Evidence for an Extraterrestrial Impact Event 12,900 years ago that Contributed to Megafaunal Extinctions and the Younger Dryas Cooling
The Younger Dryas event boundary (YDB) is a thin sedimentary layer of 12.9 ka age containing an assemblage of materials formed due to a major ET impact centered over northern North America. The event coincided with the megafaunal extinctions and the Younger Dryas cooling episode. The YDB layer contains peaks in magnetic grains, microspherules, and iridium, in addition to charcoal and soot that resulted from extensive wildfires. Two impact-related carbon-rich markers, glass-like carbon and carbon spherules, have not been reported previously in North America. Vesicular, glass-like carbon, in pieces up to several cm, occurs in the YDB at 22 sites with concentrations ranging up to 16 g/kg. Their glassy texture suggests melting during formation, with some fragments grading into charcoal, and CF-IRMS analysis reveals a composition of >70 percent carbon. One sample exhibited a strong fullerene signature containing ET helium with a ratio of 84× that of air, comparable to the Tagish Lake meteorite (90×). Similar glass-like carbon has been reported from the Azuara crater in Spain (Ernstson, et al. 2001). Carbon spherules (0.15-2.5 mm) are black, highly vesicular, low-density, subspherical-to-spherical objects found in 18 widely distributed sites at varying concentrations up to 1500/kg. SEM analysis shows that the spherules have cracked and patterned surfaces, honeycombed cells, no inclusions, and sometimes display hollow cores. SEM/EDS and microprobe analyses show the carbon spherules to be >75 percent carbon. Similar carbon spherules are reported from the a crater in Germany (Rösler, et al., 2005). The carbon spherules most likely are either ablation products from the impactor or combustion products of the impact. Sediment samples were analyzed for Ir, and YDB samples from 9 sites exhibited elevated Ir values up to 3.75 ppb, while there was no detectable Ir above or below the YDB. Extracted magnetic grains have values up to 117 ppb, which is 25 percent that of typical chondrites and up to 5000× crustal abundance. The YDB layer, representing a major ET impact event at 12.9 ka, appears to coincide with the late Pleistocene megafaunal extinction and the onset of Younger Dryas cooling. We propose that neither this cooling nor the extinction would have occurred in the absence of this impact event.
Correlation of the Late Pleistocene Usselo Horizon (Europe) and the Clovis Layer (North America)
In 1940, a dark charcoal-rich layer, 10 to 15cm thick, was found within the Late Pleistocene Coversands of the Netherlands, and named the Usselo Layer (de Laag van Usselo) by its discoverer, archaeologist CCJW Hijszeler (1902-1982). Usselo is a village near Enschedé, a few kilometres from the Dutch-German border. Research started after the war, and publications, both scientific and popular, came forth in the 1950s. By pollen content, the layer was dated to the Alleröd, the last interstadial of the Würm (Wisconsin) glaciation; radiocarbon dating indicated (pre-AMS) dates of about 11,200 14C BP. Identification of the layer at other localities was visual, and it was found in Belgium, France, Germany, Poland, and Belarus; it was also found in the UK and in Denmark, in which countries, however, no correlation was made with the other occurrences. Hijszeler had found the layer all over the Netherlands and abroad from Ostende to Hamburg, and he hypothesized the cause as a general wildfire provoked by the eruption of an Eiffel volcano. The European geologists and archaeologists, however, did not adopt his views and interpreted the layer as a paleosol, vitiating the chronology by representing the layer as the result of a long development, instead of as an eolian sediment laid down perhaps in a day or even less that provides us with a sharp marker horizon. The prehistoric Clovis culture of North America was found in the 1930s and dated to the Twocreekan, the last interstadial of the Wisconsin glaciation. The Clovis layer was especially investigated by archaeologist C.Vance Haynes Jr. Visually, the layer is easily identifiable with the Usselo Horizon of Europe. Its stratigraphic position is coincident with the end of the Clovis culture and with the disappearance of the Pleistocene megafauna. In Europe, there is a clear correlation with the sudden demise of the Magdalenian culture, best known for the Franco-Cantabrian cave paintings, and with megafaunal extinctions such as those of the Irish elk, the cave bear, and cave lion. Recently, Richard Firestone and Allen West in North America have carried out an intensive field and laboratory investigation, suspecting an extraterrestrial cause for the extinctions and the cultural discontinuity, with the Clovis layer as the extinction layer, an all-important witness to the catastrophe. They achieved positive results, the most spectacular one perhaps being the iridium content, because that element became well-known in the 1980s as an impact indicator in the K-T boundary layer. Other results include the presence of glass-like carbon, magnetic microspherules, and high levels of potassium-40. Being aware of the similarities in the Late Pleistocene stratigraphical records of Europe and North America, I contacted Firestone and West in 2005, and early in 2006 I sent them samples of the Usselo Horizon from Lommel, Belgium. The analyses they carried out yielded high levels of impact indicators, including magnetic grains, metallic spherules, carbon glass, charcoal, and in the magnetic fraction, high iridium content. These findings largely confirm the identity of the two ET impact layers on either side of the Atlantic Ocean. Hijszeler(1957) Geol.Mijnb.NS 19: 288-302. Haynes and Hemmings (1968) Science 159: 186-7. Wolbach, et al. (1985) Science 230: 167-170. Kloosterman (1999) Symp. New Scenarios of Solar System Evolution, Univ.Bergamo. (Abstract 2002). Kloosterman (2000) De Laag van Usselo, de Wereldbrand en de Verdwijntruc. Bres 201: 63-74. Kloosterman (2006) "De Komeetinslag van 13.000 jaar geleden." Frontier Mag. 12/1: 44- 45. Firestone, et al. (2006) The Cycle of Cosmic Catastrophes. Bear and Co., Rochester, Vermont.
