James P. Kennett

Anomalous peak abundances of platinum and Fe-rich microspherules with high-temperature minerals have previously been demonstrated to be a chronostratigraphic marker for the lower Younger Dryas Boundary (YDB) dating to 12.8 ka. This study used Bayesian analyses to test this hypothesis in multiple sequences (units) of sandy, weakly stratified sediments at Wakulla Springs, Florida. Our investigations included platinum geochemistry, granulometry, optically stimulated luminescence (OSL) dating, and culturally dated lithics. In addition, sediments were analyzed using scanning electron microscopy and energy dispersive x-ray spectroscopy to investigate dendritic, iron-rich microspherules previously identified elsewhere in peak abundances at the onset of the Younger Dryas (YD) cool climatic episode. Our work has revealed this abundance peak in platinum and dendritic spherules in five sediment sequences at …

The original version of this Article inaccurately described the work of Dr Mark Boslough presented in Figure 53, by suggesting that the simulation presented in this figure is of the Tunguska event. However, the simulated event was much larger in force than the Tunguska event. The discussion and legend of Figure 53 were revised as follows to reflect this.

BERNHARD, JOAN, US BOWSER, SAMUEL, US BRENCKLE, PAUL, US BRUNNER, CHARLOTTE, US CHRISTENSEN, BETH, US COLLINS, LAUREL, US CULVER, STEPHEN, US FINGER, KENNETH, US GOLDSTEIN, SUSAN, US HALLOCK MULLER, PAMELA, US HOLBOURN, ANN, Germany HUBER, BRIAN, US ISHMAN, SCOTT, US JORISSEN, FRANS, France KAMINSKI, MICHAEL, Saudi Arabia KENNETT, JAMES, US KOHL, BARRY, US KUHNT, WOLFGANG, Germany LECKIE, R. MARK, US LEON-RODRIGUEZ, LIZETTE, US LIPPS, JERE, US

At Abu Hureyra, a well-studied archeological site in Syria, the onset boundary of the Younger Dryas climatic episode ~12,800 years ago has previously been proposed to contain evidence supporting a near-surface cosmic airburst impact that generated temperatures >2000°C. Here, we present a wide range of potential impact-related proxies representing the catastrophic effects of this cosmic impact that destroyed the village. These proxies include nanodiamonds (cubic diamonds, n-diamonds, i-carbon, and lonsdaleite-like crystals); silica-rich and iron-rich micro-spherules; and melted chromite, quartz, and zircon grains. Another proxy, meltglass, at a concentration of 1.6 wt% of bulk sediment, appears to have formed from terrestrial sediments and was found to partially coat toolmaking debitage, bones, and clay building plaster, suggesting that village life was adversely affected. Abundant meltglass fragments examined display remarkably detailed imprints of plant structures, including those of reeds. The nanodiamonds are proposed to have formed under anoxic conditions from the incineration of plant materials during high-temperature, impact-related fires, while geochemical evidence indicates that the micro-spherules formed from the melting of terrestrial sediments. Broad archeological and geochemical evidence supports the hypothesis that Abu Hureyra is the oldest known archeological site catastrophically destroyed by cosmic impact, thus revealing the potential dangers of such events.

This study investigates the hypothesis that Earth collided with fragments of a disintegrating comet, triggering Younger Dryas climate change 12,800 years ago. This collision created environmental conditions at Abu Hureyra, Syria, that favored the earliest known continuous cultivation of domestic-type grains and legumes, along with animal management, adding to the pre-existing practice of hunting-and-gathering. The proposed airburst coincided with a significant decline in local populations and led to architectural reorganizations of the village. These events immediately followed the deposition of the Younger Dryas Boundary layer that contains peak concentrations of high-temperature meltglass, nanodiamonds, platinum, and iridium. These proxies provide evidence of a nearby low-altitude airburst by a comet-like fragment of a former Centaur, one of many <300-km-wide bodies in unstable orbits between the giant planets. This large body is proposed to have undergone cascading disintegrations, thus producing the Taurid Complex containing Comet Encke and ~90 asteroids with diameters of ~1.5 to 5 km. Here, we present substantial new quantitative evidence and interpretations supporting the hypothesis that comet fragments triggered near-global shifts in climate ~12,800 years ago, and one airburst destroyed the Abu Hureyra village. This evidence implies a causative link between extraterrestrial airbursts, environmental change, and transformative shifts in human societies.

