Very high-temperature impact melt products as evidence for cosmic airbursts and impacts 12,900 years ago

Abstract

It has been proposed that fragments of an asteroid or comet impacted Earth, deposited silica-and iron-rich microspherules and other proxies across several continents, and triggered the Younger Dryas cooling episode 12,900 years ago. Although many independent groups have confirmed the impact evidence, the hypothesis remains controversial because some groups have failed to do so. We examined sediment sequences from 18 dated Younger Dryas boundary (YDB) sites across three continents (North America, Europe, and Asia), spanning 12,000 km around nearly one-third of the planet. All sites display abundant microspherules in the YDB with none or few above and below. In addition, three sites (Abu Hureyra, Syria; Melrose, Pennsylvania; and Blackville, South Carolina) display vesicular, high-temperature, siliceous scoria-like objects, or SLOs, that match the spherules geochemically. We compared YDB objects with melt products from a known cosmic impact (Meteor Crater, Arizona) and from the 1945 Trinity nuclear airburst in Socorro, New Mexico, and found that all of these high-energy events produced material that is geochemically and morphologically comparable, including: (i) high-temperature, rapidly quenched microspherules and SLOs; (ii) corundum, mullite, and suessite (Fe 3 Si), a rare meteoritic mineral that forms under high temperatures; (iii) melted SiO 2 glass, or lechatelierite, with flow textures (or schlieren) that form at >2,200°C; and (iv) particles with features indicative of high-energy interparticle collisions. These results are inconsistent with anthropogenic, volcanic, authigenic, and cosmic materials, yet consistent with cosmic ejecta, supporting the hypothesis of extraterrestrial airbursts/impacts 12,900 years ago. The wide geographic distribution of SLOs is consistent with multiple impactors.tektite | microcraters | oxygen fugacity | trinitite Manuscript TextThe discovery of anomalous materials in a thin sedimentary layer up to a few cm thick and broadly distributed across several continents led Firestone et al. (1) to propose that a cosmic impact (note that "impact" denotes a collision by a cosmic object either with Earth's surface, producing a crater, or with its atmosphere, producing an airburst) occurred at 12.9 kiloannum (ka; all dates are in calendar or calibrated ka, unless otherwise indicated) near the onset of the Younger Dryas (YD) cooling episode. This stratum, called the YD boundary layer, or YDB, often occurs directly beneath an organic-rich layer, referred to as a black mat (2), that is distributed widely over North America and parts of South America, Europe, and Syria. Black mats also occur less frequently in quaternary deposits that are younger and older than 12.9 ka (2). The YDB layer contains elevated abundances of iron-and silica-rich microspherules (collectively called "spherules") that are interpreted to have originated by cosmic impact because of their unique properties, as discussed below. Other markers include sediment and magnetic grains with elevated iridium concentrations and exot...

Nanodiamond-Rich Layer across Three Continents Consistent with Major Cosmic Impact at 12,800 Cal BP

“…The proposed impact deposited the YDB layer, which contains many cosmic-impact proxies, including magnetic and glassy impact spherules, iridium, fullerenes, carbon spherules, glass-like carbon, charcoal, and aciniform carbon, a form of soot (Firestone et al 2007;Wittke et al 2013). In North America and the Middle East, Bunch et al (2012) identified YDB melt-glass that formed at high temperatures (1730Њ to 12200ЊC), as also reported by three independent groups, Mahaney et al (2010) in South America and Fayek et al (2012) and Wu et al (2013) in North America. This study focuses solely on nanodiamonds (NDs), and so, for independent discussions of other proxies, see Haynes et al (2010) and Paquay et al (2009), who found no evidence for the platinum-group elements iridium or osmium.…”

“…Details on site setting, geological information, and dating are in tables D2, D3. More details for most sites are in Bunch et al (2012) and Wittke et al (2013). Dating and Age-Depth Models.…”

“…After those roots decayed or burned, the resulting cavity filled with sediment containing younger charcoal and carbon spherules that mixed with the older carbon material. Because this is a common occurrence where the YDB is shallow, radiocarbon dating is unreliable for such sites and OSL dating is preferred (Bunch et al 2012), as indicated by the older OSL date for the Gainey site. No matter the cause, the ages of these two sites remain poorly constrained.…”

“…The YDB hypothesis posits that only one impact occurred, producing coeval, above-background peaks in NDs, iridium (Firestone et al 2007), platinum (Petaev et al 2013), osmium (Wu et al 2013), high-temperature melt-glass (1730Њ to 12200ЊC; Bunch et al 2012), and high-temperature magnetic spherules (11500ЊC; Wittke et al 2013). Others have proposed various age models for deposition of the YDB proxies.…”

Independent evaluation of conflicting microspherule results from different investigations of the Younger Dryas impact hypothesis

“…To examine this discrepancy, we conducted an independent blind investigation of two sites common to both studies, and a third site investigated only by Surovell Firestone et al) proposed that a cosmic impact event occurred at the onset of the Younger Dryas (YD) cooling episode at about 12,900 calendar years Before Present (12.9 ka B.P.). Evidence cited to support their hypothesis includes elevated levels of iron-and silica-rich magnetic spherules, magnetic grains, iridium, and other materials such as nanodiamonds and high temperature melt glass, in association with proxies indicative of biomass burning (1)(2)(3)(4)(5). Also reported were charcoal, carbon spherules, aciniform soot, and glass-like carbon.…”