Reply to Holliday and Boslough et al.: Synchroneity of widespread Bayesian-modeled ages supports Younger Dryas impact hypothesis

Kennett, James P.; Kennett, Douglas J.; Culleton, Brendan J.; Tortosa, J. Emili Aura; Bunch, T. E.; Erlandson, Jon M.; Johnson, John R.; Pardo, Jesús F. Jordá; LeCompte, Malcome A.; Mahaney, William C.; Tankersley, Kenneth B.; Wittke, J. H.; Wolbach, Wendy S.; West, Allen

doi:10.1073/pnas.1520411112

Cited by 8 publications

(8 citation statements)

References 9 publications

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“…The purported impact proxies at Bull Creek are older than ~12,935 cal yrs BP by some unknown age and also are found in abundance in strata <3000 yrs old. Contrary to Kennett et al [ 50 ], these issues of purported impact indicators appearing in sections older and younger than the YDB have never been addressed by YDIH proponents.…”

Section: Resultsmentioning

confidence: 86%

“…Measured levels of OC are low [ 27 ], but that trend (dark gray to black color but low OC) is common for organic-rich soils and sediments buried for even a few hundred years [ 56 ]. The association of claimed impact proxies with organic-rich sediment and soils, independent of their age, has been noted since the initial publications by Firestone et al [ 1 , 2 ] [ 4 , 7 , 16 , 36 , 43 , 50 , 57 ]. According to investigations by YDIH proponents, the YDB zone is associated with a “black mat” (i.e., soils or sediments high in organic matter [ 58 , 59 ]) at 15 of 29 key localities [ 19 ].…”

Section: Resultsmentioning

confidence: 99%

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A Blind Test of the Younger Dryas Impact Hypothesis

2016

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The Younger Dryas Impact Hypothesis (YDIH) states that North America was devastated by some sort of extraterrestrial event ~12,800 calendar years before present. Two fundamental questions persist in the debate over the YDIH: Can the results of analyses for purported impact indicators be reproduced? And are the indicators unique to the lower YD boundary (YDB), i.e., ~12.8k cal yrs BP? A test reported here presents the results of analyses that address these questions. Two different labs analyzed identical splits of samples collected at, above, and below the ~12.8ka zone at the Lubbock Lake archaeological site (LL) in northwest Texas. Both labs reported similar variation in levels of magnetic micrograins (>300 mg/kg >12.8ka and <11.5ka, but <150 mg/kg 12.8ka to 11.5ka). Analysis for magnetic microspheres in one split, reported elsewhere, produced very low to nonexistent levels throughout the section. In the other split, reported here, the levels of magnetic microspherules and nanodiamonds are low or nonexistent at, below, and above the YDB with the notable exception of a sample <11,500 cal years old. In that sample the claimed impact proxies were recovered at abundances two to four orders of magnitude above that from the other samples. Reproducibility of at least some analyses are problematic. In particular, no standard criteria exist for identification of magnetic spheres. Moreover, the purported impact proxies are not unique to the YDB.

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Section: Resultsmentioning

confidence: 86%

Section: Resultsmentioning

confidence: 99%

A Blind Test of the Younger Dryas Impact Hypothesis

2016

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“…There is supporting evidence of an extraterrestrial impact coinciding with the onset of YD cooling—for example, recent work by Moore et al (2020) in Abu Hureyra, Syria, but see also Bunch et al (2012); Kennett et al (2009); Kinzie et al (2014); Kurbatov et al (2010); Mahaney et al (2013); Wittke et al (2013); Wu et al (2013); and Israde‐Alcantara et al (2018). The YDB impact hypothesis, originally proposed by Firestone et al (2007), addresses stratigraphic signatures inconsistent with terrestrial activity, such as depositions of magnetic grains with Ir in the black mat; magnetic, silicate, and carbon spherules with signatures of minerals formed at high temperatures (>2000°C) and high‐temperature SiO 2 meltglass and melt accretions, corundum, suessite (Fe 3 Si, formed in extreme temperatures), nanodiamonds, fullerenes (highly symmetrical and stable carbon molecules) with extraterrestrial He, as well as Pt and Ni deposits.…”

Section: Introductionmentioning

confidence: 77%

Main Belt asteroid as a Possible Younger Dryas impactor

Usatov¹

2020

Astron Nachr

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The Younger Dryas (YD) cosmic impact hypothesis is gaining support due to the increasing amount of proxy evidence from 26 Younger Dryas Boundary sites that includes depositions of magnetic, silicate, and carbon spherules; high‐temperature meltglass and melt accretions; nanodiamonds, and Ir and Pt deposits, as well as evidence of major biomass burning and widespread extinctions in stratigraphic layers dated ∼12.8 kyr ago. Among the possible causes, an encounter with a swarm of fragments on an orbit similar to that of 2P/Encke is proposed. This work suggests another potential source of impacting material that requires no special events in the Solar System: Main Belt asteroids excited into highly eccentric Earth‐crossing orbits via mean‐motion resonance with Jupiter and the ν6 secular resonance with Saturn—the established mechanisms of Main Asteroid Belt depletion and Earth‐bound meteorite delivery. It is shown that the probability of and the time between collisions of ejected material with Earth (Δt ∼ 32 kyr), as well as the energy of impacts, are broadly compatible with the YD impact proxy evidence. Such events may reoccur via bombardments of fragment swarms, potentially challenging existing asteroid deflection concepts.

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“…Evidence given in support of this possible cosmic impact, at least for the northern hemisphere, are spikes in nanodiamonds 10,11 , platinum 12 , magnetic and glassy impact-related spherules, high-temperature minerals and melt glass, carbon spherules and/or osmium at the onset of the Younger Dryas 9 .…”

Section: The Younger Dryas and A Cosmic Impact?mentioning

confidence: 96%

temperature index in a Late Quaternary sequence at Wonderkrater, South Africa

Thackeray¹

2018

S. Afr. J. Sci.

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Reply to Holliday and Boslough et al.: Synchroneity of widespread Bayesian-modeled ages supports Younger Dryas impact hypothesis

Cited by 8 publications

References 9 publications

A Blind Test of the Younger Dryas Impact Hypothesis

A Blind Test of the Younger Dryas Impact Hypothesis

Main Belt asteroid as a Possible Younger Dryas impactor

temperature index in a Late Quaternary sequence at Wonderkrater, South Africa

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