Younger Dryas impact hypothesis

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The Younger Dryas impact hypothesis (YDIH) proposes that the onset of the Younger Dryas (YD) cool period (stadial) at the end of the Last Glacial Period, around 12,900 years ago was the result of some kind of extraterrestrial event with specific details varying between publications^{[1]: Sec 1}. The hypothesis is controversial and not widely accepted by relevant experts.^[2][1][3]

It is an alternative to the long-standing and widely accepted explanation that it was caused by a significant reduction in, or shutdown of the

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.[21] They argue that there is a synchronous Younger Dryas boundary layer that should be used as a local,^[22] or even global^[23] 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."^[24] In 2011, a review of the evidence lead 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."^[25] 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.^{[1]: Sec 3.2} Another example is that of extensive wildfires claimed by some YDIH proponents^[26] that has been refuted by experts.^{[27] [1]: 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."^[1]

Hypothetical impact markers

Proponents have reported materials including

Some scientists have asserted that the carbon spherules originated as fungal structures and/or insect fecal pellets, and contained modern contaminants[30]^[31] and that the claimed nanodiamonds are actually misidentified graphene and graphene/graphane oxide aggregates.^[32][33] Interestingly, Allen West and James Kennett had filed a patent for the formation of nanodiamonds on Jan 22, 2009 with a provisional patent roughly one year prior^[34] 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.^[35][36] 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.^[37] 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).^[a][38][40] The original authors argued that these concentrations were still >300% (a factor of 3) above background in 2 of their samples.^[41] Another group was unable to confirm prior claims of magnetic particles and microspherules in 2009,^[42] 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.^{[43][44][45][46][47]}

"Black mats"

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.^[b] 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.^[50] In 2019, Jorgeson and others tested this conclusion with the simulation of radiocarbon ages.^[51] 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.^[51]

Marlon et al. suggest that wildfires were a consequence of rapid climate change.^[52] "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.^[53] Research published in 2012 has shown that the so-called "black mats" are easily explained by typical earth processes in wetland environments.^[c][54] 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 wetland systems and not as a result of catastrophic bolide impacts.^[c][54]

Researchers have also criticized the conclusions of various studies for incorrect age-dating of the sediments,^[55] contamination by modern carbon, inconsistent hypothesis that made it difficult to predict the type and size of bolide,^[56] lack of proper identification of lonsdaleite,^[57] confusing an extraterrestrial impact with other causes such as fire,^[58] and for inconsistent use of the carbon spherule "proxy".^[59] Naturally occurring lonsdaleite has also been identified in non-bolide diamond placer deposits in the Sakha Republic.^[60]

Extinction of megafauna

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.^[61][62][63] The extinction of woolly mammoths in Siberia also appears to have occurred later than in North America.^[61] 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,^[61][62][64] and the survival of ground sloths in the Antilles,^[65] the Caribbean, until 4700 cal BP.^[61] The Australian megafaunal extinctions occurred approximately 30,000 years earlier than the hypothetical Younger Dryas event.^[66]

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.^[67] 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.^[61] 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,^[68] possibly from anthropogenic activities, including hunting.^[69]

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.^[70] 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.^{[71][needs update]}

Impact on human societies

A study of

A 2018 paper reported the discovery of an impact crater under the Hiawatha Glacier in Greenland of unknown age.^[78] 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.^[79]

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.^[d][80][81]

Other explanations

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

Mainstream explanation

The most widely accepted explanation is that it began because of a significant reduction or

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.^[86]

Another proposed cause has been volcanic activity.^[87][88] 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.^[89] 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."^[90]

History

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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

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.^[101]

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/^[4][102] 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.^[9] 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.^[7]

In 2008,

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.

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.^[109] Skepticism increased when it was reported that one of the lead authors of the original paper had practiced geophysics without a license.^{[f][110][111]} Around that time, Daulton stated that no nanodiamonds were found^[32] and that the supposed carbon spherules could be fungus or insect feces and included modern contaminants as stated by Boslough and others^[30] and Roach.^[31] 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.^[28]

In 2012, a paper by Bunch and others reported the discovery of scoria like objects (SLO) and stated that they were consistent with a extraterrestrial impact or airburst.