A previous investigation revealed that shock-fracturing, a form of low-pressure shock metamorphism in quartz grains, can be produced during near-surface atomic airbursts and in cosmic impact structures, most likely at pressures lower than 8 GPa. This discovery implies that similar shock-fracturing may also form in quartz grains exposed to near-surface airbursts by comets and asteroids. Here, we investigate this hypothesis by examining quartz grains in a sedimentary profile from Abu Hureyra, a prehistoric archaeological site in northern Syria. This site was previously proposed to have experienced a nearby, low-altitude cosmic airburst at the onset of the Younger Dryas (~12,800 years ago). The Younger Dryas boundary layer (YDB) at Abu Hureyra has previously been shown to contain a rich assemblage of materials consistent in indicating a cosmic impact. These include anomalously high concentrations of melted micro-spherules displaying increased remanent magnetism; meltglass with low water content indicative of high-temperature melting; nanodiamonds, potentially including lonsdaleite; carbon spherules produced by biomass burning; black carbon or soot; total organic carbon; and abnormally high-temperature melted refractory minerals and elements, including platinum, iridium, chromite, and zircon. To further test this impact hypothesis, we searched for evidence of shocked quartz, a robust, widely accepted indicator of cosmic impacts. We used a comprehensive analytical suite of high-resolution techniques, including …

Many studies of hypervelocity impact craters have described the characteristics of quartz grains shock-metamorphosed at high pressures of >10 GPa. In contrast, few studies have investigated shock metamorphism at lower shock pressures. In this study, we test the hypothesis that low-pressure shock metamorphism occurs in near-surface nuclear airbursts and that this process shares essential characteristics with crater-forming impact events. To investigate low-grade shock microstructures, we compared quartz grains from Meteor Crater, a 1.2-km-wide impact crater, to those from near-surface nuclear airbursts at the Alamogordo Bombing Range, New Mexico in 1945 and Kazakhstan in 1949/1953. This investigation utilized a comprehensive analytical suite of high-resolution techniques, including transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). Meteor Crater and the nuclear test sites all exhibit quartz grains with closely spaced, sub-micron-wide fractures that appear to have formed at low shock pressures. Significantly, these micro-fractures are closely associated with Dauphiné twins and are filled with amorphous silica (glass), widely considered a classic indicator of shock metamorphism. Thus, this study confirms that glass-filled shock fractures in quartz form during near-surface nuclear airbursts, as well as crater-forming impact events, and by extension, it suggests that they may form in any near-surface cosmic airbursts in which the shockwave is coupled to Earth’s surface, as has been …

We present evidence that in~ 1650 BCE (~ 3600 years ago), a cosmic airburst destroyed Tall el-Hammam, a Middle-Bronze-Age city in the southern Jordan Valley northeast of the Dead Sea. The proposed airburst was larger than the 1908 explosion over Tunguska, Russia, where a~ 50-m-wide bolide detonated with~ 1000× more energy than the Hiroshima atomic bomb. A city-wide~ 1.5-m-thick carbon-and-ash-rich destruction layer contains peak concentrations of shocked quartz (~ 5–10 GPa); melted pottery and mudbricks; diamond-like carbon; soot; Fe-and Si-rich spherules; CaCO 3 spherules from melted plaster; and melted platinum, iridium, nickel, gold, silver, zircon, chromite, and quartz. Heating experiments indicate temperatures exceeded 2000 C. Amid city-side devastation, the airburst demolished 12+ m of the 4-to-5-story palace complex and the massive 4-m-thick mudbrick rampart, while causing extreme …

A Tunguska Sized Airburst Destroyed Tall el‑Hammam a Middle Bronze Age City in the Jordan Valley Near the Dead Sea Find People Campus Map PiratePort AZ Toggle navigation About Submit Browse Login View Item ScholarShip Home ECU Main Campus Thomas Harriot College of Arts and Sciences Geological Sciences View Item ScholarShip Home ECU Main Campus Thomas Harriot College of Arts and Sciences Geological Sciences View Item Search The ScholarShip This Collection Browse All of The ScholarShipCommunities & CollectionsDateAuthorsTitlesSubjectsTypeDate SubmittedThis CollectionDateAuthorsTitlesSubjectsTypeDate Submitted My Account Login Statistics View Google Analytics Statistics A Tunguska Sized Airburst Destroyed Tall el‑Hammam a Middle Bronze Age City in the Jordan Valley Near the Dead Sea Thumbnail View/ Open …

