Younger Dryas impact hypothesis
The Younger Dryas impact hypothesis or Clovis comet hypothesis posits that fragments of a large (more than 4 kilometers in diameter), disintegrating asteroid or comet struck North America, South America, Europe, and western Asia about 12,800 years ago. Multiple airbursts/impacts produced the Younger Dryas (YD) boundary layer (YDB), depositing peak concentrations of platinum, high-temperature spherules, meltglass, and nanodiamonds, forming an isochronous datum at more than 50 sites across about 50 million km² of Earth’s surface. Some scientists have proposed that this event triggered extensive biomass burning, a brief impact winter, the Younger Dryas abrupt climate change, contributed to extinctions of late Pleistocene megafauna, and resulted in the end of the Clovis culture.
- 1 Evidence
- 2 Consequences of such an impact
- 3 History of the hypothesis
- 4 Criticism
- 4.1 Criticism of chronology and age-dating
- 4.2 Disputed origin and occurrence of physical evidence
- 5 In popular culture
- 6 See also
- 7 References
- 8 Further reading
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 dozens of Clovis culture archaeological sites in North America. Proponents have reported materials including nanodiamonds, metallic microspherules, carbon spherules, magnetic spherules, iridium, platinum, 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.. Proponents of the hypothesis claim that these data cannot be adequately explained by volcanic, anthropogenic, or other natural processes.
Consequences of such an impact
It is hypothesized that this impact event brought about the extinction of many species of North American Pleistocene megafauna. These animals included camels, mammoths, the giant short-faced bear, and numerous other species that the proponents suggest died out at this time. The proposed markers for the impact event are claimed to have contributed to the transition from Clovis culture to subsequent patterns. This supposed event is claimed to have triggered extensive biomass burning, a brief impact winter, and an abrupt climate change.
History of the hypothesis
The original hypotheses about a comet impact that had a widespread effect on human populations can be attributed to Edmund Halley, who in 1694 suggested that a worldwide flood had been the result of a near-miss by a comet. The issue was taken up in more detail by William Whiston, a protegé of and popularizer of the theories of Isaac Newton, who argued in his book A New Theory of the Earth (1696) that a comet impact was the probable cause of the Biblical Flood of Noah. Whiston also attributed the origins of the atmosphere and other significant changes in the Earth to the effects of comets.
This hypothesis was subsequently popularized by Minnesota congressman and pseudoarchaeology writer Ignatius L. Donnelly in his book Ragnarok: The Age of Fire and Gravel (1883), which followed his better-known book Atlantis: The Antediluvian World (1882). In Ragnarok, Donnelly argued that an enormous comet struck the earth approximately 12,000 years ago, destroying an advanced civilization on the "lost continent" of Atlantis. Donnelly, following Halley and Whiston, attributed the Biblical Flood to this event, which he hypothesized had also resulted in catastrophic fires and significant climate change. Shortly after the publication of Ragnarok, one commenter noted, "Whiston ascertained that the deluge of Noah came from a comet's tail; but Donnelly has outdone Whiston, for he has shown that our planet has suffered not only from a cometary flood, but from cometary fire, and a cometary rain of stones."
21st century revival and refinement
In 2006, this hypothesis was revived in 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 published by Inner Traditions - Bear & Company and marketed in the category of Earth Changes, a phrase coined by psychic Edgar Cayce. It proposed that a large air burst or earth impact of one or more comets initiated the Younger Dryas cold period about 12,900 BP calibrated (10,900 14C uncalibrated) years ago.
In 2007, Firestone, West, and twenty-four other authors suggested that the impact event may have led to an immediate decline in human populations in North America at that time.
In 2008, C. Vance Haynes Jr. published data to support the synchronous nature of the black mats, 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 B.P. (14C uncalibrated) that we have yet to understand." The first debate between proponents and skeptics was held at the 2008 Pecos Conference in Flagstaff, Arizona. http://www.swanet.org/2008_pecos_conference/related.html
In 2009, a paper in the Proceedings of the National Academy of Sciences offered evidence of impact glass that resulted from the impact of a meteorite. Another asserted that a swarm of carbonaceous chondrites or comet fragments from air burst(s) or impact(s) 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. Another article in Science reported evidence of nanodiamonds in a geological deposit thought to correspond to the event. In the same issue, another article reported that the nanodiamonds were evidence for carbonaceous chondrites or comets at the start of Younger Dryas whose airbursts and surface impacts caused widespread damage. A special debate-style session was convened at the 2009 AGU Fall Meeting in which skeptics and supporters alternated in giving presentations. http://abstractsearch.agu.org/meetings/2009/FM/PP31D.html http://abstractsearch.agu.org/meetings/2009/FM/PP33B.html
In 2010 the American Quaternary Association held a debate between skeptics and supporters in Laramie, Wyoming. https://cosmictusk.com/shootout-ydb-hypothesis-at-laramie-amqua-conference
In 2011, a large group of scientists challenged the Younger Dryas impact hypothesis on the basis of claims that most of the conclusions could not be reproduced and were a misinterpretation of data. The article claimed that no nanodiamonds were found and that the supposed carbon spherules could be fungus or insect feces and included modern contaminants. In response, in June 2013 some of the original proponents published a re-evaluation of spherules from eighteen sites worldwide that they interpret as supporting their hypothesis. Skepticism increased with the revelation of documentation demonstrating misconduct and past criminal conduct (conviction for fraud and misrepresentation of credentials by one of the lead authors of the original publications, Allen West, who later convinced a judge to void the old plea after his colleagues found out). 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.
