No evidence of nanodiamonds in Younger–Dryas sediments to support an impact event

Abstract

The causes of the late Pleistocene megafaunal extinctions in North America, disappearance of Clovis paleoindian lithic technology, and abrupt Younger-Dryas (YD) climate reversal of the last deglacial warming in the Northern Hemisphere remain an enigma. A controversial hypothesis proposes that one or more cometary airbursts/ impacts barraged North America ≈12,900 cal yr B.P. and caused these events. Most evidence supporting this hypothesis has been discredited except for reports of nanodiamonds (including the rare hexagonal polytype) in Bølling-Ållerod-YD-boundary sediments. The hexagonal polytype of diamond, lonsdaleite, is of particular interest because it is often associated with shock pressures related to impacts where it has been found to occur naturally. Unfortunately, previous reports of YD-boundary nanodiamonds have left many unanswered questions regarding the nature and occurrence of the nanodiamonds. Therefore, we examined carbon-rich materials isolated from sediments dated 15,818 cal yr B.P. to present (including the Bølling-Ållerod-YD boundary). No nanodiamonds were found in our study. Instead, graphene-and graphene/ graphane-oxide aggregates are ubiquitous in all specimens examined. We demonstrate that previous studies misidentified graphene/graphane-oxide aggregates as hexagonal diamond and likely misidentified graphene as cubic diamond. Our results cast doubt upon one of the last widely discussed pieces of evidence supporting the YD impact hypothesis.archaeology | paleoclimate | Quaternary extinctions | carbon spherules | fungal sclerotia

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

“…Daulton et al (2010) found no YDB NDs and concluded that their findings cast doubt on the presence of YDB NDs, although they pointed out that YDB NDs might "occur inhomogeneously and only in some of the YD-boundary carbons and hence are not observed in our study" (p. 16046). Daulton et al (2010) also noted that other minerals, including nanocrystalline copper and copper oxide, could be misidentified as several of the proposed diamond polytypes, because of crystallographic similarities between copper and diamond.…”

“…Israde-Alcá ntara et al (2012b) used multiple analytical techniques to demonstrate that the YDB NDs from Lake Cuitzeo, Mexico, are cubic NDs, n-diamonds, i-carbon, and lonsdaleite-like crystals. Israde-Alcá ntara et al (2012b) also identified several problems and limitations of the study by Daulton et al (2010), who reported an absence of YDB NDs in carbon spherules at Murray Springs and Arlington Canyon. First, Daulton et al (2010) searched for and failed to find NDs within carbon spherules at Murray Springs, but neither Firestone et al (2007) nor Kennett et al (2009a) reported finding carbon spherules at that site, making the related absence of NDs unsurprising.…”

“…Israde-Alcá ntara et al (2012b) also identified several problems and limitations of the study by Daulton et al (2010), who reported an absence of YDB NDs in carbon spherules at Murray Springs and Arlington Canyon. First, Daulton et al (2010) searched for and failed to find NDs within carbon spherules at Murray Springs, but neither Firestone et al (2007) nor Kennett et al (2009a) reported finding carbon spherules at that site, making the related absence of NDs unsurprising. Our investigations showed that carbon spherules are most common in regions having conifer trees at 12,800 cal BP, not in scrubby grasslands, as existed at Murray Springs at that time (Haynes and Huckell 2007).…”

“…Following the identification of NDs by Kennett et al (2009aKennett et al ( , 2009b, Daulton et al (2010) attempted to replicate that discovery at two wellknown archaeological sites, Murray Springs, Arizona, and Arlington Canyon, California. Daulton et al (2010) found no YDB NDs and concluded that their findings cast doubt on the presence of YDB NDs, although they pointed out that YDB NDs might "occur inhomogeneously and only in some of the YD-boundary carbons and hence are not observed in our study" (p. 16046).…”

Late Quaternary sea-level history and the antiquity of mammoths (Mammuthus exilisandMammuthus columbi), Channel Islands National Park, California, USA

“…Other investigators have pointed out the possibility of a combination of human-caused and climate-related causes of extinction (see discussion in Barnosky et al, 2004). Although all three mechanisms are controversial, the extraterrestrial impact hypothesis has received a significant amount of criticism (e.g., Daulton et al, 2010;Pinter et al, 1998Pinter et al, , 2011Holliday et al, 2014;Meltzer et al, 2014) and is not considered further here. No attempt is made to discuss the pros and cons of the human vs. climate change causes for megafaunal extinction in North America, but some of the findings presented here have relevance to the debate on these two causes for mammoth extinction specifically on the Channel Islands.…”