Background Previous work identified a platinum anomaly at Wonderkrater, South Africa, within sediments modeled to the onset of the Younger Dryas (~12,800 cal BP). To investigate the nature of this anomaly, we analyzed sedimentary nanoparticles using single-particle inductively coupled plasma time-of-flight mass spectrometry (SP-ICP-TOF-MS). Methods Nanoparticles were extracted from peat sediments spanning the modeled Younger Dryas Boundary (YDB) interval and analyzed for particle number concentrations, elemental compositions, elemental ratios, and multi-element nanoparticle clusters. Results from the YDB interval were compared with sediments above and below the anomaly. Results A pronounced geochemical anomaly is confined to a narrow interval between 357.5 and 362.5 cm depth. Total nanoparticle number concentrations increase by a factor of 4.6 relative to surrounding sediments (p < 0.01), accompanied by reduced average particle mass. The anomalous interval contains two distinct nanoparticle populations: one enriched in platinum-group and siderophile elements, and a second enriched in lithophile and rare earth elements. Eight elemental ratios exhibit elevated values relative to background sediments, including Au/Ir (3.80), Cr/Ni (3.75), and Au/Pt (1.16), each exceeding background values by more than a factor of two. Systematic fractionation among noble and siderophile elements is also evident, with Au, Pt, and Pd exhibiting greater enrichments than Os, Ir, and Ru, consistent with elemental fractionation during high-temperature vaporization, condensation, and atmospheric transport processes. Several multi-element nanoparticle clusters occur predominantly within the YDB interval. Conclusions The YDB layer at Wonderkrater contains a compositionally distinct nanoparticle assemblage characterized by elevated platinum-group elements, siderophile-element enrichments, unique elemental ratios, and changes in terrestrial dust-related signatures. The elemental ratio patterns and nanoparticle populations are consistent with a compositionally heterogeneous, volatile-bearing extraterrestrial component modified by high-temperature processes, together with enhanced terrestrial dust input. These observations are consistent with the introduction of geochemically distinct nanoparticle populations coincident with the onset of the Younger Dryas.

Geoarchaeological investigations at site 44PY152 near Smith Mountain Lake, Virginia, document stratified Late Pleistocene–Early Holocene archaeological occupations preserved within ~1.7 m of floodplain alluvium. These deposits contain both in situ and eroding fluted Paleoamerican and Early Archaic projectile points. Here, we analyze a contiguous, high-resolution sedimentary sequence to evaluate the presence and stratigraphic integrity of microspherule and platinum-group element (PGE) anomalies associated with the onset of the Younger Dryas (YD). Analyses include Bayesian radiocarbon modeling, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS), single-particle inductively coupled plasma time-of-flight mass spectrometry (SP-ICP-TOF-MS), laser ablation ICP-MS (LA-ICP-MS), laser granulometry, bulk organic carbon and nitrogen, soot carbon, stable carbon isotopes (δ 13 C_OC and δ 13 C_soot), magnetic susceptibility, and mercury (Hg). Results reveal a narrow microspherule-rich interval centered within the 14–15 cmbd sample that is accompanied by pronounced PGE mass anomalies consistent with proxy assemblages reported near the Younger Dryas Boundary at multiple sites worldwide. Bayesian age modeling places this interval within the broader temporal range of the Younger Dryas onset, although the modeled age uncertainty exceeds the narrower age range proposed by Kennett et al. [ 1 ]. Chondrite-normalized elemental systematics indicate selective Pt-centered enrichment decoupled from comparatively conservative rare earth element behavior, arguing against simple sedimentological concentration processes. The stratigraphic position and internal coherence of this proxy suite identify a discrete marker horizon consistent with the onset of the Younger Dryas at 44PY152. Subtle excursions in δ 13 C_soot and Hg immediately above this interval may reflect associated environmental variability during the early Younger Dryas. Regardless of formation mechanism, the microspherule–PGE horizon provides a high-resolution stratigraphic marker confined to a 1-cm interval that may aid correlation and interpretation of pre- and post-12.8 ka archaeological sequences at stratified sites lacking abundant chronometric control.