In 2012, scientists reported evidence supporting a modified version of the Younger Dryas impact hypothesis—involving a much smaller, non-cometary impactor—was found in lake bed cores dating to 12,900 BP 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. The results of the study have not been replicated by other researchers. Lonsdaleite has also been made artificially in laboratories.
In 2013, scientists reported a hundredfold spike in the concentration of platinum in Greenland ice cores that are dated to 12,890 BP with 5-year accuracy. The authors of that study conclude that such a small impact of an iron meteorite is “unlikely to result in an airburst or trigger wide wildfires proposed by the YDB impact hypothesis." But they write that the large Pt anomaly "hints for an extraterrestrial source of Pt," showing that any disagreement with the proponents of the original YDIH is over the nature of the extraterrestrial object, not whether there was one, and it is much more likely that the Greenland Pt anomaly was caused by a small local iron meteorite fall without any widespread consequences.
In 2016, a report on further analysis of Younger Dryas boundary sediments at nine sites found no evidence of an extraterrestrial impact at the Younger Dryas boundary. Also that year, an analysis of nanodiamond evidence failed to uncover lonsdaleite or a spike in nanodiamond concentration at the YDB. Radiocarbon dating, microscopy of paleobotanical samples, and analytical pyrolysis of fluvial sediments "[found] no evidence in Arlington Canyon for an extraterrestrial impact or catastrophic impact-induced fire." Exposed fluvial sequences in Arlington Canyon on Santa Rosa Island "features centrally in the controversial hypothesis of an extra-terrestrial impact at the onset of the Younger Dryas." The nanodiamond evidence was criticized further in 2017.
In 2017, scientists reported a Pt anomaly dating at eleven continental sites dated to the Younger Dryas.
In 2018, some researchers interpreted the undated Hiawatha Glacier impact crater in Greenland as evidence for the Younger Dryas impact event due to its location. Two papers were published dealing with an "extraordinary biomass-burning episode" associated with the Younger Dryas Impact.
In 2019, scientists 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. This included rare metallic spherules, melt glass and nanodiamonds thought to have been produced during airbursts or impacts. 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.
In 2019, a South African team consisting of Francis Thackeray, Louis Scott and Philip Pieterse announced the discovery of a platinum (Pt) spike in peat deposits at Wonderkrater, an artesian spring site in South Africa in the Limpopo Province, near the town of Mookgophong (formerly Naboomspruit) situated between Pretoria and Polokwane http://wiredspace.wits.ac.za/handle/10539/28129. The spike in platinum was documented in a sample dated at 12,744 cal years BP, preceding a decline in a paleo-temperature index based on multivariate analysis of pollen spectra. This drop in temperature is associated with the Younger Dryas. The Wonderkrater platinum spike is in marked contrast to the almost constant low Pt concentrations in adjacent levels. It is consistent with the Younger Dryas Impact Hypothesis and is the first of its kind in Africa, supplementing evidence for platinum anomalies at more than 25 other sites in the world. The platinum spike at the South African site has been interpreted in terms of global dispersal of platinum-rich dust at the time of the hypothesized asteroid impact, potentially associated with a crater of the kind found beneath the Hiawatha Glacier in Greenland. Thackeray and his colleagues recognise that Terminal Pleistocene megafaunal extinctions in southern Africa (Megalotragus priscus, Syncerus antiquus and Equus capensis) may be attributed to both environmental change and human predation within a period of time before and after 12,800 cal yr BP. However, on the basis of data presented in their study, they state that the consequences of a hypothesised YD cosmic impact (including the dispersal of atmospheric dust) may have contributed to some extent to the process of extinctions not only in southern Africa, but also to that which occurred in North and South America as well as Europe, recognising synchroneity of Pt anomalies that has been cited in support the Younger Dryas Impact Hypothesis. It is noted that in parts of South Africa, the Robberg stone tool technology terminates at about 12,800 cal yr BP, co-terminus with the termination of the Clovis technocomplex in North America, but further work is required to assess this coincidence.
Criticism of chronology and age-dating
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. They suggested that the hypothesis would probably need to be revised. There is also no evidence of continent-wide wildfires at any time during terminal Pleistocene deglaciation, though there is evidence that most larger wildfires had a human origin, which calls into question the origin of the "black mat." Iridium, magnetic minerals, microspherules, carbon, and nanodiamonds are all subject to differing interpretations as to their nature and origin, and may be explained in many cases by purely terrestrial or non-catastrophic factors.
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. 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, and the survival of ground sloths in the Antilles, the Caribbean, until 4700 cal BP. The Australian megafaunal extinctions occurred approximately 30,000 years earlier than the hypothetical Younger Dryas event.
The megafaunal extinction pattern observed in North America poses a problem for the bolide impact scenario, since it raises the question why large mammals should be preferentially exterminated over small mammals or other vertebrates. 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 collapse in North American megafaunal population from 14,800 to 13,700 BP, well before the date of the hypothetical extraterrestrial impact, possibly from anthropogenic activities, including hunting.
Other research has shown no support for the impact hypothesis. One group 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.