Is There Evidence for Impact-Triggered Fires at the End Pleistocene?
Recent evidence suggests an extraterrestrial contribution to the End Pleistocene extinctions. Sediments at the base of a carbon-rich, dark layer dating to ~12.9 ka contain magnetic grains, microspherules, elevated Ir, fullerenes with abundant 3He, and other evidence consistent with extraterrestrial impact . To test the possibility that combustion of the impactor, carbon-bearing rocks, or biomass could have been triggered by the impact (as hypothesized at the End Cretaceous 65 Ma ago ), we searched for soot in a variety of Clovis-age sites marked by this dark layer in North America, Germany, and Belgium. Thirty-eight samples from the following North American sites were studied: Carolina Bays at Blackville and Myrtle Beach, SC; Murray Springs, AZ; Chobot Site, Alberta, Canada; Blackwater Draw, Clovis, NM; Glacial Lake Hind, Manitoba, Canada; Daisy Cave, San Miguel Channel Island, Santa Barbara. Four samples from the Usselo Horizon in Schleswig-Holstein and one sample from Lommel, Belgium were also analyzed. Dissolution and analysis procedures were based on those used successfully for detecting soot from impact- produced wildfires at the Cretaceous-Tertiary (K/T) boundary [3, 4, 5]. Reduced carbon was isolated from sediments using HCl and HCl/HF. Elemental carbon was separated from organic carbon by acidic dichromate oxidation. Any remaining minerals were removed from carbonaceous residues using sodium metatungstate density separation. The elemental carbon of interest (soot) was identified and characterized using SEM imaging and quantified by weighing and particle size analysis. Two of the samples contained significant quantities of soot: Murray Springs, AZ, with a soot content of 21 ± 5 ppm; and Carolina Bay, Blackville, SC, with a soot content of 1969 ± 167 ppm. None of the remaining End Pleistocene samples studied showed significant soot contents. Negative results do establish that surface contamination by soot was not a problem, even though some sample locations were undoubtedly close to automobile traffic or possible natural biomass fires. The magnitude and location of the End Pleistocene bolide is unknown and so it is impossible to predict the magnitude of any fires triggered by the impact. The presence of significant soot, however, especially the large amount at the Carolina Bay, suggests that significant burning at the very least occurred near that location ~12.9 ka ago. The fire that produced the observed soot might have been regional, or perhaps soot was initially deposited at additional sites but simply not preserved. These questions will be addressed by analyzing more End Pleistocene samples.  Firestone R.B., West A., Kennett J.P., Becker L., Bunch T.E., et al., Proceedings of the National Academy of Sciences, submitted.  Wolbach W. S., Lewis R. S., and Anders E. (1985) Science 230, 167-170.  Wolbach W.S., Gilmour I., Anders E., Orth C.J., and Brooks R.R. (1988) Nature 334, 665-669.  Wolbach W.S. and Anders E. (1989) Geochimica et Cosmochimica Acta 53, 1637-1647.  Wolbach W.S., Gilmour I., and Anders E. (1990) In: Global Catastrophes in Earth History (eds. V.L. Sharpton and P. Ward). Geological Society of America Special Paper 247, 391-400.
Did a Bolide Impact Trigger the Younger Dryas and Wipe Out American Megafauna? A Skeptic's Reaction to an Intriguing Hypothesis.
Perhaps there is credible physical evidence of a bolide impact in North America at 12,900 cal BP. However, several incongruous aspects of the paleoclimatic, archaeological, and faunal records of the Terminal Pleistocene must be addressed to allay skepticism about the hypothesis of dramatic effects upon humans or megafauna: 1) Paleoindian populations (e.g., Folsom, Dalton) thrived after the Younger Dryas (YD) onset; 2) megafauna, including giant sloths were wiped out in Florida, but medium-sized sloths in the Caribbean islands (including Cuba) survived into the mid-Holocene; 3) South American megafauna survived until at least 12,500 cal BP, probably longer; why was there not a synchronous extinction? 4) Late Pleistocene cold reversals in Antarctica and southern South America are not synchronous with the YD; 5) Bison and grizzly survived, and elk and moose expanded into North America in the Terminal Pleistocene-Early Holocene; why did they survive and thrive? 6) Mammoths survived on Wrangel Island and probably in pockets in Siberia well into the Holocene; why did the supposed impact in the Arctic not wipe them out? 7) Finally, the YD ended at 11,590 cal BP even more abruptly than it began (over less than a decade); does this require another impact? If not, why does the YD onset call for an extraterrestrial trigger?
How Many Mammoths Died at the End of the Pleistocene?
The extinction risks of Clovis-era mammoths and mastodons in North America may be roughly estimated in two ways: One method of estimating total numbers relies on the average density of related modern analogues, such as living elephants, and is based on the maximum extent of occurrence (the "range") of each extinct taxon examined. A second method of estimating populations roughly converts fossil record counts to population size based on documented "live-to-dead" ratios derived from actualistic studies of related modern taxa. The total number of megamammals alive just before extinction was probably surprisingly low.
The Younger Dryas ET Impact Theory and Terminal Pleistocene Mammalian Extinctions in North America
Despite decades of intensive study and debate, no consensus has been reached on what caused the extinction of North America's mammalian megafauna at the end of the Pleistocene. In a scholarly standoff, prominent scientists have shown that neither "human overkill" or "climate change" models adequately account for the patterns found in the paleontological and archaeological records of North America. The Younger Dryas ET Impact theory may dramatically alter this debate, adding a catastrophic trigger to help explain the rapid extinction of many large mammals about 12,900 years ago. New data suggest that an extraterrestrial impact focused in northern and eastern North America may have devastated the megafauna through: (1) direct mortality caused by the impacts shock wave, debris, and massive wildfires; (2) dramatic reduction of terrestrial food supplies, rapid climatic change, and ecological reorganization; and (3) coup-de-grace effects of surviving human populations rapidly expanding after the impact.
The Pleistocene-Holocene Unconformity in California Prehistory
The earliest archaeological record from California shows a dramatic unconformity or cultural hiatus between the terminal Pleistocene and the early Holocene. Clovis-like fluted projectile points which mark initial human colonization ca. 13,300-12,900 cal BP, are relatively common and have been found throughout the state, but almost exclusively as isolates. Early Holocene sites are abundant as well, particularly on the coast where at least 23 deposits show occupation as old as ca. 10,000-9000-cal BP. Only one of these, Daisy Cave, extends back into the terminal Pleistocene, but the remainder mark occupations that began only at the onset of the Holocene. There are almost no archaeological sites in California that date between 12,900 and 10,300 cal BP or that exhibit superimposed terminal Pleistocene and early Holocene components. This pattern is consistent with a significant disruptive event during the Younger-Dryas.
Changes in Paleoindian Projectile Point Densities as Possible Evidence of a Clovis Demographic Collapse in the Southeastern U.S.
Recent evaluation by the author of the South Carolina Paleoindian point database indicates the substantial presence of a suspected Middle Paleoindian point historically known as Redstone (Cambron and Hulse, 1964; Mason, 1962; Perino, 1968; Williams and Stoltman, 1965). Because of recent discoveries in South Carolina of large fluted points typical of the Redstone, it became clear that the Redstone had a straight to trianguloid blade configuration from the earliest stage of its use life. Lanceolates with extremely long prominent flutes heretofore had been classified as Clovis (Charles and Michie, 1992; Goodyear et al., 1990; Michie, 1977). Accordingly, a review of all fluted points yielded a total of 48 Redstones that had previously been misclassified as Clovis. Reclassifying the South Carolina database resulted in approximately four Clovis points for every one Redstone. Using Clovis and Redstone fluted points made from coastal plain Allendale-type chert and high-quality metavolcanics, a total of 179 Clovis were found versus 40 Redstones (4.5 to 1). Within the Allendale chert cases, 115 were Clovis versus 24 Redstone (4.8 to 1). Within metavolcanics, it was 64 Clovis versus 16 Redstones (4 to 1). Assuming Redstones date from 10,800 to 10,500 RCYBP, and Clovis dates from 11,300 to 10,900 RCYBP, a precipitous decline in post-Clovis fluted points is indicated. No other Paleoindian points are known for this area of the Southeast to fill in this time period, since Daltons presumably began later around 10,500 RCYBP (Goodyear 1982). For the Allendale County region of South Carolina, there are an estimated 20 Dalton points for every Redstone. This apparent decline in Redstone projectile points occurs during the Younger Dryas, a time thought to be colder and dryer than Clovis times, and therefore, less hospitable. The strong presence of Dalton points throughout the Southeast would suggest any demographic problems were ameliorating by Dalton times. As a cross-check on the South Carolina database, the North Carolina Paleoindian point survey was also reclassified searching for Redstones. It resulted in a Clovis to Redstone ratio of 3 to 1 (Daniel and Goodyear, 2006). This pattern of a high Clovis to Redstone ratio apparently is not restricted to the Carolinas. In his survey of the Nottaway River drainage in southeast Virginia, McAvoy (1992) found a dramatic post-Clovis drop in what he calls deep concave based fluted points and sites. He postulates a major population reduction in this region after Clovis times. For the entire Virginia data base, Johnson (1996) notes that the proportion of concave base to presumably Clovis points is 11 percent. Based on these results, more attention should be paid to a possible post-Clovis, pre-Dalton decline in Paleoindian points in the Southeast, and perhaps elsewhere, to determine the archaeological reality of this suggested pattern.