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.[117] Also that year, Daulton and others reported an analysis of nanodiamond evidence failed to uncover lonsdaleite or a spike in nanodiamond concentration at the YDB.^[118]

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.^[119]

In 2018, dealing with an "extraordinary biomass-burning episode" associated with the Younger Dryas Impact were reported by Wolbach and others ^[120][121] and Lynch.^[122] However, these claims of extraordinary fires are disputed by Holliday and others^[123]with a response by Wolbach.^[124]

In 2019, Pino and others reported evidence in sediment layers with

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.[127]

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.^[128][129]

In 2020, a group led by Andrew M. T. Moore found 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.^{[130][131][132]} However, samples from the site no longer exist so these results cannot be confirmed.^[133]

In 2022, a paper by geologist James L. Powell, a YDIH proponent, claimed that opponents had prematurely rejected YDIH,^[134] detailing the example of research published by Firestone and others in 2001^[91] and the inability of a later study by Surovell and others in 2009^[42] that was unable to reproduce these results leading a number of other scientists to reject YDIH.^{[134]: Table 4} Powell argues that since then, many independent studies have reproduced that evidence at dozens of YD sites.^[134]

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".^[2]

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In July 2023 Holliday and others published a comprehensive refutation of the YDIH^[1] 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,^{[1]: Sec. 8-12} "Black mats,"^{[1]: Sec. 6} Extinction of megafauna,^{[1]: Sec. 3.2} Impact on human societies,^{[1]: Sec. 3.1} the Hiawatha crater.^{[1]: Sec. 7} Also criticized were fundamental assumptions,^{[1]: Sec. 3} flawed sampling,^{[1]: Sec. 4} inadequate dating,^{[1]: Sec. 5} Pseudoarchaeological divined date of the impact event,^{[1]: Sec. 5.2} pseudoscience (fringe) evidence and conjecture,^{[1]: Sec. 14} issues with other YDIH claims, such as the Carolina bays, ^{[1]: Sec. 13.1} contradictory results when different groups have examined the same sample specimens, ^{[1]: Sec. 14} and unparalleled promotion of YDIH outside of scientific literature. ^{[1]: Sec. 14} The paper also responded to and critiqued assertions from Powell.^[11] 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.^{[1]: Sec. 17}

In a December 2023 article by CR Moore and others^[135] 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."

In popular culture

The impact hypothesis has been the subject of documentaries,

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.^[142][143] These claims were criticized as inaccurate by independent reviewers, including Jason Colavito, Michael Shermer, and Marc J. Defant.^{[g][144][145][146]} 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.^[147]

In 2017, a debate was held on the

A 2021 episode of the Science Channel series Ancient Unexplained Files had a segment on the evidence from Abu Hureyra;^[130] geoscientist Sian Proctor also described the impact hypothesis as a whole.^[152]

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 conclusion that many attributes of the series are pseudoscience.^[2]

See also

• Carolina bays – Elliptical depressions concentrated along the Atlantic seaboard of North America
• Murray Springs Clovis Site – Archaeological site in Arizona, United States
• Shiva hypothesis – Scientific theory concerning impact events
• Taurids – Annual meteor shower
• Tollmann's bolide hypothesis – Hypothetical impact event
• Tunguska event and Chelyabinsk meteor - two examples of meteors exploding in the atmosphere

Footnotes

References

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Bibliography

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Further reading

• Bentley M (2 January 2009). "Diamond clues to beasts' demise". BBC News. Archived from the original on 3 September 2010. Retrieved 15 April 2012.
• Bressan D (27 July 2011). "The Younger Dryas Impact Hypothesis". Scientific American Blog Network. Archived from the original on 15 March 2013. Retrieved 15 April 2012.
• Fernandez S (21 May 2013). "Comprehensive Analysis of Impact Spherules Supports Theory of Cosmic Impact 12,800 Years Ago". UC Santa Barbara. Archived from the original on 16 February 2021. Retrieved 24 June 2021.
• Firestone RB (24 July 2019). "Disappearance of Ice Age Megafauna and the Younger Dryas Impact". Capeia. Archived from the original on 10 April 2021. Retrieved 30 June 2021.
• Hoffman C (2 July 2008). "Exploding Asteroid Theory Strengthened by New Evidence Located in Ohio, Indiana". University of Cincinnati. Archived from the original on 31 July 2008. Retrieved 5 August 2008.
• 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. Archived from the original on 5 March 2016. Retrieved 14 July 2011.
• doi:10.1016/S0262-4079(07)61277-9. Archived
  from the original on 14 September 2012. Retrieved 19 September 2017.
• Sweatman, Martin B. (July 2021). "The Younger Dryas impact hypothesis: Review of the impact evidence" (PDF).
  S2CID 236231169
  .