Disputed origin and occurrence of physical evidence
Claims for carbon spherules, nanodiamonds, magnetic particles, and extraterrestrial platinum
Scientists have asserted that the carbon spherules originated as fungal structures and/or insect fecal pellets, and contained modern contaminants and that the claimed nanodiamonds are actually misidentified graphene and graphene/graphane oxide aggregates. An analysis of a similar Younger Dryas boundary layer in Belgium yielded carbon crystalline structures such as nanodiamonds, but the authors concluded that they also did not show unique evidence for a bolide impact. Researchers have also found no extraterrestrial platinum group metals in the boundary layer, which is inconsistent with the hypothesized impact event. Further independent analysis was unable to confirm prior claims of magnetic particles and microspherules, concluding that there was no evidence for a Younger Dryas impact event.
Evidence for widespread fires
Analysis of fluvial sediments on Santa Rosa Island by another group also found no evidence of lonsdaleite, impact-induced fires, or extraterrestrial impact. Research published in 2012 has shown that the so-called "black mats" are easily explained by typical earth processes in wetland environments. The 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, suggests that these markers arise from processes common to wetland systems, and probably not as a result of catastrophic bolide impacts.
Researchers have also criticized the conclusions of various studies for incorrect age-dating of the sediments, contamination by modern carbon, inconsistent hypothesis that made it difficult to predict the type and size of bolide, lack of proper identification of lonsdaleite, confusing an extraterrestrial impact with other causes such as fire, and for inconsistent use of the carbon spherule "proxy". Naturally occurring lonsdaleite has also been identified in non-bolide diamond placer deposits in the Sakha Republic.
Reproducibility of results
Proponents of the hypothesis have responded to defend their findings, disputing the accusation of irreproducibility or replicating their findings.[excessive citations]:Details should be specified and individually cited Critics of the hypothesis have repeatedly addressed the responses, and have published counterarguments.[excessive citations]
Supposed impact crater in Greenland
Even though a 2018 paper that presented evidence for an impact crater of unknown age under the Hiawatha Glacier in Greenland did not suggest any connection to the Younger Dryas, some scientists speculated without evidence about such a link in news reports. Skeptics reject this connection because it would require an improbably recent impact — an impact of this size should occur only once every few million years — and it would leave evidence, such as a young ejecta blanket. Moreover, this has not yet been accepted as a confirmed impact crater. Christian Koeberl, an impact crater expert from the University of Vienna, was quoted in Popular Science saying: “The authors report on some interesting phenomena, but the ‘definitive’ interpretation and conclusion that a large impact crater underneath the ice has been discovered is a severe over-interpretation of the existing data.”
In popular culture
In 1995, pseudoarchaeology author Graham Hancock, citing the work of Charles Hapgood and Rand Flem-Ath on the cataclysmic pole shift hypothesis, suggested in his book Fingerprints of the Gods that a major meteorite impact event in the Late Pleistocene had caused the Earth to shift so dramatically on its poles that a "lost civilization" on Antarctica had been shifted to the South Pole and was buried deep beneath the southern polar ice cap. Flem-Ath had previously suggested that this civilization was Atlantis.
In 2015, in his book Magicians of the Gods: The Forgotten Wisdom of Earth's Lost Civilisation, Hancock suggested that the Younger Dryas impact event had destroyed a "lost civilization" whose remains included the archaeological site of Göbekli Tepe in Turkey, which dates to the Pre-Pottery Neolithic A period.
In 2019, Hancock prominently featured the Younger Dryas impact hypothesis in his book America Before: The Key to Earth's Lost Civilization, in which he claims that there was a direct meteorite impact on the center of a "lost civilization" of the Late Pleistocene, destroying virtually all traces of its existence. Joe Rogan interviewed Hancock in a podcast of The Joe Rogan Experience on April 22, 2019.
- Holocene extinction event
- Murray Springs Clovis Site
- Pleistocene megafauna
- Tollmann's bolide hypothesis
- Tunguska event
- Pino, Mario; Abarzúa, Ana M.; Astorga, Giselle; Martel-Cea, Alejandra; Cossio-Montecinos, Nathalie; Navarro, R. Ximena; Lira, Maria Paz; Labarca, Rafael; LeCompte, Malcolm A.; Adedeji, Victor; Moore, Christopher R.; Bunch, Ted E.; Mooney, Charles; Wolbach, Wendy S.; West, Allen; Kennett, James P. (13 March 2019). "Sedimentary record from Patagonia, southern Chile supports cosmic-impact triggering of biomass burning, climate change, and megafaunal extinctions at 12.8 ka". Scientific Reports. 9 (1): 4413. Bibcode:2019NatSR...9.4413P. doi:10.1038/s41598-018-38089-y. PMC 6416299. PMID 30867437.
- Dalton R (2007). "Blast in the past?". Nature. 447 (7142): 256–257. doi:10.1038/447256a. PMID 17507957.
- Wittke JH, Weaver JC, Bunch TE, Kennett JP, Kennett DJ, Moore AM, et al. (June 2013). "Evidence for deposition of 10 million tonnes of impact spherules across four continents 12,800 y ago". Proceedings of the National Academy of Sciences of the United States of America. 110 (23): E2088–97. Bibcode:2013PNAS..110E2088W. doi:10.1073/pnas.1301760110. PMC 3677428. PMID 23690611.
