Wendy S. Wolbach

Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling

A carbon-rich black layer, dating to ≈12.9 ka, has been previously identified at ≈50 Clovis-age sites across North America and appears contemporaneous with the abrupt onset of Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene megafauna, along with Clovis tool assemblages, occur below this black layer but not within or above it. Causes for the extinctions, YD cooling, and termination of Clovis culture have long been controversial. In this paper, we provide evidence for an extraterrestrial (ET) impact event at ≅12.9 ka, which we hypothesize caused abrupt environmental changes that contributed to YD cooling, major ecological reorganization, broad-scale extinctions, and rapid human behavioral shifts at the end of the Clovis Period. Clovis-age sites in North American are overlain by a thin, discrete layer with varying peak abundances of (i) magnetic grains with iridium, (ii) magnetic microspherules, (iii) charcoal, (iv) soot, (v) carbon spherules, (vi) glass-like carbon containing nanodiamonds, and (vii) fullerenes with ET helium, all of which are evidence for an ET impact and associated biomass burning at ≈12.9 ka. This layer also extends throughout at least 15 Carolina Bays, which are unique, elliptical depressions, oriented to the northwest across the Atlantic Coastal Plain. We propose that one or more large, low-density ET objects exploded over northern North America, partially destabilizing the Laurentide Ice Sheet and triggering YD cooling. The shock wave, thermal pulse, and event-related environmental effects (e.g., extensive biomass burning and food limitations) contributed to end-Pleistocene megafaunal extinctions and adaptive shifts among PaleoAmericans in North America.

Global fire at the Cretaceous– Tertiary boundary

Cretaceous-Tertiary (K-T) boundary clays from five sites in Europe and New Zealand are 102-104-fold enriched in elemental C (mainly soot), which is isotopically uniform and apparently comes from a single global fire. The soot layer coincides with the Ir layer, suggesting that the fire was triggered by meteorite impact and began before the ejecta had settled.

Fullerenes in the cretaceous-tertiary boundary layer

High-pressure liquid chromatography with ultraviolet-visible spectral analysis of toluene extracts of samples from two Cretaceous-Tertiary (K-T) boundary sites in New Zealand has revealed the presence of C60 at concentrations of 0.1 to 0.2 parts per million of the associated soot. This technique verified also that fullerenes are produced in similar amounts in the soots of common flames under ambient atmospheric conditions. Therefore, the C60 in the K-T boundary layer may have originated in the extensive wildfires that were associated with the cataclysmic impact event that terminated the Mezozoic era about 65 million years ago.

Elemental carbon in sediments: Determination and isotopic analysis in the presence of kerogen

A procedure has been developed for separate measurement and isotopic analysis of kerogen and elemental C (soot, charcoal) in sedimentary rocks. The carbonaceous residue left after HF-HCl dissolution is oxidized with 0.10 MCr2O7= in 2 MH2SO4 at 50°C. Kerogen reacts with a half-life of 6–180 hrs, depending on maturity, and thus can be quantitatively removed from elemental C, which reacts more slowly (t12 ≈ 600–2000 hr). The amount and isotopic composition of kerogen and elemental C are then obtained by measurement of etched and unetched samples, after applying a correction for the loss of elemental C in the etch. The rate of the oxidation reaction has been studied in detail for carbon black and for carbonaceous residues from 2 K-T boundary clays, and less extensively for 12 samples of charcoal and kerogen. Most materials obey first-order kinetics to a fair approximation, but carbon black and K-T soot—both consisting of spherules—show a sudden, 4.0 or 1.7-fold increase in the rate after a mass loss of 23 or 82%, respectively. Apparently the interiors of soot spherules are more reactive than the exteriors.

Nanodiamonds in the Younger Dryas Boundary Sediment Layer

We report abundant nanodiamonds in sediments dating to 12.9 ± 0.1 thousand calendar years before the present at multiple locations across North America. Selected area electron diffraction patterns reveal two diamond allotropes in this boundary layer but not above or below that interval. Cubic diamonds form under high temperature-pressure regimes, and n-diamonds also require extraordinary conditions, well outside the range of Earths typical surficial processes but common to cosmic impacts. N-diamond concentrations range from ≈10 to 3700 parts per billion by weight, comparable to amounts found in known impact layers. These diamonds provide strong evidence for Earths collision with a rare swarm of carbonaceous chondrites or comets at the onset of the Younger Dryas cool interval, producing multiple airbursts and possible surface impacts, with severe repercussions for plants, animals, and humans in North America.