The relationship between the Laacher See eruption, the Younger Dryas Boundary (YDB) layer, and the abrupt onset of Younger Dryas (YD) climate change remains uncertain. The Körslättamossen fen in southernmost Sweden provides the first robustly dated Scandinavian record in which these events are clearly separated stratigraphically. The LST layer at 288.5 cm (~13,006 cal BP) lies 6–10 cm below a discrete PGE-rich horizon (282–279 cm) marking YDB deposition, interpreted here as a 3-cm-thick fallout layer, with a Bayesian-modeled age of 12,861 ± 54 cal BP, ~150 years after the eruption, indicating that the Laacher See eruption and YDB deposition represent stratigraphically separate events. Within this fallout layer, Fe–Si microspherules with dendritic quench textures peak at 282–281 cm, while maximum PGE-bearing nanoparticle mass occurs at 280–279 cm, consistent with delayed settling of submicron particles. LA-ICP-MS reveals Si-rich microspherules containing PGE-bearing microdomains but negligible Ni, Co, and Cr. These compositions differ from both typical meteoritic metal and Laacher See volcanic glass, indicating that neither meteoritic metal ablation nor local volcanism provides a likely primary source for the microspherules. Single-particle ICP-TOF-MS detects a sharp Pt anomaly with Pt-dominant elemental ratios (e.g., high Pt relative to Fe and Ir), consistent with the platinum enrichment reported in the GISP2 ice core at the Younger Dryas Boundary. Immediately above the fallout layer, a dark, organic-rich horizon records the abrupt hydroclimatic shift to cooler, wetter YD conditions. These observations document three stratigraphically distinct events: the Laacher See eruption, a separate YDB fallout layer, and the near-synchronous onset of Younger Dryas climate change, providing a well-constrained European stratigraphic framework for evaluating mechanisms proposed for the Younger Dryas onset.

The Younger Dryas Boundary (YDB), dated to ~12.8 ka, marks the onset of an abrupt return to near-glacial conditions across much of the Northern Hemisphere. Numerous terrestrial sites contain unusual assemblages of high-temperature materials and geochemical anomalies near this boundary, but marine records remain comparatively sparse. Here we report a multiproxy investigation of four sediment cores (52, 64, 67, and 77) from Baffin Bay, a climatically sensitive region adjacent to the Laurentide Ice Sheet and downstream of major North Atlantic circulation pathways. Within glaciogenic marine sediments dated to the YD onset, we identify distinct layers enriched in inferred impact-related proxies, including meltglass, spherules, carbonaceous particles, metallic dust particles, cometary dust particles, and platinum-group element (PGE) anomalies. Nanoparticles (<1 μm) extracted from bulk sediments were analyzed using single-particle inductively coupled plasma time-of-flight mass spectrometry (SP-ICP-TOF-MS), allowing determination of elemental masses and ratios within individual particles. Concentrations of Pt, Ir, Ni, and Co show pronounced peaks associated with the YDB interval across all cores. Elemental mass ratios within nanoparticles, including Ir/Pt, Pt/Pd, Pt/Fe, Co/Ni, and Ni/Fe, also increase sharply within the same stratigraphic interval, with maxima typically occurring slightly above peaks in microspherules and carbonaceous particles. The diagnostic ratio of Pt/Fe is most similar to that of metal-rich extraterrestrial compositions, including comets, and is also strongly enriched relative to average crustal material. The stratigraphic coherence of these enrichments across cores spanning shelf to deep-basin environments indicates a basin-wide depositional signal rather than localized sedimentary processes. The slight offset between peaks in larger melted spherules and submicron nanoparticles is consistent with delayed atmospheric fallout of fine material and subsequent settling through the water column, potentially enhanced by aggregation into marine snow. Background nanoparticle abundances outside the YDB interval are comparatively low, suggesting that the observed enrichments represent a short-lived pulse of metal-rich particulate input. Taken together, the multiproxy evidence from Baffin Bay supports the presence of an unusual depositional layer at the onset of the Younger Dryas marked by high-temperature materials and PGE-enriched nanoparticles. While these anomalies and individual proxies may have alternative explanations, their co-occurrence, stratigraphic confinement, and replication across multiple, widely separated marine cores argue for a common origin. The data are consistent with the addition of extraterrestrial material from a high-energy event capable of injecting large quantities of fine particulate matter into the atmosphere and ocean. Such an event could have contributed to rapid environmental perturbations at the Younger Dryas onset, including atmospheric dust loading and disruption of regional climate. These findings extend the geographic range of YDB proxies into the marine realm of Baffin Bay and provide independent evidence for a sudden, basin-wide depositional episode at ~12.8 ka.