- Bunch TE, Hermes RE, Moore AM, Kennett DJ, Weaver JC, Wittke JH, et al. (July 2012). "Very high-temperature impact melt products as evidence for cosmic airbursts and impacts 12,900 years ago". Proceedings of the National Academy of Sciences of the United States of America. 109 (28): E1903–12. Bibcode:2012PNAS..109E1903B. doi:10.1073/pnas.1204453109. PMC 3396500. PMID 22711809.
- Haynes G (5 November 2010). "The catastrophic extinction of North American mammoths and mastodonts". World Archaeology. 33 (3): 391–416. doi:10.1080/00438240120107440.
- Carrasco MA, Barnosky AD, Graham RW (December 2009). "Quantifying the extent of North American mammal extinction relative to the pre-anthropogenic baseline". PLOS ONE. 4 (12): e8331. Bibcode:2009PLoSO...4.8331C. doi:10.1371/journal.pone.0008331. PMC 2789409. PMID 20016820.
- Richard L. Meehan (1999). "Whiston's Flood".
- Winchell, Alexander (1887). "Ignatius Donnelly's Comet". The Forum. IV: 105–115.
- Firestone R, West A, Warwick-Smith S (4 June 2006). The Cycle of Cosmic Catastrophes: How a Stone-Age Comet Changed the Course of World Culture. Bear & Company. p. 392. ISBN 978-1591430612.
- Firestone RB, West A, Kennett JP, Becker L, Bunch TE, Revay ZS, et al. (October 2007). "Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling". Proceedings of the National Academy of Sciences of the United States of America. 104 (41): 16016–21. Bibcode:2007PNAS..10416016F. doi:10.1073/pnas.0706977104. PMC 1994902. PMID 17901202.
- Haynes CV (May 2008). "Younger Dryas "black mats" and the Rancholabrean termination in North America". Proceedings of the National Academy of Sciences of the United States of America. 105 (18): 6520–5. Bibcode:2008PNAS..105.6520H. doi:10.1073/pnas.0800560105. PMC 2373324. PMID 18436643.
- Kennett DJ, Kennett JP, West A, Mercer C, Hee SS, Bement L, Bunch TE, Sellers M, Wolbach WS (January 2009). "Nanodiamonds in the Younger Dryas boundary sediment layer". Science. 323 (5910): 94. Bibcode:2009Sci...323...94K. doi:10.1126/science.1162819. PMID 19119227.
- Kerr RA (January 2009). "Planetary impacts. Did the mammoth slayer leave a diamond calling card?". Science. 323 (5910): 26. doi:10.1126/science.323.5910.26. PMID 19119192.
- Pinter N, Scott AC, Daulton TL, Podoll A, Koeberl C, Anderson RS, Ishman SE (2011). "The Younger Dryas impact hypothesis: A requiem". Earth-Science Reviews. 106 (3–4): 247. Bibcode:2011ESRv..106..247P. doi:10.1016/j.earscirev.2011.02.005.
- Pigati JS, Latorre C, Rech JA, Betancourt JL, Martínez KE, Budahn JR (May 2012). "Accumulation of impact markers in desert wetlands and implications for the Younger Dryas impact hypothesis". Proceedings of the National Academy of Sciences of the United States of America. 109 (19): 7208–12. Bibcode:2012PNAS..109.7208P. doi:10.1073/pnas.1200296109. PMC 3358914. PMID 22529347.
- Boslough M, Nicoll K, Holliday V, Daulton TL, Meltzer D, Pinter N, et al. (2013). "Arguments and Evidence Against a Younger Dryas Impact Event". In Giosan L, Fuller DQ, Nicoll K, Flad RK, Clift PD (eds.). Climates, Landscapes, and Civilizations. Geophysical Monograph Series. pp. 13–26. doi:10.1029/2012GM001209. ISBN 9781118704325.
- Daulton TL, Pinter N, Scott AC (September 2010). "No evidence of nanodiamonds in Younger-Dryas sediments to support an impact event". Proceedings of the National Academy of Sciences of the United States of America. 107 (37): 16043–7. Bibcode:2010PNAS..10716043D. doi:10.1073/pnas.1003904107. PMC 2941276. PMID 20805511.
- Roach J (22 June 2010). "Fungi, Feces Show Comet Didn't Kill Ice Age Mammals?". National Geographic Daily News. National Geographic Society. Retrieved 25 June 2010.
- Dalton, Rex (14 May 2011). "Comet Theory Comes Crashing to Earth". Pacific Standard. Retrieved 24 July 2019.
- Israde-Alcántara I, Bischoff JL, Domínguez-Vázquez G, Li HC, DeCarli PS, Bunch TE, et al. (March 2012). "Evidence from central Mexico supporting the Younger Dryas extraterrestrial impact hypothesis". Proceedings of the National Academy of Sciences of the United States of America. 109 (13): E738–47. Bibcode:2012PNAS..109E.738I. doi:10.1073/pnas.1110614109. PMC 3324006. PMID 22392980.
- Bundy FP (1967). "Hexagonal Diamond—A New Form of Carbon". Journal of Chemical Physics. 46 (9): 3437–3446. Bibcode:1967JChPh..46.3437B. doi:10.1063/1.1841236.
