Younger Dryas impact hypothesis

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 North Atlantic Conveyor due to a sudden influx of freshwater from Lake Agassiz and deglaciation in North America.^[4]^[5]^[6]^[7]^{[excessive citations]} A 1997 analysis suggested that to create continent-wide damage a 4 km comet^[8]^{: Fig. 1} direct impact would be required, or that the same damage could be caused by a smaller disintegrating comet airburst.^[8]^{: Fig. 5} In 2007, the first YDIH paper^[9] speculated that a comet airburst over North America created a Younger Dryas boundary (YDB) layer; however, inconsistencies have been identified in other published results.^[1] And authors have not yet responded to requests for clarification and have never made their raw data available.^[10]^{[better source needed]} Some YDIH proponents have also proposed that this event triggered extensive biomass burning, a brief impact winter that destabilized the Atlantic Conveyor and triggered the Younger Dryas instance of abrupt climate change,^[9]^{: p. 16021} contributed to extinctions of late Pleistocene megafauna, and resulted in the disappearance of the Clovis culture.^[11]^[12]

^ ^a ^b ^c Holliday, Vance T.; Daulton, Tyrone L.; Bartlein, Patrick J.; Boslough, Mark B.; Breslawski, Ryan P.; Fisher, Abigail E.; Jorgeson, Ian A.; Scott, Andrew C.; Koeberl, Christian; Marlon, Jennifer; Severinghaus, Jeffrey; Petaev, Michail I.; Claeys, Philippe (26 July 2023). "Comprehensive refutation of the Younger Dryas Impact Hypothesis (YDIH)". Earth-Science Reviews. 247: 104502. Bibcode:2023ESRv..24704502H. doi:10.1016/j.earscirev.2023.104502.
^ Cite error: The named reference :0 was invoked but never defined (see the help page).
^ Powell (2022).
^ Dalton R (16 May 2007). "Blast in the past?". Nature. 447 (7142): 256–257. Bibcode:2007Natur.447..256D. doi:10.1038/447256a. PMID 17507957. S2CID 11927411.
^ Broecker WS (2006). "Was the Younger Dryas Triggered by a Flood?". Science. 312 (5777): 1146–1148. doi:10.1126/science.1123253. PMID 16728622. S2CID 39544213.
^ Sun et al. (2020), p. 1: "The prevailing hypothesis is that the cooling and stratification of the North Atlantic Ocean were a consequence of massive ice sheet discharge of meltwater and icebergs and resulted in reduction or cessation of the North Atlantic Conveyor."
^ Jones, N (2 September 2013). "Evidence found for planet-cooling asteroid". Nature. doi:10.1038/nature.2013.13661. S2CID 131715496.
^ ^a ^b Toon, Owen B.; Zahnle, Kevin; Morrison, David; Turco, Richard P.; Covey, Curt (February 1997). "Environmental perturbations caused by the impacts of asteroids and comets". Reviews of Geophysics. 35 (1): 41–78. Bibcode:1997RvGeo..35...41T. doi:10.1029/96RG03038. ISSN 8755-1209.
^ ^a ^b Firestone RB, West A, Kennett JP, Becker L, Bunch TE, Revay ZS, Schultz PH, Belgya T, et al. (9 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.
^ Firestone RB, West A, Kennett JP, Becker L, Bunch TE, Revay ZS, Schultz PH, Belgya T, et al. (9 October 2007). "Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling". PubPeer. Retrieved 16 August 2022.
^ Powell (2022), p. 1: "The hypothesis proposes that the airburst or impact of a comet ~12,850 years ago caused the ensuing ~1200-year-long Younger Dryas (YD) cool period and contributed to the extinction of the Pleistocene megafauna in the Western Hemisphere and the disappearance of the Clovis PaleoIndian culture."
^ Pino et al. (2019), p. 1: "The Younger Dryas (YD) impact hypothesis posits that fragments of a large, disintegrating asteroid/comet struck North America, South America, Europe, and western Asia ~12,800 years ago. Multiple airbursts/impacts produced the YD boundary layer (YDB), depositing peak concentrations of platinum, high-temperature spherules, meltglass, and nanodiamonds, forming an isochronous datum at >50 sites across ~50 million km² of Earth's surface. This proposed event triggered extensive biomass burning, brief impact winter, YD climate change, and contributed to extinctions of late Pleistocene megafauna."

