YOUNGER DYRYAS (yd) Abstracts/Papers
by: Charles O’Dale
Extraordinary Biomass-Burning Episode and Impact Winter Triggered by the Younger Dryas Cosmic Impact ∼12,800 Years Ago. 1. Ice Cores and Glaciers
Wendy S. Wolbach et al
The Younger Dryas boundary (YDB) cosmic-impact hypothesis is based on considerable evidence that Earth collided with fragments of a disintegrating ≥100-km-diameter comet, the remnants of which persist within the inner solar system ∼12,800 y later. Evidence suggests that the YDB cosmic impact triggered an “impact winter” and the subsequent Younger Dryas (YD) climate episode, biomass burning, late Pleistocene megafaunal extinctions, and human cultural shifts and population declines. The cosmic impact deposited anomalously high concentrations of platinum over much of the Northern Hemisphere, as recorded at 26 YDB sites at the YD onset, including the Greenland Ice Sheet Project 2 ice core, in which platinum deposition spans ∼21 y (∼12,836–12,815 cal BP). The YD onset also exhibits increased dust concentrations, synchronous with the onset of a remarkably high peak in ammonium, a biomass-burning aerosol. In four ice-core sequences from Greenland, Antarctica, and Russia, similar anomalous peaks in other combustion aerosols occur, including nitrate, oxalate, acetate, and formate, reflecting one of the largest biomass-burning episodes in more than 120,000 y. In support of widespread wildfires, the perturbations in CO2 records from Taylor Glacier, Antarctica, suggest that biomass burning at the YD onset may have consumed ∼10 million km2, or ∼9% of Earth’s terrestrial biomass. The ice record is consistent with YDB impact theory that extensive impact-related biomass burning triggered the abrupt onset of an impact winter, which led, through climatic feedbacks, to the anomalous YD climate episode. (Journal of Geology Feb 01, 2018)
Part 1 of this study investigated evidence of biomass burning in global ice records, and here we continue to test the hypothesis that an impact event at the Younger Dryas boundary (YDB) caused an anomalously intense episode of biomass burning at ∼12.8 ka on a multicontinental scale (North and South America, Europe, and Asia). Quantitative analyses of charcoal and soot records from 152 lakes, marine cores, and terrestrial sequences reveal a major peak in biomass burning at the Younger Dryas (YD) onset that appears to be the highest during the latest Quaternary. For the Cretaceous-Tertiary boundary (K-Pg) impact event, concentrations of soot were previously utilized to estimate the global amount of biomass burned, and similar measurements suggest that wildfires at the YD onset rapidly consumed ∼10 million km2 of Earth’s surface, or ∼9% of Earth’s biomass, considerably more than for the K-Pg impact. Bayesian analyses and age regressions demonstrate that ages for YDB peaks in charcoal and soot across four continents are synchronous with the ages of an abundance peak in platinum in the Greenland Ice Sheet Project 2 (GISP2) ice core and of the YDB impact event (12,835–12,735 cal BP). Thus, existing evidence indicates that the YDB impact event caused an anomalously large episode of biomass burning, resulting in extensive atmospheric soot/dust loading that triggered an “impact winter.” This, in turn, triggered abrupt YD cooling and other climate changes, reinforced by climatic feedback mechanisms, including Arctic sea ice expansion, rerouting of North American continental runoff, and subsequent ocean circulation changes. (Journal of Geology Feb 01, 2018)
Nanodiamond-Rich Layer across Three Continents Consistent with Major Cosmic Impact at 12,800 Cal BP
ABSTRACT A major cosmic-impact event has been proposed at the onset of the Younger Dryas (YD) cooling episode at ≈12,800 ±150 years before present, forming the YD Boundary (YDB) layer, distributed over 150 million km2 on four continents. In 24 dated stratigraphic sections in 10 countries of the Northern Hemisphere, the YDB layer contains a clearly defined abundance peak in nanodiamonds (NDs), a major cosmic-impact proxy. Observed ND polytypes include cubic diamonds, lonsdaleite-like crystals, and diamond-like carbon nanoparticles, called n-diamond and i-carbon. The ND abundances in bulk YDB sediments ranged up to ≈500 ppb (mean: 200 ppb) and that in carbon spherules up to ≈3700 ppb (mean: ≈750 ppb); 138 of 205 sediment samples (67%) contained no detectable NDs. Isotopic evidence indicates that YDB NDs were produced from terrestrial carbon, as with other impact diamonds, and were not derived from the impactor itself. The YDB layer is also marked by abundance peaks in other impact-related proxies, including cosmic-impact spherules, carbon spherules (some containing NDs), iridium, osmium, platinum, charcoal, aciniform carbon (soot), and high-temperature melt-glass. This contribution reviews the debate about the presence, abundance, and origin of the concentration peak in YDB NDs. We describe an updated protocol for the extraction and concentration of NDs from sediment, carbon spherules, and ice, and we describe the basis for identification and classification of YDB ND polytypes, using nine analytical approaches. The large body of evidence now obtained about YDB NDs is strongly consistent with an origin by cosmic impact at ≈12,800 cal BP and is inconsistent with formation of YDB NDs by natural terrestrial processes, including wildfires, anthropogenesis, and/or influx of cosmic dust. (Kinzie et al, 2014)
Nanosecond formation of diamond and lonsdaleite by shock compression of graphite
The shock-induced transition from graphite to diamond has been of great scientific and technological interest since the discovery of microscopic diamonds in remnants of explosively driven graphite. Furthermore, shock synthesis of diamond and lonsdaleite, a speculative hexagonal carbon polymorph with unique hardness, is expected to happen during violent meteor impacts. Here, we show unprecedented in situ X-ray diffraction measurements of diamond formation on nanosecond timescales by shock compression of pyrolytic as well as polycrystalline graphite to pressures from 19 GPa up to 228 GPa. While we observe the transition to diamond starting at 50 GPa for both pyrolytic and polycrystalline graphite, we also record the direct formation of lonsdaleite above 170 GPa for pyrolytic samples only. Our experiment provides new insights into the processes of the shock-induced transition from graphite to diamond and uniquely resolves the dynamics that explain the main natural occurrence of the lonsdaleite crystal structure being close to meteor impact sites. (Kraus et al 2016)
The origin of the Carolina Bays presents a formidable puzzle for geologists and astronomers. The elliptical bays with sandy rims look like they were made by huge impacts, but they do not have the characteristic markers associated with extraterrestrial impacts. The dates of the terrain on which the bays are found span millennia, forcing scientists to conclude that the bays must have been made by the action of wind and water over the last 140,000 years. A new geometrical survey has found that the Carolina Bays are perfect ellipses with similar width-to-length ratios as the Nebraska rainwater basins. This book starts from the premise that if the Carolina Bays are conic sections, they must have originated from oblique conical cavities that were transformed by geological processes to their current form. Mathematical analysis following this line of reasoning provides clues supporting the idea that the Earth was hit during the ice age by an extraterrestrial object. The impact may have triggered the Younger Dryas cold event and caused the extinction of the North American megafauna and the Clovis culture. The Carolina Bays are the remodeled remains of oblique conical craters formed on ground liquefied by secondary impacts of glacier ice boulders ejected from the primary impact site.(Zamora 2016)
The Younger Dryas impact hypothesis: A requiem
The Younger Dryas (YD) impact hypothesis is a recent theory that suggests that a cometary or meteoritic body or bodies hit and/or exploded over North America 12,900 years ago, causing the YD climate episode, extinction of Pleistocene megafauna, demise of the Clovis archeological culture, and a range of other effects. Since gaining widespread attention in 2007, substantial research has focused on testing the 12 main signatures presented as evidence of a catastrophic extraterrestrial event 12,900 years ago. Here we present a review of the impact hypothesis, including its evolution and current variants, and of efforts to test and corroborate the hypothesis.