- Kaminskii FV, Blinova GK, Galimov EM, Gurkina GA, Klyuev YA, Kodina LA, et al. (1985). "Polycrystalline aggregates of diamond with lonsdaleite from Yakutian [Sakhan] placers". Mineral. Zhurnal. 7: 27–36.
- Petaev MI, Huang S, Jacobsen SB, Zindler A (August 2013). "Large Pt anomaly in the Greenland ice core points to a cataclysm at the onset of Younger Dryas". Proceedings of the National Academy of Sciences of the United States of America. 110 (32): 12917–20. Bibcode:2013PNAS..11012917P. doi:10.1073/pnas.1303924110. PMC 3740870. PMID 23878232.
- Petaev MI, Huang S, Jacobsen SB, Zindler A (August 2013). "Large Pt anomaly in the Greenland ice core points to a cataclysm at the onset of Younger Dryas". Proceedings of the National Academy of Sciences of the United States of America. 110 (32): 12917–20. Bibcode:2013PNAS..11012917P. doi:10.1073/pnas.1303924110. PMC 3740870. PMID 23878232.
- Boslough M (December 2013). "Greenland Pt anomaly may point to noncataclysmic Cape York meteorite entry". Proceedings of the National Academy of Sciences of the United States of America. 110 (52): E5035. Bibcode:2013PNAS..110E5035B. doi:10.1073/pnas.1320328111. PMC 3876257. PMID 24347646.
- Holliday V, Surovell T, Johnson E (8 July 2016). "A Blind Test of the Younger Dryas Impact Hypothesis". PLOS ONE. 11 (7): e0155470. Bibcode:2016PLoSO..1155470H. doi:10.1371/journal.pone.0155470. PMC 4938604. PMID 27391147.
- Daulton TL, Amari S, Scott AC, Hardiman M, Pinter N, Anderson RS (1 January 2017). "Comprehensive analysis of nanodiamond evidence relating to the Younger Dryas Impact Hypothesis". Journal of Quaternary Science. 32 (1): 7–34. Bibcode:2017JQS....32....7D. doi:10.1002/jqs.2892.
- Scott AC, Hardiman M, Pinter N, Anderson RS, Daulton TL, Ejarque A, Finch P, Carter-champion A (2017). "Interpreting palaeofire evidence from fluvial sediments: a case study from Santa Rosa Island, California, with implications for the Younger Dryas Impact Hypothesis". Journal of Quaternary Science. 32 (1): 35–47. Bibcode:2017JQS....32...35S. doi:10.1002/jqs.2914. ISSN 0267-8179.
- Daulton, TL, Amari, S, Scott, AC, Hardiman, MJ, Pinter, N & Anderson, R.S. 2017, Comprehensive analysis of nanodiamond evidence reported to support the Younger Dryas Impact Hypothesis Journal of Quaternary Science, vol. 32, no. 1, pp. 7–34.
- Moore CR, West A, LeCompte MA, Brooks MJ, Daniel IR, Goodyear AC, et al. (March 2017). "Widespread platinum anomaly documented at the Younger Dryas onset in North American sedimentary sequences". Scientific Reports. 7 (1): 44031. Bibcode:2017NatSR...744031M. doi:10.1038/srep44031. PMC 5343653. PMID 28276513.
- "impact-crater-found-under-hiawatha-glacier-greenland-ice". National Geographic.
- Wolbach WS, Ballard JP, Mayewski PA, Adedeji V, Bunch TE, Firestone RB, et al. (2018). "Extraordinary Biomass-Burning Episode and Impact Winter Triggered by the Younger Dryas Cosmic Impact ∼12,800 Years Ago. 1. Ice Cores and Glaciers". Journal of Geology. 126 (2): 165–184. Bibcode:2018JG....126..165W. doi:10.1086/695703.
- Wolbach WS, Ballard JP, Mayewski PA, Parnell AC, Cahill N, Adedeji V, et al. (2018). "Extraordinary Biomass-Burning Episode and Impact Winter Triggered by the Younger Dryas Cosmic Impact ∼12,800 Years Ago. 2. Lake, Marine, and Terrestrial Sediments". Journal of Geology. 126 (2): 185–205. Bibcode:2018JG....126..185W. doi:10.1086/695704.
- Holliday VT, Meltzer DJ (2010). "The 12.9-ka ET Impact Hypothesis and North American Paleoindians". Current Anthropology. 51 (5): 575–606. doi:10.1086/656015.
- Buchanan B, Collard M, Edinborough K (August 2008). "Paleoindian demography and the extraterrestrial impact hypothesis". Proceedings of the National Academy of Sciences of the United States of America. 105 (33): 11651–4. Bibcode:2008PNAS..10511651B. doi:10.1073/pnas.0803762105. PMC 2575318. PMID 18697936.
- Haynes G (2009). American megafaunal extinctions at the end of the Pleistocene. Springer. p. 125. ISBN 978-1-4020-8792-9. Retrieved 20 April 2012.
- Marlon JR, Bartlein PJ, Walsh MK, Harrison SP, Brown KJ, Edwards ME, et al. (February 2009). "Wildfire responses to abrupt climate change in North America". Proceedings of the National Academy of Sciences of the United States of America. 106 (8): 2519–24. Bibcode:2009PNAS..106.2519M. doi:10.1073/pnas.0808212106. PMC 2650296. PMID 19190185.
