Younger Dryas impact hypothesis
[5][6][7] In 2007, the first YDIH paper[8] speculated that a comet airburst over North America created a Younger Dryas boundary (YDB) layer; however, inconsistencies have been identified in other published results.
;[14] 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.
[31] Some scientists have asserted that the carbon spherules originated as fungal structures and/or insect fecal pellets, and contained modern contaminants[32][33] and that the claimed nanodiamonds are actually misidentified graphene and graphene/graphane oxide aggregates.
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.
[36][37] 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.
[44][45][46][47][48] 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.
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.
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.
[68] 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.
[62] 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,[69] possibly from anthropogenic activities, including hunting.
[71] 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.
[77] 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.
[79] 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.
Geological evidence for such an event is not fully secure,[83] 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.
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.
"[91] 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.
[1] 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.
[92] 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.
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.
[102] 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/[5][103] 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.
[105][106] In 2009, papers by Kerr [107] and Kennett [108] 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.
[125] 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][128] 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.
[133] 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".
[9] 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."
17 In a December 2023 article by CR Moore and others[134] 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.
[h][138][139][140] 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.
[146] In 2017, a debate was held on the Joe Rogan Experience between proponents[clarification needed] Graham Hancock, Randall Carlson, and Malcolm A. LeCompte and opponents Michael Shermer and Marc J.
[150] A 2021 episode of the Science Channel series Ancient Unexplained Files had a segment on the evidence from Abu Hureyra;[129] geoscientist Sian Proctor also described the impact hypothesis as a whole.
[2] 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:
