His objection to the published science and data of the Comet Research Group is curious, since our work validates much of his unpublished speculation concerning catastrophe at the Pleistocene-Holocene transition. This dynamic is disappointing because those working to reveal the true record should find some common cause. Unfortunately, Schoch has never reached out to our researchers in order to work through and address his criticisms.
So, the CRG is taking the opportunity here on the Tusk and elsewhere to rebut Dr. Schoch's critique in the hope that he will carefully re-consider his position, which seems entirely based on the on the faulty work of our critics which are his too.
In his commentary, Dr. Schoch mentions Tian et al. (2012, PNAS), who confirmed our group's discovery of nanodiamonds in Europe in the YDB impact layer in Belgium, exactly where we said they were. That group also reported that no such particles are found in the overlying silt and clay or in the underlying fine sands. This is an important point; the nanodiamonds are rare and found only in the YDB layer, making them highly unusual. Furthermore, the nanodiamonds are found exclusively in the same layer that contains melted iron spherules, high-temperature meltglass, and the platinum-group elements, iridium and osmium, none of which are found above and below the YDB layer, also making them rare. Tian et al. admitted that they could not explain how the nanodiamonds got there, stating "that their exact origin remains unclear," but, it is important to note, they did not specifically exclude the possibility of an impact - they just said the origin is unclear. Critics of the YDB impact event have used that paper as evidence that YDB nanodiamonds were not caused by an impact, even though the paper makes no such claim and presents no such evidence. For details, see here.
It is easy for critics to make dismissive claims that YDB nanodiamonds were caused by something else besides an impact, such as forest fires, but those critics have yet to provide a single bit of evidence that forest fires, or any natural mechanism other than an impact event, are capable of producing nanodiamonds. In fact, the opposite is true - there is ample evidence that forest fires cannot produce nanodiamonds. In various industries, nanodiamonds are a highly valuable commodity and are used in many products, including lubricants and polishing compounds. Research costing many millions of dollars has been conducted in hundreds of laboratories to find ways to make nanodiamonds, and not one of those ways includes setting a tree on fire - it simply is impossible under normal conditions. However, it is possible to make nanodiamonds in the laboratory under very unusual conditions that mimic a cosmic impact event. In summary, it makes no scientific sense to claim that YDB nanodiamonds formed in forest fires, when there is no evidence for that, and to claim that they did not form by a cosmic impact event, when there is ample evidence that nanodiamonds can form that way and have done so frequently in the past.
Furthermore, we and other scientists have searched through many layers of rock and sediment, spanning millions of years, but have found similar nanodiamonds only in those layers deposited by cosmic impact events (Kennett et al., 2009, PNAS; Kinzie et al. 2014, Journal of Geology). The most famous discovery of similar nanodiamonds is in the layer deposited by the asteroid that killed the dinosaurs 65 million years ago, called the KPg boundary layer. Those KPg nanodiamonds were found only in the thin layer produced by the impact event and were not found in layers above and below it, even though there was ample evidence for normal wildfires in those layers. In other words, they were extraordinarily rare. The KPg nanodiamonds are structurally and chemically identical to those in the 12,800-year-old YDB layer.
Kennett et al. (2009, PNAS) published a paper on a type of nanodiamonds called lonsdaleite. Dr. Schoch cited Boslough et al. (2012, Geophysical Monograph Series), who claimed that all of the supposed "lonsdaleite" is not lonsdaleite at all, but rather a misidentification of another material. After Dr. Schoch published his comments, that statement by Boslough et al. was thoroughly refuted in a paper published by Kinzie et al. (2014, Journal of Geology), who reported the following: "Potential YDB lonsdaleite crystals have been identified and analyzed with HRTEM, FFT, SAD, and EDS [analytical techniques involving an electron microscope]....All the lonsdaleite-like crystals observed contain only carbon [as expected for diamonds]....All measured lattice planes are consistent with lonsdaleite."
Regarding another proxy, microspherules, Dr. Schoch cites Pigati et al. (2012, PNAS), who claimed that elevated concentrations of such spherules"arise from processes common to wetland systems, and not a catastrophic extraterrestrial impact event." The problem is that the Pigati study contains major mistakes. They collected most of their microspherules from sediment near South American volcanoes, which are well known to produce millions of non-impact glassy spherules. An electron microscope (SEM) can quickly and easily reveal the difference between impact spherules, volcanic spherules, and other types of non-impact spherules. And yet, the Pigati group simply neglected to perform those analyses, even though the Comet Research Group has repeatedly specified in our papers that SEM work is crucial, and without it, any study of spherules, including theirs, is meaningless. The Pigati group simply found normal volcanic spherules and claimed that they are identical to the impact spherules produced by the YDB event. That makes no more sense than claiming a golf ball is identical to a baseball.