- Perkins S (23 April 2012). "No Love for Comet Wipeout".
- Pinter N, Ishman SE (2008). "Impacts, mega-tsunami, and other extraordinary claims". GSA Today. 18 (1): 37–38. doi:10.1130/GSAT01801GW.1.
- Haynes G (2009). "Introduction to the Volume". American Megafaunal Extinctions at the End of the Pleistocene. Vertebrate Paleobiology and Paleoanthropology. pp. 1–20. doi:10.1007/978-1-4020-8793-6_1. ISBN 978-1-4020-8792-9.
- Fiedel S (2009). "Sudden Deaths: The Chronology of Terminal Pleistocene Megafaunal Extinction". American Megafaunal Extinctions at the End of the Pleistocene. Vertebrate Paleobiology and Paleoanthropology. pp. 21–37. doi:10.1007/978-1-4020-8793-6_2. ISBN 978-1-4020-8792-9.
- Hubbe A, Hubbe M, Neves W (2007). "Early Holocene survival of megafauna in South America". Journal of Biogeography. 34 (9): 1642–1646. doi:10.1111/j.1365-2699.2007.01744.x.
- Stuart AJ, Kosintsev PA, Higham TF, Lister AM (October 2004). "Pleistocene to Holocene extinction dynamics in giant deer and woolly mammoth". Nature. 431 (7009): 684–9. Bibcode:2004Natur.431..684S. doi:10.1038/nature02890. PMID 15470427.
- Martin P (2005). "4 Ground Sloths at Home Cryptozoology, Ground Sloths, and Mapinguari National Park". Twilight of the mammoths: ice age extinctions and the rewilding of America. Berkeley: University of California Press. ISBN 978-0-520-23141-2.
- Barnosky AD (August 2008). "Colloquium paper: Megafauna biomass tradeoff as a driver of Quaternary and future extinctions". Proceedings of the National Academy of Sciences of the United States of America. 105 Suppl 1: 11543–8. Bibcode:2008PNAS..10511543B. doi:10.1073/pnas.0801918105. PMC 2556404. PMID 18695222.
- Scott E (2010). "Extinctions, scenarios, and assumptions: Changes in latest Pleistocene large herbivore abundance and distribution in western North America". Quat. Int. 217 (1–2): 225–239. Bibcode:2010QuInt.217..225S. doi:10.1016/j.quaint.2009.11.003.
- Gill JL, Williams JW, Jackson ST, Lininger KB, Robinson GS (November 2009). "Pleistocene megafaunal collapse, novel plant communities, and enhanced fire regimes in North America" (PDF). Science. 326 (5956): 1100–3. Bibcode:2009Sci...326.1100G. doi:10.1126/science.1179504. PMID 19965426.
- van Hoesel A, Hoek WZ, Braadbaart F, van der Plicht J, Pennock GM, Drury MR (May 2012). "Nanodiamonds and wildfire evidence in the Usselo horizon postdate the Allerod-Younger Dryas boundary". Proceedings of the National Academy of Sciences of the United States of America. 109 (20): 7648–53. Bibcode:2012PNAS..109.7648V. doi:10.1073/pnas.1120950109. PMC 3356666. PMID 22547791.
- Kerr RA (30 October 2010). "Mammoth-Killer Impact Rejected". Science NOW. AAAS.
- Tian H, Schryvers D, Claeys P (January 2011). "Nanodiamonds do not provide unique evidence for a Younger Dryas impact". Proceedings of the National Academy of Sciences of the United States of America. 108 (1): 40–4. Bibcode:2011PNAS..108...40T. doi:10.1073/pnas.1007695108. PMC 3017148. PMID 21173270.
- Paquay FS, Goderis S, Ravizza G, Vanhaeck F, Boyd M, Surovell TA, Holliday VT, Haynes CV, Claeys P (December 2009). "Absence of geochemical evidence for an impact event at the Bølling-Allerød/Younger Dryas transition". Proceedings of the National Academy of Sciences of the United States of America. 106 (51): 21505–10. Bibcode:2009PNAS..10621505P. doi:10.1073/pnas.0908874106. PMC 2799824. PMID 20007789.
- Surovell TA, Holliday VT, Gingerich JA, Ketron C, Haynes CV, Hilman I, Wagner DP, Johnson E, Claeys P (October 2009). "An independent evaluation of the Younger Dryas extraterrestrial impact hypothesis". Proceedings of the National Academy of Sciences of the United States of America. 106 (43): 18155–8. Bibcode:2009PNAS..10618155S. doi:10.1073/pnas.0907857106. PMC 2775309. PMID 19822748.
- Blaauw M, Holliday VT, Gill JL, Nicoll K (August 2012). "Age models and the Younger Dryas Impact Hypothesis". Proceedings of the National Academy of Sciences of the United States of America. 109 (34): E2240, author reply E2245–7. Bibcode:2012PNAS..109E2240B. doi:10.1073/pnas.1206143109. PMC 3427088. PMID 22829673.
- Boslough M (August 2012). "Inconsistent impact hypotheses for the Younger Dryas". Proceedings of the National Academy of Sciences of the United States of America. 109 (34): E2241, author reply E2245–7. Bibcode:2012PNAS..109E2241B. doi:10.1073/pnas.1206739109. PMC 3427067. PMID 22829675.