At Abu Hureyra (AH), Syria, the 12,800-year-old Younger Dryas boundary layer (YDB) contains peak abundances in meltglass, nanodiamonds, microspherules, and charcoal. AH meltglass comprises 1.6 wt.% of bulk sediment, and crossed polarizers indicate that the meltglass is isotropic. High YDB concentrations of iridium, platinum, nickel, and cobalt suggest mixing of melted local sediment with small quantities of meteoritic material. Approximately 40% of AH glass display carbon-infused, siliceous plant imprints that laboratory experiments show formed at a minimum of 1200°–1300 °C; however, reflectance-inferred temperatures for the encapsulated carbon were lower by up to 1000 °C. Alternately, melted grains of quartz, chromferide, and magnetite in AH glass suggest exposure to minimum temperatures of 1720 °C ranging to >2200 °C. This argues against formation of AH meltglass in thatched hut fires at …

Teller et al.(2019) present radiocarbon analyses and paleoenvironmental data for a stratigraphic section at Lake Hind, Manitoba, Canada. The article expands on previous ones (Firestone et al., 2007; Kennett et al., 2015) arguing that extraterrestrial impact proxies are present at Lake Hind, comprising a Younger Dryas Boundary layer (YDB), and that this layer is synchronous with similar layers at other sites. However, we note three significant problems that cast doubt on their conclusions.First, there are inconsistencies in the reporting of radiocarbon dates purported to be associated with the YDB. Teller et al.(2019) state that middle Subunit B1 corresponds to the deposition of YDB impact proxies. They further report that this layer yielded “one calibrated radiocarbon age of 12,630±78 cal yr BP (PSUAMS-88701, 10,470±35 14C yr BP)”(Teller et al., 2019, p. 68)(we believe that sample PSUAMS-88701 was intended to …

Abstract HIGH-TEMPERATURE MELTING AT > 2200 C PROVIDES EVIDENCE OF COSMIC IMPACT AT ABU HUREYRA, SYRIA AT THE YOUNGER DRYAS ONSET (~ 12.8 KA). In AH glass, high formation temperatures followed by rapid cooling created oxygen-deficient minerals, such as native iron, native silicon, and alloys of Fe Cr, Au, and Al. HIGH-TEMPERATURE MELTING AT > 2200 C PROVIDES EVIDENCE OF COSMIC IMPACT AT ABU HUREYRA, SYRIA AT THE YOUNGER DRYAS ONSET (~ 12.8 KA).[Extracted from the article]Copyright of LPI Contribution is the property of Lunar & Planetary Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users …

: Natural marine hydrocarbon seeps on continental margins today represent a small source of methane in the global atmosphere budget, which is dominated by anthropogenic sources and contributions from wetlands in the tropics and northern high latitudes. In glacial times with lowered sea level, exposed seeps must have vented directly to the atmosphere and the portion of methane that was formerly dissolved and oxidized in the ocean contributed to the global atmospheric methane budget. We estimate that during lowered sea level 40-100× 1012 g/yr of methane were added to the atmosphere from gas seeps on the exposed shelves. This source could account for much of the atmospheric methane during glacial episodes because major wetlands were largely absent prior to the Holocene.© 2005 Elsevier Ltd. All rights reserved.

Deep-sea drilling in the Antarctic region (DSDP Legs 28, 29, 35 and 36) has provided much new data about the development of circum-Antarctic circulation through the Cainozoic. The development of this circulation has had profound effects on the total global oceanic circulation and climatic change. During the Palaeocene (t = ∼ 65 to 55 MY ago), Australia and Antarctica were joined. In the Early Eocene (t = ∼ 55 MY ago), Australia began to drift northwards from Antarctica forming an ocean, although circum-Antarctic flow was blocked by the continental South Tasman Rise and Tasmania. During the Eocene (t = 55 to 38 MY ago) the Southern Ocean was relatively warm and the continent largely non-glaciated. Cool temperate vegetation existed in some regions. By the Late Eocene (t = ∼ 39 MY ago) a shallow water connection had developed between the southern Indian and Pacific Oceans over the South …