In PNAS in May 2013, a companion article to Bunch et al. appeared: “Evidence for deposition of 10 million tonnes of impact spherules across four continents 12,800 y ago.” Wittke et al. investigated in greater depth the same 18 sites as Bunch et al., finding microspherule peaks at each using SEM and X-ray spectrometry. They too considered the various possible origins of the microspherules, ruling out all but an extraterrestrial impact.
IRREPRODUCIBILITY
As these studies plainly show, the microspherule evidence reported by FEA has been reproduced by more than two dozen authors at nearly as many YDB sites. It is eminently reproducible.
The allegation of irreproducibility rests mainly on SEA but also on three other articles. All other claims derive from these four. Let us examine them in chronological order and ask why the authors did not find the microspherule evidence that so many others did find.
1. As we saw, SEA failed to use SEM and XRS and therefore could not have distinguished ET microspherules from terrestrial ones.
2. Another group found abundant microspherules in the YDB layer at Murray Springs but noted that they were also present on nearby rooftops, and assumed the two were the same: both deriving from human activities. They did not use SEM so could not distinguish the manmade rooftop spherules from those found at the YDB.
3. One group confirmed the finding of YDB microspherules at Murray Springs, AZ, but also reported that they were abundant at non-YDB sites in Chile. This “suggest[ed] that elevated concentrations of these markers arise from processes common to wetland systems, and not a catastrophic extraterrestrial impact event.” But since they performed no SEM or XRS analyses, their Chilean microspherules may well be terrestrial, which is likely since the Chilean sites are known to contain abundant volcanic spherules.
4. The Requiem authors report on their study of the YDB on the Santa Barbara Channel Islands, saying that their four sample locations were “identical or nearly identical” to those reported by Kennett et al., who as we saw found microspherule and nanodiamond peaks. However, the location coordinates published by the Requiem authors differ from those of Kennett et al. by up to 7,000 m (4.3 mi), and none were at the exact same locations. It is clear that in spite of what they wrote, the Requiem authors did not sample where Kennett et al. sampled. But perhaps they sampled the YDB at some other location.
The Requiem authors say that “No clear YDB ‘marker bed’ was present in any of our sections, so our results focus on spherules through sediments pre-dating, dating to, and post-dating the onset of the YD.” This is tantamount to saying that they did not locate the YDB and thus could have sampled it only by chance. If one cannot locate the YDB and so must sample around it, almost by definition any microspherules found are unlikely to be extraterrestrial and any existing peaks are almost sure to be missed.
As confirmation, the Requiem paper includes two cross-sections from Channel Island sites that show the levels from which their samples came. A close inspection of their stratigraphic section for Santa Cruz Island confirms that they sampled above and below the YDB, but not at it nor even close to it. Their accompanying figure for Santa Rosa Island, site of the Arlington Canyon section sampled by Kennett et al., shows that they likely did not sample the YDB there either. These same samples from the Channel Islands, which did not come from the YDB, were later used to refute the evidence of nanodiamonds at the YDB. We will come back to this argument in the next chapter.
Thus none of the four studies actually demonstrate that the microspherule finding is irreproducible. In contrast, the studies by LeCompte et al., Bunch et al., and Wittke et al. did find abundant microspherules. Other researchers have found them at sites on four continents
To sum up: at more than two dozen YDB sites, researchers who clearly sampled the YDB layer and who used SEM and XRS have never failed to reproduce the distinctive ET microspherule peaks. Clearly, something went wrong with SEA’s analysis. What, we do not know and probably never will. But something did and all the articles that cited it as evidence that the YDIH was irreproducible were based on a false foundation.
9
PRECIOUS STONES
The platinum group elements (PGEs) comprise six “precious” metals clustered side-by-side in the periodic table: ruthenium, rhodium, palladium, osmium, iridium, and platinum. They are much more common in meteorites than in earthly rocks, so that when we find them elevated, we suspect an ET event.