- Daulton TL (August 2012). "Suspect cubic diamond "impact" proxy and a suspect lonsdaleite identification". Proceedings of the National Academy of Sciences of the United States of America. 109 (34): E2242, author reply E2245–7. Bibcode:2012PNAS..109E2242D. doi:10.1073/pnas.1206253109. PMC 3427052. PMID 22829671.
- Gill JL, Blois JL, Goring S, Marlon JR, Bartlein PJ, Nicoll K, Scott AC, Whitlock C (August 2012). "Paleoecological changes at Lake Cuitzeo were not consistent with an extraterrestrial impact". Proceedings of the National Academy of Sciences of the United States of America. 109 (34): E2243, author reply E2245–7. Bibcode:2012PNAS..109E2243G. doi:10.1073/pnas.1206196109. PMC 3427112. PMID 22829674.
- Hardiman M, Scott AC, Collinson ME, Anderson RS (August 2012). "Inconsistent redefining of the carbon spherule "impact" proxy". Proceedings of the National Academy of Sciences of the United States of America. 109 (34): E2244, author reply E2245–7. Bibcode:2012PNAS..109E2244H. doi:10.1073/pnas.1206108109. PMC 3427080. PMID 22829672.
- Bement LC, Madden AS, Carter BJ, Simms AR, Swindle AL, Alexander HM, Fine S, Benamara M (February 2014). "Quantifying the distribution of nanodiamonds in pre-Younger Dryas to recent age deposits along Bull Creek, Oklahoma panhandle, USA". Proceedings of the National Academy of Sciences of the United States of America. 111 (5): 1726–31. Bibcode:2014PNAS..111.1726B. doi:10.1073/pnas.1309734111. PMC 3918833. PMID 24449875.
- Raines RT, Knowles JR (November 1987). "Enzyme relaxation in the reaction catalyzed by triosephosphate isomerase: detection and kinetic characterization of two unliganded forms of the enzyme". Biochemistry. 26 (22): 7014–20. Bibcode:2012PNAS..109E2245I. doi:10.1073/pnas.1209463109. PMC 3427057. PMID 3427057.
- Kennett JP, Kennett DJ, Culleton BJ, Aura Tortosa JE, Bunch TE, Erlandson JM, Johnson JR, Jordá Pardo JF, LeCompte MA, Mahaney WC, Tankersley KB, Wittke JH, Wolbach WS, West A (December 2015). "Reply to Holliday and Boslough et al.: Synchroneity of widespread Bayesian-modeled ages supports Younger Dryas impact hypothesis". Proceedings of the National Academy of Sciences of the United States of America. 112 (49): E6723–4. Bibcode:2015PNAS..112E6723K. doi:10.1073/pnas.1520411112. PMC 4679043. PMID 26604309.
- LeCompte MA, Goodyear AC, Demitroff MN, Batchelor D, Vogel EK, Mooney C, Rock BN, Seidel AW (October 2012). "Independent evaluation of conflicting microspherule results from different investigations of the Younger Dryas impact hypothesis". Proceedings of the National Academy of Sciences of the United States of America. 109 (44): E2960–9. doi:10.1073/pnas.1208603109. PMC 3497834. PMID 22988071.
- Napier WM, Bunch TE, Kennett JP, Wittke JH, Tankersley KB, Kletetschka G, Howard GA, West A (November 2013). "Reply to Boslough et al.: Decades of comet research counter their claims". Proceedings of the National Academy of Sciences of the United States of America. 110 (45): E4171. Bibcode:2013PNAS..110E4171N. doi:10.1073/pnas.1315467110. PMC 3831498. PMID 24350338.
- Wittke JH, Bunch TE, Kennett JP, Kennett DJ, Culleton BJ, Tankersley KB, Daniel IR, Kloosterman JB, Kletetschka G, West A, Firestone RB (October 2013). "Reply to van Hoesel et al.: Impact-related Younger Dryas boundary nanodiamonds from The Netherlands". Proceedings of the National Academy of Sciences of the United States of America. 110 (41): E3897–8. Bibcode:2013PNAS..110E3897W. doi:10.1073/pnas.1313207110. PMC 3799356. PMID 24244962.
- Boslough M, Harris AW, Chapman C, Morrison D (November 2013). "Younger Dryas impact model confuses comet facts, defies airburst physics". Proceedings of the National Academy of Sciences of the United States of America. 110 (45): E4170. Bibcode:2013PNAS..110E4170B. doi:10.1073/pnas.1313495110. PMC 3831451. PMID 24170865.
- Boslough M (April 2013). "Faulty protocols yield contaminated samples, unconfirmed results". Proceedings of the National Academy of Sciences of the United States of America. 110 (18): E1651. Bibcode:2013PNAS..110E1651B. doi:10.1073/pnas.1220567110. PMC 3645552. PMID 23599285.
- Reimold WU, Ferrière L, Deutsch A, Koeberl C (2014). "Impact controversies: Impact recognition criteria and related issues". Meteoritics & Planetary Science. 49 (5): 723–731. Bibcode:2014M&PS...49..723R. doi:10.1111/maps.12284. ISSN 1086-9379.
- Van Hoesel A, Hoek WZ, Pennock GM, Drury MR (2014). "The Younger Dryas impact hypothesis: a critical review". Quaternary Science Reviews. 83: 95–114. Bibcode:2014QSRv...83...95V. doi:10.1016/j.quascirev.2013.10.033.