Shock-synthesized hexagonal diamonds in Younger Dryas boundary sediments

The long-standing controversy regarding the late Pleistocene megafaunal extinctions in North America has been invigorated by a hypothesis implicating a cosmic impact at the Ållerød-Younger Dryas boundary or YDB (≈12,900 ± 100 cal BP or 10,900 ± 100 14C years). Abrupt ecosystem disruption caused by this event may have triggered the megafaunal extinctions, along with reductions in other animal populations, including humans. The hypothesis remains controversial due to absence of shocked minerals, tektites, and impact craters. Here, we report the presence of shock-synthesized hexagonal nanodiamonds (lonsdaleite) in YDB sediments dating to ≈12,950 ± 50 cal BP at Arlington Canyon, Santa Rosa Island, California. Lonsdaleite is known on Earth only in meteorites and impact craters, and its presence strongly supports a cosmic impact event, further strengthened by its co-occurrence with other nanometer-sized diamond polymorphs (n-diamonds and cubics). These shock-synthesized diamonds are also associated with proxies indicating major biomass burning (charcoal, carbon spherules, and soot). This biomass burning at the Younger Dryas (YD) onset is regional in extent, based on evidence from adjacent Santa Barbara Basin and coeval with broader continent-wide biomass burning. Biomass burning also coincides with abrupt sediment mass wasting and ecological disruption and the last known occurrence of pygmy mammoths (Mammuthus exilis) on the Channel Islands, correlating with broader animal extinctions throughout North America. The only previously known co-occurrence of nanodiamonds, soot, and extinction is the Cretaceous-Tertiary (K/T) impact layer. These data are consistent with abrupt ecosystem change and megafaunal extinction possibly triggered by a cosmic impact over North America at ≈12,900 ± 100 cal BP.

Evidence from central Mexico supporting the Younger Dryas extraterrestrial impact hypothesis

We report the discovery in Lake Cuitzeo in central Mexico of a black, carbon-rich, lacustrine layer, containing nanodiamonds, microspherules, and other unusual materials that date to the early Younger Dryas and are interpreted to result from an extraterrestrial impact. These proxies were found in a 27-m-long core as part of an interdisciplinary effort to extract a paleoclimate record back through the previous interglacial. Our attention focused early on an anomalous, 10-cm-thick, carbon-rich layer at a depth of 2.8 m that dates to 12.9 ka and coincides with a suite of anomalous coeval environmental and biotic changes independently recognized in other regional lake sequences. Collectively, these changes have produced the most distinctive boundary layer in the late Quaternary record. This layer contains a diverse, abundant assemblage of impact-related markers, including nanodiamonds, carbon spherules, and magnetic spherules with rapid melting/quenching textures, all reaching synchronous peaks immediately beneath a layer containing the largest peak of charcoal in the core. Analyses by multiple methods demonstrate the presence of three allotropes of nanodiamond: n-diamond, i-carbon, and hexagonal nanodiamond (lonsdaleite), in order of estimated relative abundance. This nanodiamond-rich layer is consistent with the Younger Dryas boundary layer found at numerous sites across North America, Greenland, and Western Europe. We have examined multiple hypotheses to account for these observations and find the evidence cannot be explained by any known terrestrial mechanism. It is, however, consistent with the Younger Dryas boundary impact hypothesis postulating a major extraterrestrial impact involving multiple airburst(s) and and/or ground impact(s) at 12.9 ka.