[:1-1] Holliday, Vance T.; Daulton, Tyrone L.; Bartlein, Patrick J.; Boslough, Mark B.; Breslawski, Ryan P.; Fisher, Abigail E.; Jorgeson, Ian A.; Scott, Andrew C.; Koeberl, Christian; Marlon, Jennifer; Severinghaus, Jeffrey; Petaev, Michail I.; Claeys, Philippe (26 July 2023). "Comprehensive refutation of the Younger Dryas Impact Hypothesis (YDIH)". Earth-Science Reviews. 247: 104502. Bibcode:2023ESRv..24704502H. doi:10.1016/j.earscirev.2023.104502.

[:0-2] Cite error: The named reference :0 was invoked but never defined (see the help page).

[FOOTNOTEPowell2022-3] Powell (2022).

[Dalton-4] Dalton R (16 May 2007). "Blast in the past?". Nature. 447 (7142): 256–257. Bibcode:2007Natur.447..256D. doi:10.1038/447256a. PMID 17507957. S2CID 11927411.

[Broecker-5] Broecker WS (2006). "Was the Younger Dryas Triggered by a Flood?". Science. 312 (5777): 1146–1148. doi:10.1126/science.1123253. PMID 16728622. S2CID 39544213.

[6] Sun et al. (2020), p. 1: "The prevailing hypothesis is that the cooling and stratification of the North Atlantic Ocean were a consequence of massive ice sheet discharge of meltwater and icebergs and resulted in reduction or cessation of the North Atlantic Conveyor."

[NJones-7] Jones, N (2 September 2013). "Evidence found for planet-cooling asteroid". Nature. doi:10.1038/nature.2013.13661. S2CID 131715496.

[:6-8] Toon, Owen B.; Zahnle, Kevin; Morrison, David; Turco, Richard P.; Covey, Curt (February 1997). "Environmental perturbations caused by the impacts of asteroids and comets". Reviews of Geophysics. 35 (1): 41–78. Bibcode:1997RvGeo..35...41T. doi:10.1029/96RG03038. ISSN 8755-1209.

[PNAS07A-9] Firestone RB, West A, Kennett JP, Becker L, Bunch TE, Revay ZS, Schultz PH, Belgya T, et al. (9 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.

[10] Firestone RB, West A, Kennett JP, Becker L, Bunch TE, Revay ZS, Schultz PH, Belgya T, et al. (9 October 2007). "Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling". PubPeer. Retrieved 16 August 2022.

[:2-11] Powell (2022), p. 1: "The hypothesis proposes that the airburst or impact of a comet ~12,850 years ago caused the ensuing ~1200-year-long Younger Dryas (YD) cool period and contributed to the extinction of the Pleistocene megafauna in the Western Hemisphere and the disappearance of the Clovis PaleoIndian culture."

[12] Pino et al. (2019), p. 1: "The Younger Dryas (YD) impact hypothesis posits that fragments of a large, disintegrating asteroid/comet struck North America, South America, Europe, and western Asia ~12,800 years ago. Multiple airbursts/impacts produced the YD boundary layer (YDB), depositing peak concentrations of platinum, high-temperature spherules, meltglass, and nanodiamonds, forming an isochronous datum at >50 sites across ~50 million km² of Earth's surface. This proposed event triggered extensive biomass burning, brief impact winter, YD climate change, and contributed to extinctions of late Pleistocene megafauna."

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