As we noted, as meteorites pass through the atmosphere, their outer surfaces ablate and the resulting particles sift down to the surface. The Alvarezes thought the regularity of the process might allow the amount of iridium to serve as a geologic clock, but instead found it anomalously elevated, the clue that led to their discovery of the cause of dinosaur extinction.
After the Alvarez finding, elevated iridium became a key criterion of meteorite impact. To quote from the Requiem, “The platinum group elements are significantly more abundant in meteorites than terrestrial upper crustal rocks. Their presence in sediments is one line of evidence unanimously accepted by impact researchers.” One might say then that the discovery of PGEs at the YDB would constitute the extraordinary evidence that opponents have said they require in order to consider the impact hypothesis.
FEA reported modestly elevated iridium at their 10 YDB sites, as did Kennett et al. in their nanodiamond study. At Blackwater Draw, another group found that five of six spherules studied contained iridium at more than two hundred times its average abundance in the Earth’s crust. They found the same level of enrichment in osmium. Thus the question of elevated iridium at the YDB came to resemble that of the microspherules: some found it while other did not. But then attention switched to another of the PGEs.
Given the prominence of iridium as an extraterrestrial marker, researchers also looked for elevated concentrations of other members of the PGE group, including platinum. Paquay et al. (2009) had found weak peaks in iridium, osmium, and platinum at the YDB at Murray Springs and Lake Hind, Alberta, but concluded they were natural. A. V. Andronikov and colleagues found elevated Pt and other metals at several YDB sites in Europe and regarded them as extraterrestrial. In microspherules from Blackwater Draw, they found platinum at up to 900 times the crustal abundance. These tantalizing discoveries suggested that a more systematic study of Pt at YDB sites might yield important results.
ONCE DECLARED DEAD
The report from Bunch et al., mentioned in the last chapter, caught the attention of a research group from Harvard, leading them to write, “The impact hypothesis once declared dead, recently gained new support from the discovery of siliceous scoria-like objects (SLOs) with global distribution.”
Thus encouraged, the authors decided to test for PGE’s and other evidence in ice samples from a Greenland ice core. It is no accident that scientists have spent so much time and effort on the horn-of-plenty that the ice cores offer. They provide age resolution of a few years and preserve evidence of whatever was in the atmosphere at the time the original snow fell.
As shown in the chart below, the Harvard scientists found that iridium rose and fell (upper frame) through the YDB but with no particular pattern or outstanding spikes. But then they found something else, something that had never been found at any known impact crater: a spike in platinum at least 100 times its background level. The fine age-resolution possible from the ice cores showed that Pt concentrations rose over about 14 years, then fell back to background levels in about 7 years.
FIGURE 7:
A Greenland Ice Core shows a distinct spike in platinum at the YDB, but none in iridium. The blue line shows the change in temperature at the YD from oxygen isotope ratios.
As we have noted, the only way such chemical signatures can be present in the ice of Greenland, far from land, is if they come from dust transported from distant sources through the stratosphere. Scientists estimate the lifetime of stratospheric dust at about 5 years, close to the decay time of the Pt spike.
WIDESPREAD ANOMALY
The d
iscovery of the Pt spike in the Greenland ice naturally raised the question of whether it could be detected at continental YD sites and if so, whether it would coincide with the other event marker peaks at the YDB. In March 2017, a group led by Christopher Moore of the University of South Carolina answered yes, publishing, “Widespread platinum anomaly documented at the Younger Dryas onset in North American sedimentary sequences.” The authors first tested for a Pt spike at four of the best dated YDB sites, ones we have met before: Arlington Canyon on Santa Rosa Island, CA; Murray Springs, AZ; Blackwater Draw, NM; and Sheridan Cave, OH, with the results shown.
FIGURE 8:
Peaks in platinum abundance and other event markers at four YDB sites. The arrowhead symbol indicates where Clovis-age artifacts have been found.
At each of the four sites, a Pt peak far above background occurs precisely at the YDB. As shown, these peaks coincide with Clovis evidence and with similar peaks in microspherules and nanodiamonds.
Next the team extended the search to seven other YDB sites in the Southeastern U.S., ones that are poorly dated or even undated but whose stratigraphy and Clovis archeology are well-grounded. Again, they found a Pt peak at each. Pt concentrations varied widely, but averaged about 6.0 ppb, 12 times the crustal abundance.
These seven sites do not have the black mat, which could have helped to locate the YDB. But the presence of the Pt spike suggests that it could be used as an independent stratigraphic marker for the YDB, even in the absence of the black mat and of radiocarbon dating. In Chapter 10 we will look at the first use of the Pt layer in this way.
But what are we to make of the presence of Pt at the YDB? In a subsequent chapter we will encounter the late Wallace Broecker, widely regarded as the leading expert on the Pleistocene. The cause of the YD had been so elusive that Broecker had changed his mind several times. But as of 2010, he had rejected the YDIH. But then in a blog post, written after the discovery of the Pt peak in the Greenland ice, but before it had been reported as widespread, Broecker changed his mind again:
My take is that the Greenland platinum peak makes clear that an extraterrestrial impact occurred close to the onset of the YD. Perhaps the object was vaporized in the atmosphere accounting for the shape of the platinum peak.
RAINING DIAMONDS
By now the reader surely will not be surprised to learn that, like everything else about the YDIH, the presence and meaning of the ultramicroscopic diamonds continued to be controverted and complicated. Complicated because the nanodiamonds — whose size is measured in billionths of a meter — come in different forms that require special techniques to distinguish: cubic diamonds, lonsdaleite, n-diamond, i-carbon, diamond-like carbon nanoparticles, as well as graphene, a variety with a single layer of carbon atoms arranged in a hexagonal lattice. Thus even where nanodiamonds had been found, opponents could argue that the particular type was not evidence of an ET event.
As we saw, in 2009 Kennett and colleagues reported the presence of nanodiamonds at six widely separated YDB sites in the U.S. and Canada. A year later came the Nova program and a detailed article on the Greenland nanodiamonds, which include the rare hexagonal form lonsdaleite, known only from impact sites like Meteor Crater and laboratory experiments.
A 2010 paper in Science took the opposite view, as summed up it its title: “No evidence of nanodiamonds in Younger–Dryas sediments to support an impact event.” Two of their sites were from the Channel Islands, where as we have already seen, this group did not actually sample the YDB. The third was the Murray Springs site, where Haynes had introduced West to the YDB and the black mat. According to the abstract, only three years after the original PNAS article, the YDIH was already on its death bed:
Most evidence supporting [the YDIH] has been discredited except for reports of nanodiamonds (including the rare hexagonal polytype). Our results cast doubt upon one of the last widely discussed pieces of evidence supporting the YD impact hypothesis.
Nevertheless, reports of various forms of diamond at the YDB, including the diagnostic lonsdaleite, continued to appear. In 2011 a group reported that the YDB at Lommel, Belgium contains “cubic diamond nanoparticles in large numbers.” A team studying the YD in Central Mexico found nanodiamonds, carbon spherules, and magnetic spherules with rapid melting/quenching textures. These all peaked immediately beneath what appeared to be the black mat. In early 2014, another group confirmed finding a nanodiamond spike in the YDB at Bull Creek, OK.
Then came a 2014 article by Kinzie et al. titled: “Nanodiamond-Rich Layer across Three Continents Consistent with Major Cosmic Impact at 12,800 Cal BP.” They reported peaks in various types at 24 YDB sites in 10 Northern Hemisphere countries, identifying them using an alphabet soup of methods: “scanning electron microscopy, STEM, TEM, HRTEM, EDS, SAD, FFT, EELS, and EFTEM.” Below is a blowup of the chart from Kennett et al., showing the nanodiamond peak at Murray Springs, followed by one from Kinzie et al.
FIGURE 9:
The YDB nanodiamond and iridium peaks at Murray Springs from Kennett et al.
FIGURE 10:
Kinzie et al. replicate the YDB nanodiamond peak at Murray Springs. The shaded band is the YDB.
NANODIAMOND DATA: REPRODUCIBLE OR NOT?