Dr. Schoch further discusses the impact spherules reported by Wittke et al. (2013, PNAS), who found 10 million tonnes of them scattered across four continents. In his online article, Dr. Schoch cited research by Thy et al. (2015, Jour. Archaeological Science) and claimed that "these supposed 'impact spherules' were of ancient human origin (for instance, produced when buildings were destroyed in fires)." It is clear from Dr. Schoch's comments that he simply accepted some of the results from Thy et al. uncritically, but also that he over-interpreted them. Thy et al. clearly state that their results "do not necessarily discredit the Younger Dryas impact hypothesis." Any time that a new hypothesis is presented, it is necessary, of course, to ask whether the new evidence is accurate or flawed. However, it is also necessary to critically ask whether or not critics of the hypothesis present contradictory evidence and conclusions that are accurate and unbiased. Unfortunately, Dr. Schoch, as well as others, simply accepted the negative conclusions from some of these critics without adequately questioning them.
Stereomicroscopic images of various classes of micrometeorites.
Some of the conclusions by Thy et al. are simply incorrect. The biggest mistake they made is to ignore previously published information about abnormally high melting temperatures of spherules and meltglass from Syria and the United States. Both Wittke et al. and Bunch et al. (2012, PNAS) presented abundant evidence of meltglass and spherules that had been subjected to temperatures of as high as 2000°C, close to the melting point of quartz grains and chromite grains. There is simply no evidence of any kind that house fires can reach these temperatures, a point agreed to by Thy et al., who stated that the maximum temperatures of the house fire spherules they analyzed was only 1200°C, well below the temperature of 1750-2000°C found by our group. Furthermore, Thy et al. acknowledge that their house-fire hypothesis does not apply to meltglass found at two other YDB sites, where they acknowledge that temperatures ranged up to 1750°C and they acknowledge that they cannot explain these high temperatures. In summary, the difference between house fire spherules and impact spherules can easily and quickly be determined by adequate analyses with an electron microscope. The house fire spherules that Thy et al. found cannot be used to prove that impact spherules do not exist, and in fact, house fires are predicted to have occurred in association with the impact event in Syria. Thus, it is reasonable to expect that both types of spherules would exist together.
Dr. Schoch also discussed the results of Meltzer et al. (2014, PNAS) who concluded: "Only 3 of the 29 [YDB] sites fall within the temporal window of the YD onset as defined by YDIH [Younger Dryas Impact Hypothesis] proponents." Dr. Schoch uncritically accepted those results without asking whether that conclusion might be incorrect, and once again, there is ample evidence that those authors were wrong. A subsequent paper by Kennett et al. (2015, PNAS) revealed numerous, fatal errors in the calculations presented by Meltzer at al., meaning that their conclusions are simply invalid. Kennett et al. reported the following: "Bayesian chronological modeling [a highly sophisticated statistical technique] was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled YDB age range for this event of 12,835 - 12,735 Cal B.P. at 95% probability. This range overlaps that of a peak in extraterrestrial platinum in the Greenland Ice Sheet and of the earliest age of the Younger Dryas climate episode in six proxy records, suggesting a causal connection between the YDB impact event and the Younger Dryas." These results directly contradict the results of Meltzer et al.
Even though Bayesian analysis has become the new standard and is widely used by many scientists, Dr. Schoch argues against this conclusion, writing that "one can take issue with the appropriateness of applying Bayesian analyses," although he offers no evidence to support his position. Refuting that claim, Kennett et al. also used non-Bayesian analysis for the YDB sites and reported that "19 of 23 dates (83%) overlap from 12,840 to 12,805 Cal B.P.... This indicates that the results from simply calibrating a group of YDB dates are not substantially different from using Bayesian-modeling for YDB dates." In summary, criticisms of the timing of the YDB event simply do not stand up to scrutiny.
Dr. Schoch also discussed a YDB-age platinum anomaly found in a Greenland ice core by Petaev et al. (2013, PNAS), who concluded that a major cosmic impact event occurred over the Greenland ice sheet at the onset of the Younger Dryas. Dr. Schoch speculated that the platinum anomaly could have resulted from the eruption of the Laacher See volcano (Germany) around 12,900 years ago, but this suggestion has been refuted by Kinzie et al. (2014, Journal of Geology), who found no YDB spherules or nanodiamonds in the Laacher See ash layer, which lies below the YDB layer at some of the sites our group tested. In addition, our group recently tested the Laacher See ash layer and found no detectable platinum, meaning that the Laacher See eruption could not be the source of the platinum found in Greenland. Instead, the best explanation is an extraterrestrial impact event, as proposed by Petaev et al.
Dr. Schoch also speculated that the source of the platinum may be a relatively small, non-cataclysmic meteorite impact, but this is refuted by the original research group, Petaev et al., who discovered that the platinum deposition spanned about 21 years, meaning that the platinum must have been injected high into the atmosphere, after which it slowly rained down onto the Greenland ice sheet during the following two decades. Such long-term fallout could not result from a small impact, but rather requires a major impact event with widespread effects.