To test two competing hypotheses for the Younger Dryas trigger (extraterrestrial impact versus volcanism), we analyzed a high-resolution multiproxy record from Hall’s Cave, Texas, which preserves a continuous sedimentary archive from the Last Glacial Maximum through the Holocene. A Bayesian age–depth model based on 61 radiocarbon dates places the Younger Dryas Boundary (YDB) at 12,780 ± 170 cal BP, coincident with abrupt cooling, aridification, and sharply reduced sedimentation. At this boundary, biotic indicators record major ecological disruption, including a collapse of megafaunal dung-fungus spores and declining species richness. Geochemical profiles (magnetic susceptibility, δ 15 N, C/N, Hg/TOC) document hydroclimatic change and show no pronounced Hg/TOC enrichment at the YDB, indicating no evidence for a significant Hg-rich volcanic input at Hall’s Cave. In contrast, the YDB layer contains multiple high-temperature and shock proxies, including melted microspherules, carbon spherules, soot, nanodiamonds, and shocked quartz, identified using SEM-EDS and TEM analyses. Single-particle ICP-TOF-MS detects enrichments in Ni–Fe, Co–Fe, Fe–Si, Al–Ir, and Ti–Ir nanoparticle associations, including element combinations characteristic of meteoritic material and high-temperature condensation. These proxies define a two-step sequence consisting of a condensed boundary layer containing high-temperature and high-pressure (shock metamorphism) materials, followed by an early Younger Dryas interval characterized by increased dust input consistent with regional aridification. Collectively, the chronological, geochemical, mineralogical, and faunal evidence indicates a high-temperature and high-pressure event at ~12.8 ka and supports an extraterrestrial airburst or impact as the most consistent explanation for the Younger Dryas Boundary, in agreement with the Younger Dryas Impact Hypothesis (YDIH).

Previously, a large platinum (Pt) anomaly was reported in the Greenland ice sheet at the Younger Dryas boundary (YDB) (12,800 Cal B.P.). In order to evaluate its geographic extent, fire-assay and inductively coupled plasma mass spectrometry (FA and ICP-MS) elemental analyses were performed on 11 widely separated archaeological bulk sedimentary sequences. We document discovery of a distinct Pt anomaly spread widely across North America and dating to the Younger Dryas (YD) onset. The apparent synchroneity of this widespread YDB Pt anomaly is consistent with Greenland Ice Sheet Project 2 (GISP2) data that indicated atmospheric input of platinum-rich dust. We expect the Pt anomaly to serve as a widely-distributed time marker horizon (datum) for identification and correlation of the onset of the YD climatic episode at 12,800 Cal B.P. This Pt datum will facilitate the dating and correlating of archaeological, paleontological, and paleoenvironmental data between sequences, especially those with limited age control.

Here, we present a multidisciplinary investigation of a late-Pleistocene Greenland ice-margin sequence near Kangerlussuaq that spans the Bølling-Allerød, Younger Dryas, and early Holocene. This study investigates the cause of the Younger Dryas (YD) cooling event (~12,800 years ago) and its possible relationship to a cosmic impact. The Kangerlussuaq interval was previously identified using visible dust stratigraphy, oxygen-isotope measurements, and a peak in nanocarbon particles interpreted as nanodiamonds. We expand that record using bulk ICP-MS, single-particle ICP-time-of-flight mass spectrometry (SP-ICP-TOF-MS), microscopy, mineralogical observations, and hydrocode modeling. The Kangerlussuaq sequence preserves a dark, dust-rich YD interval bounded by clearer Holocene and Bølling-Allerød ice. Stable δ 18 O values and dust-related geochemical changes support correlation of this interval with the YD cooling episode, although the ice-margin setting introduces uncertainties related to compression, ablation, meltwater infiltration, and multi-season sample alignment. Within this framework, the Greenland record resolves three superimposed signals. First, bulk geochemistry and nanoparticle mineral-phase associations document a sustained YD-scale reorganization of atmospheric dust provenance and transport, consistent with colder, drier, and windier conditions and enhanced mineral-dust flux throughout much of the ~1,200–1,300-year YD interval. Second, a narrow proxy-rich horizon at the YDB layer (~5.5 m along the sloping ice) contains peak abundances of multiple particulate proxies, including nanocarbon particles previously interpreted as nanodiamonds, quartz grains with shocked planar microstructures, meltglass, glass-filled lithic aggregates, Fe- and Si-rich spherules, carbon-rich spherules, glasslike carbon, charcoal, and soot. Third, nanoparticle concentrations begin to rise at the YDB layer (~5.5 m), marking the onset of enrichment, but reach their maximum immediately above, at ~5.2 m. SP-ICP-TOF-MS identifies this overlying interval as the peak in nanoparticle-scale terrestrial and siderophile components, including Nb, Ta, U, As, Pb, Sb, PGEs, Ni, Co, and Re. Elemental behavior across the nanoparticle dataset can be grouped into three principal populations: climate-driven terrestrial mineral dust, high-temperature plume-derived possible ET condensates, and lower-temperature terrestrial plume derivatives. This offset between the boundary layer and the nanoparticle maximum is a key observation: concentrations are lowest within the YDB layer, increase at the boundary, and peak in the overlying sample, indicating temporally structured deposition involving initial boundary-layer input followed by delayed fallout or redistribution of fine particles. This delay is supported by independent evidence from the GISP2 ice core of a platinum anomaly coincident with the onset of Younger Dryas climate change, including a delayed peak over ~21 years, supporting non-instantaneous deposition of impact-related material and suggesting a temporal link to YD climate change. The PGE-bearing nanoparticle population provides the strongest geochemical evidence for a non-crustal contribution. At ~5.2 m, PGE sum, Ir, Pt, Os, Pd, Ni, Co, and Re are enriched relative to the YDB layer; these elements are strongly enriched in extraterrestrial (ET) materials relative to crustal abundances, suggesting a non-terrestrial source. Ratio-ratio diagrams and PGE fractionation versus Ir/Fe comparisons indicate that the YDB nanoparticle population is compositionally distinct from Greenland background dust and typical terrestrial reservoirs. The Greenland YDB value of (Os+Ir+Ru)/(Rh+Pd+Pt) is sub-chondritic, while Ir/Fe is highly elevated, consistent with a heterogeneous mixture containing a refractory PGE-rich component, possibly from ET refractory metal nuggets (RMNs), together with more volatile PGE-bearing material. This signature does not match any single impactor class (e.g., bulk chondrite, iron meteorite, or achondrite), but is consistent with a mixed, fractionated nanoparticle population superimposed on background cosmic dust influx. Hydrocode modeling demonstrates that a high-velocity impact or airburst interacting with an ice-sheet target can plausibly generate high pressures, elevated temperatures, shocked quartz, melt products, spherules, and widespread nanoparticle dispersal; however, this modeling is intended to illustrate a viable mechanism for proxy formation and does not imply that such an impact occurred at the Greenland site. Instead, these results are consistent with broader Younger Dryas Impact Hypothesis scenarios involving regionally or globally distributed impact and airburst phenomena. The combined proxy assemblage is difficult to explain by volcanism, biomass burning, authigenesis, anthropogenic contamination, or climate-driven dust deposition alone. No single proxy is uniquely diagnostic of impact; rather, the interpretation rests on the stratigraphic co-occurrence of multiple high-temperature, shocked, carbonaceous, siderophile-enriched, and PGE-bearing materials within the YD onset interval. Together, the Greenland record is consistent with a short-duration, high-energy airburst or impact-related depositional episode superimposed on and possibly a major trigger of the broader climatic transition into the Younger Dryas.

The Younger Dryas Impact Hypothesis (YDIH) posits that ~12,800 years ago Earth encountered the debris stream of a disintegrating comet, triggering hemisphere-wide airbursts, atmospheric dust loading, and the deposition of a distinctive suite of extraterrestrial (ET) impact proxies at the Younger Dryas Boundary (YDB). Until now, evidence supporting this hypothesis has come only from terrestrial sediment and ice-core records. Here we report the first discovery of similar impact-related proxies in ocean sediments from four marine cores in Baffin Bay that span the YDB layer at water depths of 0.5-2.4 km, minimizing the potential for modern contamination. Using scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) and laser ablation ICP-MS, we detect synchronous abundance peaks of metallic debris geochemically consistent with cometary dust, co-occurring with iron- and silica-rich microspherules (4-163 μm) that are predominantly of terrestrial origin with minor (<2 wt%) ET contributions. These microspherules were likely formed by low-altitude touchdown airbursts and surface impacts of comet fragments and were widely dispersed. In addition, single-particle ICP-TOF-MS analysis reveals nanoparticles (<1 μm) enriched in platinum, iridium, nickel, and cobalt. Similar platinum-group element anomalies at the YDB have been documented at dozens of sites worldwide, strongly suggesting an ET source. Collectively, these findings provide robust support for the YDIH. The impact event likely triggered massive meltwater flooding, iceberg calving, and a temporary shutdown of thermohaline circulation, contributing to abrupt Younger Dryas cooling. Our identification of a YDB impact layer in deep marine sediments underscores the potential of oceanic records to broaden our understanding of this catastrophic event and its climatological impacts.

We present evidence that Tall el-Hammam, a fortified Middle Bronze Age city in the Jordan Valley, was destroyed by an extraordinary high-energy event in approximately 1650 BCE. Excavations reveal that more than 12 m of a palace complex and a massive mudbrick rampart were leveled, and widespread fatalities occurred, with all skeletal remains displaying significant disarticulation. The entire city is capped by a ~1.5 m-thick charcoal-and-ash-rich destruction layer containing shock-metamorphic and high-temperature materials. This stratum yields abundant shocked quartz, vesicular melted pottery and mudbrick, diamond-like carbon, soot, Fe- and Si-rich microspherules, and CaCO 3 spherules derived from melted plaster. SEM/TEM imaging with EDS and electron backscatter diffraction (EBSD) identified planar deformation features and high-pressure mineral phases diagnostic of shock metamorphism. Metallic micro-droplets of platinum, iridium, nickel, gold, silver, zircon, chromite, and quartz imply transient exposure to temperatures exceeding 2000°C. Scattered debris fields (potsherds, charred grain, charcoal, and bone fragments) exhibit a coherent southwest-to-northeast dispersal pattern consistent with a directed supersonic shock wave. Anomalously high salt concentrations (~4 wt%) in the destruction layer provide evidence for the vaporization of Dead Sea brines or sedimentary salts, producing hypersaline soils that appear to have inhibited agriculture. This environmental breakdown coincides with an enigmatic ~300–600-year regional abandonment of Tall el-Hammam and surrounding settlements in the lower Jordan River Valley. Some researchers suggest that an oral tradition of this catastrophe may have been preserved in the biblical narrative of the destruction of Sodom. The observed suite of shock, melt, and geochemical signatures cannot be explained by natural disasters, fires, earthquakes, lightning, anthropogenic activity, or warfare. We therefore propose a cosmic airburst by a comet or asteroid of “super-Tunguska” magnitude—several times larger than the 1908 Tunguska event. To test this hypothesis, we conducted hydrocode simulations of a Type-II “touchdown” airburst (an airburst whose fireball reaches Earth’s surface), reproducing a high-velocity, high-temperature jet impacting the surface and generating meltglass, microspherules, and multi-GPa shock metamorphism. The modeled results match the evidence observed at Tall el-Hammam. Collectively, the geological, geochemical, geophysical, and archaeological evidence converges on a super-Tunguska-scale airburst as the most likely mechanism for the city’s destruction. Although such events are rare (estimated global recurrence interval of 200 to 1000 years), their capacity to devastate entire urban areas highlights the need for modern recognition and mitigation of the hazards posed by high-energy cosmic airbursts.

Shocked quartz grains are an accepted indicator of crater-forming cosmic impact events, which also typically produce amorphous silica along the fractures. Furthermore, previous research has shown that shocked quartz can form when nuclear detonations, asteroids, and comets produce near-surface or "touch-down" airbursts. When cosmic airbursts detonate with enough energy and at sufficiently low altitude, the resultant relatively small, high-velocity fragments may strike Earth's surface with high enough pressures to generate thermal and mechanical shock that can fracture quartz grains and introduce molten silica into the fractures. Here, we report the discovery of shocked quartz grains in a layer dating to the Younger Dryas (YD) onset (12.8 ka) in three classic archaeological sequences in the Southwestern United States: Murray Springs, Arizona; Blackwater Draw, New Mexico; and Arlington Canyon, California. These sites were foundational in demonstrating that the extinction or observed population bottlenecks of many megafaunal species and the coeval collapse/reorganization of the Clovis technocomplex in North America co-occurred at or near the YD onset. Using a comprehensive suite of 10 analytical techniques, including electron microscopy (TEM, SEM, CL, and EBSD), we have identified grains with glass-filled fractures similar to shocked grains associated with nuclear explosions and 27 accepted impact craters of different ages (e.g., Meteor Crater, 50 ka; Chesapeake Bay, 35 Ma; Chicxulub, 66 Ma; Manicouagan, 214 Ma) and produced in 11 laboratory shock experiments. In addition, we used hydrocode modeling to explore the temperatures, pressures, and shockwave velocities associated with the airburst of a 100-m fragment of a comet and conclude that they are sufficient to produce shocked quartz. These shocked grains co-occur with previously reported peak concentrations in platinum, meltglass, soot, and nanodiamonds, along with microspherules, similar to those found in ~28 microspherule layers that are accepted as evidence for cosmic impact events, even in the absence of a known crater. The discovery of apparently thermally-altered shocked quartz grains at these three key archaeological sites supports a cosmic impact as a major contributing factor in the megafaunal extinctions and the collapse of the Clovis technocomplex at the YD onset.

Microfossils have been used extensively in the Baffin Bay region to reconstruct Late Pleistocene and Holocene paleoenvironmental/paleoceanographic conditions. The foraminifera of three northeast Baffin Bay slope/basin cores and a core from northern Baffin Bay at the mouth of Jones Sound have been documented to investigate paleoenvironmental changes across the Younger Dryas (YD) interval. Seventeen new foraminifera-based AMS C14 age estimates provide the temporal context. YD sediments in mid-slope cores 64 and 77 and basinal core 67 occur between two widely recognized intervals (BBDC 1 and BBDC 0) characterized by carbonate-rich, ice-rafted debris (IRD). These occurred late in the B & oslash;lling-Aller & oslash;d (BA) warm interval and during the immediately post-YD warming in the early Holocene, respectively. Despite containing this sedimentological signal, cores 64, 67 and 77 contain foraminiferal assemblages related to depth of water and associated water masses, and do not demonstrate a signal that can be definitively attributed to the Younger Dryas cold climatic event. In contrast, core 52, from a cross-shelf trough at the mouth of Jones Sound, does not exhibit the two distinctive IRD units. Presumably this is due to its location north of Lancaster Sound, the likely source of much IRD for Baffin Bay. It does, however, exhibit distinctive foraminiferal assemblages for the relatively warm BA, the cold YD, and the relatively warm early Holocene that can be attributed to environmental changes. These assemblages, however, are not diagnostic of the YD. Retreat of the ice margin into Jones Sound occurred by 14,354-13690 cal yr BP, earlier than previously indicated.

We report evidence of a likely low-altitude cosmic airburst near Perkins, Louisiana, associated with semi-consolidated deposits containing abundant shocked quartz grains, a classical impact indicator, along with spherules, meltglass, and microbreccia. Analytical techniques employed on these materials include optical microscopy, the universal stage, electron microscopy (SEM, TEM, and STEM), cathodoluminescence, laser ablation (LA-ICP-MS), neutron activation (INAA), and radiometric dating. These analyses reveal that the deposits exhibit morphological and compositional similarities to known impact-related proxies. Radiocarbon dating and 40Ar/39Ar analyses constrain the likely age of deposition to between 30,000 and 10,000 calibrated years BP, with a concentration of dates clustering around 12,800 years BP (12,835-12,735 cal BP), coinciding with the age range of the Younger Dryas Boundary (YDB). Spherule and meltglass abundances, along with evidence of high-temperature mineral transformations, are consistent with the effects of a high-energy airburst or impact. Hydrocode modeling suggests that a touch-down airburst could plausibly account for the observed shallow depression, material dispersal patterns, and geochemical signatures. Our study suggests that a 300-m-long lake/depression at the Perkins site represents North America’s first identified YDB-age airburst crater.

We report diverse shock-metamorphosed and melted grains from the 1908 airburst site in Russia, one of history’s most significant and enigmatic cosmic events. Analysis of samples from a rimmed crater-like feature near the epicenter using scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron backscatter diffraction (EBSD), and cathodoluminescence (CL) revealed evidence of extreme conditions. Our findings indicate heterogeneous shock pressures (~≥2 GPa) and temperatures (~≥1710°C) produced various microparticles, including FeO and aluminosilicate glass microspherules, melted quartz microspherules, carbon spherules, glass-like carbon, and melted minerals. Notably, quartz grains exhibit high-temperature melting and shock metamorphism, including planar deformation features (PDFs) and planar fractures (PFs), with some showing glass-lined internal fractures and melted silica coatings. Similarly, some feldspar grains display melted feldspar coatings. While multiple origins for these materials are possible – including an older crater and volcanism – the evidence best supports the 1908 Tunguska airburst hypothesis. The abundance of melted, shocked materials in the biomass-burning layer aligns with proposals that airburst fragments struck the Earth’s surface at velocities sufficient to produce shocked quartz. The coexistence of melted particles, shock-metamorphosed minerals, and unaltered grains suggests a heterogeneous energy distribution that created shallow craters and melted surface materials. These findings advance our understanding of airburst/impact mechanics, but few people have ever observed a dangerous airburst like Tunguska, so very little is known about them. Lacking sufficient real-world data, scientists should continue modeling these dangerous low-altitude airbursts to understand them better. The Tunguska event is a valuable case study demonstrating the urgent need to improve our planetary defense strategies.

Asteroid and comet impacts can produce a wide range of effects, varying from large crater-forming events to high-altitude, non-destructive airbursts. Numerous studies have used computer hydrocode to model airbursts, primarily focusing on high-altitude events with limited surface effects. Few have modeled so-called “touch-down” events when an airburst occurs at an altitude of less than ∼1000 m, and no known studies have simultaneously modeled changes in airburst pressures, temperatures, shockwave speeds, visible materials, and bulk material failure for such events. This study used the hydrocode software Autodyn-2D to investigate these interrelated variables. Four airburst scenarios are modeled: the Trinity nuclear airburst in New Mexico (1945), an 80-m asteroid, a 100-m comet, and a 140-m comet. Our investigation reveals that touch-down airbursts can demolish buildings and cause extensive ground-surface damage. The modeling also indicates that contrary to prevailing views, low-altitude touch-down airbursts can produce shock metamorphism when the airburst shockwave or fragments strike Earth’s surface at sufficiently high velocities, pressures, and temperatures. These conditions can also produce microspherules, meltglass, and shallow impact craters. Regardless of modeling uncertainties, it is known that bolides can burst just above the Earth’s surface, causing significant damage that is detectable in the geologic record. These results have important implications for using shocked quartz and melted materials to identify past touch-down airbursts in the absence of a typical impact crater. Although relatively rare, touch-down events are more common than large crater-forming events and are potentially more dangerous.

Sediment sequences spanning the 12,800-year-old lower Younger Dryas boundary (YDB) were investigated at three widely separated sites in eastern North America (Parsons Island, Maryland, a Newtonville sandpit in southern New Jersey, and Flamingo Bay, South Carolina). All sequences examined exhibit peak abundances in platinum (Pt), microspherules, and meltglass representing the YDB cosmic impact layer resulting from the airbursts/impacts of a fragmented comet ∼12,800 years ago. The evidence is consistent with the Younger Dryas impact hypothesis (YDIH) recorded at ∼50 other sites across North and South America, Europe, Asia, and the Greenland ice sheet. These sequences were also examined for shock-fractured quartz, based on a recent study suggesting that low-shock metamorphism may result from low-altitude bolide airbursts similar to that observed during near-surface atomic detonations. Now, for the first time in a suite of well-separated sites in North America, we report in the YDB the presence of quartz grains exhibiting shock fractures containing amorphous silica. We also find in the YDB high-temperature melted chromferide, zircon, quartz, titanomagnetite, ulvöspinel, magnetite, native iron, and PGEs with equilibrium melting points (∼1,250° to 3,053°C) that rule out anthropogenic origins for YDB microspherules. The collective evidence meets the criteria for classification as an “impact spherule datum.”

A previous study presented evidence supporting the hypothesis that a low-altitude airburst approximately 3600 years ago destroyed Tall el-Hammam, a Middle-Bronze-Age city northeast of the Dead Sea in modern-day Jordan. The evidence supporting this hypothesis includes a widespread charcoal-and-ash-rich terminal destruction layer containing shock-fractured quartz, shattered and melted pottery, melted mudbricks and building plaster, microspherules, charcoal and soot, and melted grains of platinum, iridium, nickel, zircon, chromite, and quartz. Here, we report further evidence supporting a cosmic airburst event at Tall el-Hammam. Fifteen years of excavations across the city revealed a consistent directionality among scattered potsherds from individually decorated vessels, including one potsherd group distributed laterally approximately southwest to northeast across ∼22 m, spanning six palace walls. Similar trails of charred grains, charcoal, and bone fragments were also found distributed across multi-meter distances inside the destroyed city. Although an earlier report of the directionality of this debris was challenged, further evidence presented here strengthens that interpretation. We also report Middle-Bronze-Age partially melted breccia that likely formed at >2230 °C, consistent with a cosmic event. We investigated additional glass-filled fractured quartz grains using ten analytical techniques, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), cathodoluminescence (CL), and electron backscatter diffraction (EBSD). These grains are inferred to have formed by high-pressure shock metamorphism, consistent with an earlier report that has been challenged. To test that the mode of destruction could have been an airburst, we produced a hydrocode computer model of a Type 2 or touch-down airburst, in which a high-temperature, high-pressure, high-velocity jet intersects Earth’s surface, producing meltglass, microspherules, and shock metamorphism. The modeling shows that the explosive energy released can propel high-velocity airburst fragments to strike the Earth’s surface, producing shock metamorphism and creating superficial craters potentially susceptible to geologically rapid erosion. Although the probability of such airbursts is low, the potential for substantial damage is high, especially in cities.

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.

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 Wakulla Springs. A YDB age of ~ 12.8 ka for the platinum and spherule chronostratigraphic datum in these Wakulla Springs sequences is consistent with the archaeological data and OSL dating. This study confirms the utility of this YDB datum layer for intersequence correlation and for assessing relative ages of Paleoamerican artifacts, including those of likely Clovis, pre-Clovis, and post-Clovis age and their possible responses to environmental changes known to have occurred during the Younger Dryas cool climatic episode.