Geochemical Markers of the Cretaceous-Tertiary Boundary Event at Brazos River, Texas, USA

The Cretaceous-Tertiary boundary sites around the Gulf of Mexico are close to the Chixculub impact site and are relatively well studied, yet much remains to be learned about them. Therefore, the first integrated study of carbon, soot, and fullerenes in a Cretaceous-Tertiary boundary section was undertaken at the Brazos-1 site on the Brazos River in Texas at the most complete section of end Cretaceous and basal Paleocene deposits on the Texas segment of the Gulf Coast area. Up to 409 ppm of native sulfur (So) were serendipitously discovered in a spherule-bearing unit of the BR-1 section, and lesser amounts were found in spherule-bearing units of nearby Brazos riverbed sections in a section on Darting Minnow Creek. The isotopic composition, δ33S = −12.97‰, δ34S = −24.89‰, and δ36S = −46.4‰, implies that this So cannot have come to Earth by the impactor that formed the Chicxulub crater, but, most likely, was produced by sulfate-reducing bacteria during a local, transient bacterial bloom for which the sulfate was provided by CaSO4-bearing spherules. Carbon and soot were determined in twelve samples representing all units of BR-1 from the Cretaceous Corsicana/Kemp Formation to the Tertiary Kincaid Formation. A significant increase of C and soot contents, up to 2.2×104 ppm and 1.4×104 ppm, respectively, occurs in a sandy bed at the top of the KT complex. Fullerenes were determined in fifty-four samples from all units of the same BR-1 section. Less than 1 ppb was reliably detected at the same sandy bed where the strongest Ir anomaly of the section is known to occur. It is suggested here that the Chicxulub impact 65 Ma ago ignited local wildfires that produced C, soot, and fullerene, which settled onshore, or near-shore, whence they were transported to the Brazos site by coastal flooding and associated sediment-laden water plumes moving offshore.

Fires at the K/T boundary: Carbon at the Sumbar, Turkmenia, site

Abstract We have measured carbon at the marine K/T boundary site SM-4 at the Sumbar river in Turkmenia, USSR, which has an undisturbed Ir profile and the largest known Ir anomaly (580 ng/cm 2 ). Twenty samples, ranging from −100 to +100 cm, were analyzed to determine the concentration and δ 13 C of elemental carbon and kerogen, using a Cr 2 O 7 oxidation method (Wolbach and Anders, 1989) to resolve these components. The samples were unusually complex, containing 3 kerogen components of distinctive IR spectra and half-lives in Cr 2 O 7 (~200, ~100, and ⪡60 h), in addition to soot and charcoal from the K/T fire. The elemental C has δ 13 C = −25.96 ± 0.6 l%o, close to the mean for 11 K/T sites (-25.8 ± 0.6%; 11 mg/cm 2 ). The first of the 2 kerogen components (δ 13 C = −22.8%), which dominates in the Cretaceous, appears to come from detrital carbonaceous shale; the second (δ 13 C = −27.7%o) occurs only in the boundary clay and may come from land plant material swept to sea, or phytoplankton grown in the presence of excess, light CO 2 from fires on land. The great thickness of the boundary clay (10.5 cm) permits determination of the compositional profiles with unprecedented spatial resolution. Ir and shocked quartz—both representing impact ejecta—rise sharply at the boundary, peak in the basal layer, and then decline. Soot and total elemental C show a similar spike in the basal layer but then rise rather than fall, peaking at 7 cm. Apparently fires started before the basal layer had settled, implying that ignition and spreading of major fires became possible if not immediately then very soon after the impact. There is no basis for claims by Hansen et al. (1987) that K/T carbon black first occurs 3.5 m below the Danish K/T boundary and has δ 13 C of −27.4 to −27.8%o. Reexamination of a sample from Nye Klov shows that these authors confused kerogen with carbon black.

Hydrogen bonding by alcohols and amines

The pure base calorimetric method has been used to determine the enthalpies of hydrogen bond complex formation between aliphatic amines and alcohols. The enthalpies of complexation for the series methanol-n-butanol bonding with triethylamine increase with decreasing alkyl chain length in accordance with the electron donating properties of alkyl groups. Unexpectedly, the enthalpies for the complexes of n-butanol with tributylamine, tripropylamine, and triethylamine increase with decreasing alkyl chain length.Primary and secondary amines form hydrogen bonded complexes with n-butanol in which the amine protons form an NH···O bond with the alcohol and the alcohol hydroxyl proton donates a proton to the amine nitrogen. The difference in enthalpy of complex formation between tertiary amines and secondary amines is largely accounted for by the involvement of the amine proton of the secondary amine. Primary amines, like secondary amines, donate only one proton to the complex with n-butanol but have a larger complex enthalpy than secondary amines probably because of steric hindrance and differences in basicity.