Mammoths and Humans as Late Pleistocene Contemporaries on Santa Rosa Island, Channel Islands National Park, California.
AMS radiocarbon dating of a pygmy mammoth (Mammuthus exilis) thoracic vertebra and associated charcoal has provided evidence for the contemporaneity of the pygmy mammoth and early human remains on Santa Rosa Island, Channel Islands National Park, California. Charcoal associated with the vertebra dated 11,010 ±70 RC yr B.P. (B-133594). That date was significantly close to the extinction date for continental mammoths to warrant a date directly on the bone. The vertebral centrum was drilled and submitted for bone collagen dating by Stafford. The resultant date was 11,030 ±50 RC yr. B P (CAMS-71697), only 20 14C years older than the charcoal date. The significance of the dates was immediately apparent, because a date from human remains from the Arlington Springs Site (CA-SRI-173), Santa Rosa Island was 10,960 ±80 RC yr B.P. (CAMS-16810) (Johnson et al., 1999) - a date nearly identical with the M. exilis measurement. The contemporaneity of the mammoth bone date and human bone date indicates that mammoths were still extant on the islands when humans arrived. These data are from only one mammoth and one human ... more research needs to be done on the mammoth and human remains on the island. Was the contemporaneity coincidence, or the prelude to extinction?
Formation of the Carolina Bays: ET Impact vs. Wind-and-Water
The Carolina Bays are a group of lakes, wetlands, and depressions, stretching from Florida to New Jersey along the Atlantic Ocean, and ranging up to 11 km in length and about 15 m in depth. Their distinctive elliptical shapes and common orientation towards the Great Lakes region have generated many hypotheses about their method of formation, including extraterrestrial impact (Melton and Schriever, 1933; Prouty, 1934). Another suggests that springs or groundwater dissolution of soluble minerals caused subsidence, which formed water-filled depressions that became the Bays (Johnson, D.W., 1944). One of the prevailing views is that Carolina Bays represent irregular lakes that were gradually reshaped into ellipses by circulating lake currents, generated by strong ice-age winds blowing perpendicular to the current long axes of the Bays (Kaczorowski, 1977). We report results from a suite of cores taken from within a Bay, which we have named "Howard Bay," located about 2 km north of the town of Duart in Bladen County, North Carolina. Located on the high western bluff of the Cape Fear River, the Bay is 2.7 km long, 1.6 km wide, and filled with about 9 meters of sediment with an encircling rim that is ~1-meter high. Analyses of seven cores along the long axis of Howard Bay reveal an assemblage of abundant magnetic grains, microspherules, carbon spherules, glass-like carbon, and iridium, typical of the YDB impact layer (12.9 ka) at many other sites across North America. The impact layer conforms to the basal contours of the basin, suggesting that the markers were deposited immediately or soon after the Bay formed. Further analyses of samples in complete core sequences reveal that, unlike typical, peat-rich Carolina Bays, Howard Bay essentially lacks peat, diatoms, pollen, or other organic materials, suggesting that this Bay never stored water for any sustained length of time. Furthermore, several trenches confirm that the deepest part of the Bay is filled with >6 m of cross-bedded eolian sand with no evidence of lacustrine sedimentation. This evidence calls into question prevailing hypotheses (a) that all Bays were lakes and ponds in the past and that their shapes were formed by wave action, or (b) that groundwater movement led to subsidence that formed the Bay. The presence of impact markers, including high concentrations of iridium, in a layer just above the basal sediments of this Bay that is filled with eolian sand supports the extraterrestrial impact hypothesis for Bay formation.