanc |title=The Clovis Comet Revisited - The Nanodiamond Controversy, Part II: A Case of Mistaken Identity?}}
• {{Cite Q |Q107229168 |last=Largent |first=Floyd |name-list-style=vanc |title=The Clovis Comet - The Cratering Evidence}}
• {{Cite Q |Q107229501 |last=Largent |first=Floyd |name-list-style=vanc |title=The Clovis Comet - New Developments in the Proxy Evidence, Part I}}
• {{Cite Q |Q107230043 |last=Largent |first=Floyd |name-list-style=vanc |title=The Clovis Comet - New Developments in the Proxy Evidence, Part II}}
• {{Cite Q |Q107230085 |last=Largent |first=Floyd |name-list-style=vanc |title=The Clovis Comet - New Developments in the Proxy Evidence, Part III}}

{{refend}}

{{Scholia}}

• {{Commons category-inline}}

{{DEFAULTSORT:Younger Dryas Event}}

Younger Dryas impact hypothesis

Category:Hypothetical impact events

Category:Ecological theories

Category:Extinction events