The last word from opponents of the YDIH as this book is being written was a 2017 article titled, “Comprehensive analysis of nanodiamond evidence relating to the Younger Dryas Impact Hypothesis.” The authors had again looked for nanodiamonds in the suite of samples collected on Santa Rosa Island, but could find none. This led them to state that “There is no evidence to suggest a unique spike in the ‘nanodiamond’ concentration at the YDB layer.” In reports to the contrary, they said, adding “nanodiamonds were either misidentified and/or the data are not reproducible.” But Wolbach et al. (2020) state that the sample locations and diagrams in the Requiem and in the 2017 nanodiamond article “reveal that not a single sample was acquired from 12,800-year-old strata.” If so, as with the microspherules, it was the reported absence of nanodiamonds that proved irreproducible.
We will probably never know why a few could not find YDB microspherules and nanodiamonds while dozens of others have. But unless we want to say that the absence of evidence trumps multiple reports of positive evidence, we must accept that the microspherule and nanodiamond peaks exist and have been replicated many times over. This does not prove the YDIH, but removes the main evidence used against it.
10
WILDFIRES
CAUSE AND EFFECT
FEA reported “charcoal, soot, carbon spherules, and glass-like carbon” at various YDB sites, all of which they said, “suggest intense wildfires.” This was an important finding, for evidence of wildfires also occurs at three known impact craters and in the KT boundary layer. There the evidence includes peaks in physical objects, including “aciniform carbon” (resembling a microscopic bunch of grapes), as well as charcoal, carbon spherules, and a set of organic compounds that are diagnostic of fire. Obviously, if extensive wildfires and the resulting environmental damage had occurred at the time of the onset of the YD, that could help explain the megafaunal extinction and the Clovis decline.
In 2018, the Journal of Geology published two major review articles on the YDB wildfire evidence. The senior author in both was Wendy Wolbach of DePaul University, one of the original discoverers of aciniform carbon at the KTB. Her conclusions about wildfires there were confirmed in startling fashion by a 2019 article titled, “The First Day of the Cenozoic.”
FIGURE 11:
Wendy Wolbach in her laboratory
The first of the two articles (Wolbach I), set out to determine whether the chemical byproducts of fire, such as ammonium and nitrates, that scientists had previously reported in the Greenland ice cores coincided with the YDB. In so doing, they became the first to use the Pt peak as a stratigraphic marker for the YDB, as Moore et al. (2017) had proposed.
The authors first plotted the concentration of Pt in the GISP2 core, reported in the Harvard study, against that
of sea salt and continental dust, which had been found to rise sharply at the YDB, reflecting the increased wind speeds associated with the sudden temperature decline. They found that the Pt peak and the climate-related salt and dustiness coincided.
Next, they turned to the chemical fire indicators. After declining for several decades, ammonium, an aerosol diagnostic of fire, took a sharp jump just as the YDB began, then fell back, only to rise again over a century or so to two higher peaks, suggesting that wildfires continued for decades.
The Wolbach I authors went on to measure other fire indicators in the Greenland cores, as well from Antarctica and a Siberian ice core. They found that the YDB event as identified by the Pt peak, the YD cooling as located by oxygen isotope ratios, and a major episode of wildfires had occurred at the time, evidence of “cause and effect,” with the cause being “a cosmic impact.”
UNEXPLAINABLE BY NATURAL PROCESSES
Of course, the YD fires happened far from the icy wastes of Greenland, where there is nothing to burn. It is in the continental YDB record that scientists must look for the most critical evidence for widespread wildfires. This led to the second of the two articles with Wolbach as senior author: Wolbach II. The article reported charcoal and soot records from lakes, marine drill cores, and terrestrial YD sites. One benefit of the “Big Data” capabilities of the Internet is that scientists have been able to assemble huge databases, like the Global Charcoal Database, which provides a global paleofire dataset for researching sedimentary records of fire. The GCD allowed the Wolbach II authors to access data for nearly 9,000 samples from North, South, and Central America, Europe, and Western Asia, the continents known to have YDB sites.
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