The physical evidence interpreted as signatures of an impact event can be separated into two groups. The first group consists of evidence that has been largely rejected by the scientific community and is no longer in widespread discussion, including: particle tracks in archeological chert; magnetic nodules in Pleistocene bones; impact origin of the Carolina Bays; and elevated concentrations of radioactivity, iridium, and fullerenes enriched in 3He. The second group consists of evidence that has been active in recent research and discussions: carbon spheres and elongates, magnetic grains and magnetic spherules, byproducts of catastrophic wildfire, and nanodiamonds. Over time, however, these signatures have also seen contrary evidence rather than support. Recent studies have shown that carbon spheres and elongates do not represent extraterrestrial carbon nor impact-induced megafires, but are indistinguishable from fungal sclerotia and arthropod fecal material that are a small but common component of many terrestrial deposits. Magnetic grains and spherules are heterogeneously distributed in sediments, but reported measurements of unique peaks in concentrations at the YD onset have yet to be reproduced. The magnetic grains are certainly just iron-rich detrital grains, whereas reported YD magnetic spherules are consistent with the diffuse, non-catastrophic input of micrometeorite ablation fallout, probably augmented by anthropogenic and other terrestrial spherular grains. Results here also show considerable subjectivity in the reported sampling methods that may explain the purported YD spherule concentration peaks. Fire is a pervasive earth-surface process, and reanalyses of the original YD sites and of coeval records show episodic fire on the landscape through the latest Pleistocene, with no unique fire event at the onset of the YD. Lastly, with YD impact proponents increasingly retreating to nanodiamonds (cubic, hexagonal [lonsdaleite], and the proposed n-diamond) as evidence of impact, those data have been called into question. The presence of lonsdaleite was reported as proof of impact-related shock processes, but the evidence presented was inconsistent with lonsdaleite and consistent instead with polycrystalline aggregates of graphene and graphane mixtures that are ubiquitous in carbon forms isolated from sediments ranging from modern to pre-YD age. Important questions remain regarding the origins and distribution of other diamond forms (e.g., cubic nanodiamonds).
In summary, none of the original YD impact signatures have been subsequently corroborated by independent tests. Of the 12 original lines of evidence, seven have so far proven to be non-reproducible. The remaining signatures instead seem to represent either (1) non-catastrophic mechanisms, and/or (2) terrestrial rather than extraterrestrial or impact-related sources. In all of these cases, sparse but ubiquitous materials seem to have been misreported and misinterpreted as singular peaks at the onset of the YD. Throughout the arc of this hypothesis, recognized and expected impact markers were not found, leading to proposed YD impactors and impact processes that were novel, self-contradictory, rapidly changing, and sometimes defying the laws of physics. The YD impact hypothesis provides a cautionary tale for researchers, the scientific community, the press, and the broader public. (Pinter et al 2011)
Comprehensive analysis of nanodiamond evidence relating to the Younger Dryas Impact Hypothesis
19 December 2016
Tyrone L. Daulton, Sachiko Amari, Andrew C. Scott, Mark Hardiman, Nicholas Pinter, R. Scott Anderson
During the end of the last glacial period in the Northern Hemisphere near 12.9k cal a BP, deglacial warming of the Bølling–Ållerod interstadial ceased abruptly and the climate returned to glacial conditions for an interval of about 1300 years known as the Younger Dryas stadial. The Younger Dryas Impact Hypothesis proposes that the onset of the Younger Dryas climate reversal, Pleistocene megafaunal extinctions and disappearance of the Clovis paleoindian lithic technology were coeval and caused by continent-wide catastrophic effects of impact/bolide events in North America. While there are no known impact structures dated to the Younger Dryas onset, physical evidence of the impact/bolide events is argued to be present in sediments spanning several continents at stratigraphic levels inferred to date to the Bølling-Ållerod/Younger Dryas boundary (YDB). Reports of nanometer to submicron-sized diamonds in YDB sediments, in particular the rare 2H hexagonal polytype of diamond, lonsdaleite, have been presented as strong evidence for shock processing of crustal materials. We review the available data on diamonds in sediments and provide new data. We find no evidence for lonsdaleite in YDB sediments and find no evidence of a spike in nanodiamond concentration at the YDB layer to support the impact hypothesis.
Palaeolithic extinctions and the Taurid Complex