- Meltzer DJ, Holliday VT, Cannon MD, Miller DS (May 2014). "Chronological evidence fails to support claim of an isochronous widespread layer of cosmic impact indicators dated to 12,800 years ago". Proceedings of the National Academy of Sciences of the United States of America. 111 (21): E2162–71. Bibcode:2014PNAS..111E2162M. doi:10.1073/pnas.1401150111. PMC 4040610. PMID 24821789.
- Holliday VT (December 2015). "Problematic dating of claimed Younger Dryas boundary impact proxies". Proceedings of the National Academy of Sciences of the United States of America. 112 (49): E6721. Bibcode:2015PNAS..112E6721H. doi:10.1073/pnas.1518945112. PMC 4679064. PMID 26604317.
- Thy P, Willcox G, Barfod GH, Fuller DQ (2015). "Anthropogenic origin of siliceous scoria droplets from Pleistocene and Holocene archaeological sites in northern Syria". Journal of Archaeological Science. 54: 193–209. doi:10.1016/j.jas.2014.11.027.
- Van der Hammen T, Van Geel B (2016). "Charcoal in soils of the Allerød-Younger Dryas transition were the result of natural fires and not necessarily the effect of an extra-terrestrial impact". Netherlands Journal of Geosciences. 87 (4): 359–361. doi:10.1017/S0016774600023416. ISSN 0016-7746.
- Roperch P, Gattacceca J, Valenzuela M, Devouard B, Lorand JP, Arriagada C, Rochette P, Latorre C, Beck P (2017). "Surface vitrification caused by natural fires in Late Pleistocene wetlands of the Atacama Desert". Earth and Planetary Science Letters. 469: 15–26. Bibcode:2017E&PSL.469...15R. doi:10.1016/j.epsl.2017.04.009. ISSN 0012-821X.
- Kjær KH, Larsen NK, Binder T, Bjørk AA, Eisen O, Fahnestock MA, et al. (November 2018). "A large impact crater beneath Hiawatha Glacier in northwest Greenland". Science Advances. 4 (11): eaar8173. Bibcode:2018SciA....4.8173K. doi:10.1126/sciadv.aar8173. PMC 6235527. PMID 30443592.
- Amos J (14 November 2018). "Greenland ice sheet hides huge 'impact crater'". BBC.com. BBC. Archived from the original on 13 January 2019. Retrieved 13 January 2019.
- Voosen P (14 November 2018). "Massive crater under Greenland's ice points to climate-altering impact in the time of humans". Sciencemag.org. Science. Archived from the original on 13 January 2019. Retrieved 13 January 2019.
- Patel NV (15 November 2018). "There's a giant crater the size of a city hiding under Greenland But not everyone agrees it's from an asteroid impact". Popsci.com. Popular Science. Archived from the original on 13 January 2019. Retrieved 13 January 2019.
- Hancock, Graham (1995). Fingerprints of the Gods: The Evidence of Earth's Lost Civilization. William Heinemann Ltd. p. 578. ISBN 978-0434313365.
- Flem-Ath, Rand; Flem-Ath, Rose (1995). When the Sky Fell: In Search of Atlantis. Trafalgar Square. ISBN 978-0297816287.
- Hancock, Graham (1995). Magicians of the Gods. Thomas Dunne Books. p. 528. ISBN 978-1250045928.
- Hancock, Graham (23 April 2019). America Before: The Key to Earth's Lost Civilization. St. Martin's Press. p. 608. ISBN 978-1250153739.
- "Joe Rogan Experience #1284". 22 April 2019.
- Kennett J (21 May 2013). "Comprehensive Analysis of Impact Spherules Supports Theory of Cosmic Impact 12,800 Years Ago". UC Santa Barbara.
- Holliday VT (2011). "A Cosmic Catastrophe: The Great Clovis Comet Debate: A personal perspective on an Outrageous Hypothesis". Argonaut Archaeological Research Fund. Tucson, Arizona: Department of Anthropology at the University of Arizona, University of Arizona.
- Pringle H (2008). "Firestorm from space wiped out prehistoric Americans". The New Scientist. 194 (2605): 8–9. doi:10.1016/S0262-4079(07)61277-9.
- West A, Goodyear A (2008). "The Clovis Comet: Part I:Evidence for a Cosmic Collision 12,900 Years Ago" (PDF). Mammoth Trumpet. 23 (1): 1–4.
- "Younger Dryas Boundary: Extraterrestrial Impact or Not" (PDF). www.georgehoward.net. Retrieved 15 April 2012.
- Hoffman C (2 July 2008). "Exploding Asteroid Theory Strengthened by New Evidence Located in Ohio, Indiana". University of Cincinnati. Retrieved 5 August 2008.
- "Science & Environment: Diamond clues to beasts' demise". BBC NEWS. 2 January 2009. Retrieved 15 April 2012.
- "Sciency Thoughts: Evidence for a Younger Dryas impact event?". 6 March 2012. Retrieved 15 April 2012.
- "The Younger Dryas Impact Hypothesis". Scientific American Blog Network. Retrieved 15 April 2012.
- "New Clovis-Age Comet Impact Theory". Retrieved 15 April 2012.
- Space Daily: Did A Massive Solar Proton Event Fry The Earth?