October 12, 2007, updated June 2008
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1. Geochemical Evidence Indicating an ET Cause to the Megafaunal Extinction.
The Cosmochemical Evidence of the YDB Group. At the May 2007 American Geophysical Union meeting in Acapulco, a group of researchers, the so-called "Younger Dryas Boundary (YDB) group," reported interesting findings pointing overwhelmingly to an extraterrestrial cause for the extinction of the Pleistocene megafauna. Particularly significant was the report of high concentrations of iridium (Ir) and other extraterrestrial material indicators at the Allerod/Younger Dryas boundary marking the terminal horizon in the extinction of the Pleistocene megafauna which dates around 12,950 calendar years before year 2000 (b2k) on the basis of the Cariaco Basin gray scale climate profile chronology. Since iridium is over 10,000 times more abundant in cosmic dust and chondritic meteorites than it is in terrestrial crustal material, it serves as an excellent ET material indicator. Other ET markers included magnetic grains, microspherules, and fullerenes saturated with the rare isotope helium-3. Their findings, many of which are reported in the group's PNAS paper (Firestone, et al., 2007), include the following:
Firestone, et al. (2007a, 2007b) report detecting 3.75 ppb of Ir in sediment samples taken from the Allerod/Younger Dryas (AL/YD) boundary at nine Clovis-age sites, with no Ir being detectable above or below this horizon. Magnetic grain microspherules extracted from this boundary were found to contain up to 51 ppb of Ir at North American sites as well as considerable amounts of the cosmic indicators nickel and cobalt. Grains from a site in Belgium were found to contain 117 ppb Ir, equivalent to 25% of the value typical of chondrites.
Wolbach, et al. (2007) report that sediments at the base of a 12,900 calendar years B.P. carbon-rich dark layer coincident with the AL/YD boundary and containing significant amounts of soot contained high concentrations of Ir, magnetic grains, microspherules, and fullerenes abundant in 3He.
Kobres, et al. (2007) report analysis of seven cores penetrated along the long axis of Howard Bay in North Carolina, which is one of the many elliptical depressions known as the "Carolina Bays." They find elevated Ir concentrations, abundant magnetic grains, microspherules, and carbon spherules similar to assemblages found in the YD boundary layer and conclude that these were deposited either immediately before or soon after the bay was formed.
West, et al. (2007) report detecting some of the highest AL/YD boundary ET markers in sediments from the Gainey Clovis site in Michigan, which included iridium, magnetic grains, microspherules, carbon spherules, soot, and fullerenes with ET helium. At the Topper Clovis site in South Carolina, they also report finding AL/YD boundary ET markers in a 5 cm thick layer lying immediately above the Clovis artifacts. Also they report finding iridium at 51 ppb (10% chondritic concentrations) inside an extinct horse skull at the Wally's Beach Clovis kill site suggestive of rapid burial following the YD event. They also examined several other sites that date to 12.95 kyrs b2k: glacial Lake Hind in Manitoba, Canada, an ice-aged drumlin at Morley in Alberta, Canada, Daisy Cave on the Channel Islands of California, and Lommel in Belgium. They report that the AL/YD boundary layer, which was evident at all of these sites, contained abundant ET markers.
Darrah, et al. (2007) report that the Blackwater Draw Clovis site in New Mexico contains metallic iron grains while the Topper site in South Carolina also contains iron spherules, Fe-Ni metallic grains, and Fe-Ni oxides. They also analyzed fullerines taken from the AL/YD boundary and found that they contained helium with an extraterrestrial isotopic signature. Carbonaceous residues extracted from AL/YD boundary bulk sediments taken from two of the sites contained elevated concentrations of helium-3 (0.3 to 3.5 ncc/g 3He) with an ET isotopic 3He/4He ratio of 30 to 220, suggesting substantial exposure to galactic cosmic rays. In particular they report that the residue from Daisy Cave, California contains helium with an isotopic 3He/4He ratio of 374 to 800, indicative of a significant galactic cosmic ray input. They conclude that the increase in 3He concentrations (5 to 8 ncc/g) with ET 3He/4 isotopic ratios ranging from 10 to 25 near the AL/YD boundary likely reflects an increase in the flux of interstellar dust particles.
Preliminary evidence of ET indicators in Paleo-Indian artifacts dating to the time of the AL/YD boundary event were also reported in 1998 and 1999 internet postings. For example, in February 1999 William Topping called attention to the presence of 1) spherules/chondrules present on some of the particles embedded in Paleo-Indian artifacts, 2) a "spike" of magnetite/ilmenite particles and spherules in the sediments directly "on" the Paleo-Indian horizon at the Gainey site in Michigan, and 3) elevated chromium and nickel in sediments from the Gainey Paleo-Indian horizon as evidenced through XRF analysis. Also in a June 1998 internet posting Baker, Taylor, and Topping reported the existence of surface pits in cherts on Paleo-Indian artifacts some containing embedded particles, some as large as 100 microns, having spherule-like protrusions suggesting in-flight particle heating. They conclude that the embedded particles are of extraterrestrial origin and had been heated during hypervelocity flight through the atmosphere. Based on shotgun experiments he conducted, Topping estimates that the particles entered these cherts at speeds as high as 0.4 km/s.
The evidence unveiled by the YDB group clearly establishes beyond a doubt that the megafaunal extinction had an extraterrestrial cause. But whether it was due solely to one or more comet explosions or impacts is questionable. Firestone, West, and Smith (2006) also have done an admirable job in their book of making the case that the Earth was subject to intense bombardment by cometary masses of various sizes at the beginning of the Allerod/Younger Dryas transition. Their discussion of comet explosions taking place over eastern Canada and Michigan, and craters in the Carolinas and elsewhere appears convincing.
However, as the reader may discover below, their suggestion that the megafaunal demise was due exclusively to a comet impact or aerial comet explosion appears to be highly unlikely as does their contention that these comets were debris shot out from a recent supernova explosion. Their theory has captured the imaginations of many scientists and has served as the organizing nucleus for an impressive series of discoveries. But like all theories we must subject them to critical assessment and if necessary abandon them should they prove to be inadequate.