Presentations of the American Geophysical Union

• "Younger Dryas Boundary: Extraterrestrial Impact or Not II" (PDF). American Geophysical Union Fall Meeting, San Francisco, California. 16 December 2009. Archived from the original (PDF) on 6 February 2012. Retrieved 15 April 2012.
• "Younger Dryas Boundary: Extraterrestrial Impact or Not I" (PDF). American Geophysical Union Fall Meeting, San Francisco, California. 16 December 2009. Archived from the original (PDF) on 23 April 2020. Retrieved 24 June 2021.

Mammoth Trumpet

An extensive series of articles was published in Mammoth Trumpet, the magazine for Texas A&M University's Center for the Study of the First Americans, featuring conversations with many YDIH proponents and opponents:

• Largent F (January 2008). "The Clovis Comet - Part I: Evidence for a Cosmic Collision 12,900 Years Ago" (PDF). Mammoth Trumpet. 23 (1): 1-3, 19-20.
  Wikidata Q107225241
  .
• Largent F (April 2008). "The Clovis Comet - Part II: What the Data Tell Us" (PDF). Mammoth Trumpet. 23 (2): 15–18.
  Wikidata Q107226201
  .
• Largent F (July 2008). "The Clovis Comet - Part III: The Implications" (PDF). Mammoth Trumpet. 23 (3): 18–20.
  Wikidata Q107226305
  .
• Largent F (October 2008). "The Clovis Comet - Part IV: The Scientific Community Responds" (PDF). Mammoth Trumpet. 23 (4): 13–15.
  Wikidata Q107226371
  .
• Lepper B (October 2009). "Fire Record Undercuts Clovis Comet Theory" (PDF). Mammoth Trumpet. 24 (4): 4–7.
  Wikidata Q107228406
  .
• Largent F (April 2010). "The Clovis Comet Revisited - In the Crucible of Scientific Inquiry" (PDF). Mammoth Trumpet. 25 (2): 15–19.
  Wikidata Q107228547
  .
• Largent F (July 2011). "The Clovis Comet Revisited - The Nanodiamond Controversy, Part I" (PDF). Mammoth Trumpet. 26 (3): 1-4, 8.
  Wikidata Q107228612
  .
• Largent F (October 2011). "The Clovis Comet Revisited - The Nanodiamond Controversy, Part II: A Case of Mistaken Identity?" (PDF). Mammoth Trumpet. 26 (4): 1-3, 20.
  Wikidata Q107228963
  .
• Largent F (July 2014). "The Clovis Comet - The Cratering Evidence" (PDF). Mammoth Trumpet. 29 (3): 1-5, 9.
  Wikidata Q107229168
  .
• Largent F (January 2015). "The Clovis Comet - New Developments in the Proxy Evidence, Part I" (PDF). Mammoth Trumpet. 30 (1): 11–14.
  Wikidata Q107229501
  .
• Largent F (April 2015). "The Clovis Comet - New Developments in the Proxy Evidence, Part II" (PDF). Mammoth Trumpet. 30 (2): 15–19.
  Wikidata Q107230043
  .
• Largent F (October 2015). "The Clovis Comet - New Developments in the Proxy Evidence, Part III" (PDF). Mammoth Trumpet. 30 (4): 17–20.
  Wikidata Q107230085
  .

External links

Scholia has a profile for Younger Dryas impact hypothesis (Q1092095).

• Media related to Younger Dryas impact hypothesis at Wikimedia Commons