In support of the idea that YDB platinum is widespread and resulted from a major impact, Andronikov et al. (2016, Geograﬁska Annaler) found very high concentrations of platinum and iridium in melted YDB spherules from Blackwater Draw, New Mexico, more than 5000 km away from the platinum site in Greenland. In addition, Andronikov et al (2014, Doklady Earth Sciences; 2015, Quaternary International) investigated sediments from several lakes in NW Russia near Finland and Lithuania, and found sharp-peaked platinum anomalies in the YDB layer, along with other meteoritic elements such as nickel, chromium, and iridium. These sites are more than 9000 km away from the YDB platinum site in New Mexico, indicating that the platinum was deposited by a very large YDB impact event, not a small one.
Also in his online statement, Dr. Schoch cites Boslough et al. (2012) as claiming that "another argument against the impact hypothesis is that no crater (or craters) has yet been definitively identified as dating to circa 12,900 years ago." However, that claim by Boslough et al. is simply incorrect. Some of the largest known impacts on Earth have left no crater, including the Australasian Tektite Field, which spread molten pieces of glass across 10% of the planet from China to India, as well as the Libyan Desert Glass field, which spread molten pieces of glass across wide areas of the Egyptian desert without leaving a crater. The lack of a crater simply cannot be used to prove that an impact event did not occur.
On the positive side, Dr. Schoch is impartial in discussing the possibility that the impactor exploded in the atmosphere, breaking up into numerous fragments that cratered into the glacial ice sheets, which subsequently melted, thus destroying the ice-walled craters. However, he again cites Boslough et al. (2012), who analyzed this possibility and concluded that "consideration of basic laws of physics indicate that such a fragmentation or high-altitude airburst event ... would lie outside any realistic range of probability, and therefore did not occur during the YD as described by Firestone et al." This argument by Boslough et al. is completely spurious, because those authors are arguing against a scenario that they made up, namely that the initial fragmentation of the comet took place in the atmosphere. Instead, we have consistently and very clearly stated the hypothesis that fragmentation of the giant comet took place in deep space long before hitting Earth.
Far from being "outside any realistic range of probability," comets break up into multiple pieces in deep space exceedingly often. For example, meteor showers are the remnants of broken-up comets, and Earth regularly is hit by 109 meteor showers every year, averaging 2 collisions with those streams each week. We know them by such names as the Taurids, beta-Taurids, Geminids, and Perseids. Furthermore, 50 new, broken-up comets have been discovered in the last 150 years, for an average of a new one every three years. One of those, Comet Shoemaker-Levy, broke up into as many as 21 pieces and crashed into Jupiter in 1994, leaving a dark scar that was wider than the Earth. If Comet Shoemaker-Levy had hit Earth, it would have created catastrophic destruction on a hemispheric scale. So, in summary, far from being unlikely, it is exceedingly common for broken-up comets to hit Earth - they do so at least 109 times a year.
Shifting our attention from the beginning of the Younger Dryas 12,800 years ago to the end of the Younger Dryas 11,700 years ago, Dr. Schoch wrote that "in my assessment the evidence points to a major solar outburst (or series of closely spaced solar outbursts) at that time." In our proposed scenario, if a giant broken-up comet impacted Earth, parts of it could also have crashed into the sun, potentially triggering massive solar flares. Although there is no strong evidence either for or against, we feel that the hypothesis implicating solar flares in the abrupt ending of the Younger Dryas is plausible enough to warrant further investigation, although it also is possible that oceanic impacts by the same group of comet fragments may have occurred 11,700 years ago.
To be clear, Dr. Schoch does not propose a solar outburst at the beginning of the Younger Dryas, only the end of it. However, we wish to point out that even if a major solar outburst occurred 12,800 years ago, such an event could not have melted rocks on Earth's surface to 2000°C or formed nanodiamonds and other high-temperature proxies. This is because solar outbursts produce huge quantities of high-energy protons, electrons, and ions that bombard Earth's magnetic field and ozone layer, but those particles are not energetic enough to start forest fires, let alone melt rocks. Thus, the evidence from 12,800 years ago still requires a major cosmic impact event.
In closing, it is crucial to re-emphasize that the YDB layer, dated to approximately 12,800 years ago, contains a unique assemblage of exotic proxies that has never been reported to result from solar flares, wildfires, human activities, volcanism, or any other known natural terrestrial process. Instead, the only process known to produce that full range of proxies is a cosmic impact event. Thus, unless some new evidence comes to light that has never been seen before, the best current explanation for the proxies in the YDB layer is a cosmic impact event. For detailed information on the Younger Dryas impact hypothesis, see the Comet Research Group.
From the Comet Research Group