Rejection of Holliday et al.'s comprehensive Gish gallop of the Younger Dryas impact hypothesis
Overall Summary
In previous blog posts I critiqued several sections of Holliday et al.'s (2023) review of the YDIH, highlighting its many errors. No refutation arguments were encountered at all. In fact, the main disagreements all seem to concern matters of interpretation, for example radiocarbon evidence. This is normal in science, and not a reason to claim "refutation".
Here I list the major errors encountered only in some of the sections of Holliday et al. I reviewed in this blog. Many of these points were made already by YDIH proponents in earlier papers, so it baffles me that they have been ignored by Holliday et al.. The remainder of Holliday et al. contains many more errors than in this list.
1. Holliday et al. frequently avoid addressing valid tests of the YDIH by falsely claiming such tests represent circular reasoning. If valid tests like these are routinely rejected, then their viewpoint becomes a self-fulfilling prophecy. Thus, they lack the basic logic required for properly testing the YDIH. This is very poor science on their behalf.
2. Holliday et al. fail to use the fundamental underpinning dogma of science, which is “model efficiency”, sometimes called “Occam’s razor”. Use of this principle can distinguish good science from bad science or even pseudoscience. The YDIH uses this principle; it is by far the simplest proposal that explains all the evidence, including the impact proxies and the apparently close timing of the impact with the YD climate change and associated megafaunal extinctions and human cultural changes.
3. Holliday et al. seem to misunderstand how science works. They frequently accuse the YDIH of inconsistencies, but their claims are spurious, often being based on articles that are not part of the scientific evidence base for the YDIH. They also consistently fail to take account of updates to the hypothesis that they know very well and which take into account new data and supersede older versions. They also fail to admit that speculation and error are part of the scientific process. Indeed, error correction is a sign of good science, not bad science.
4. Holliday et al. frequently criticize ideas that are not the YDIH or correspond to early versions of the YDIH without taking any updates into account. Their criticism therefore very often takes the form of "strawman" arguments, for example;
a. they consistently fail to acknowledge the preferred impact scenario consists of a multitude of comet fragments, mostly creating airbursts over several continents although ground impacts are not yet ruled out. This scenario is reiterated by Wolbach et al. (2018a,b) and Moore et al. (2023).
b. they consistently fail to use the YDB as a chronological datum against which archaeological evidence (such as Clovis artifacts and megafaunal remains) can be compared. Indeed, they make the opposite assumption, i.e. the YDB does not have the same date everywhere (and does not really exist). Thus, they do not assess the YDIH according to its own predictions and therefore do not actually test the YDIH properly at all. Again, they lack the logic to properly test the YDIH.
c. they frequently use alternative definitions for the YD onset. For example, they claim the YD onset is known from analysis of the deuterium excess in the NGRIP ice core (Steffensen et al., 2008). But this definition is contentious and is inconsistent with the proposed date of the impact obtained from radiocarbon data of the YDB.
d. Holliday et al. frequently misrepresent the YDIH. It does not claim that megafauna became extinct in an instant or that Clovis culture ended instantly at the impact. Instead, it predicts the impact had a significant effect on megafaunal populations and the Clovis culture and independent evidence supports this view.
5. Holliday et al. consistently fail to admit that the YDIH does not live or die by the evidence for its secondary effects. Thus, even if Clovis people were unaffected by the impact, it does not necessarily mean that the megafauna were unaffected. Again, their logic is inadequate.
6. Holliday et al. frequently fail to analyse uncertainty in experimental data properly. For example;
a. they fail to admit that the intrinsic uncertainty in individual radiocarbon measurements is not a good estimator for the true sample age uncertainty. This leads them to frequently underestimate the true uncertainty in radiocarbon samples, especially sites where only one radiocarbon measurement is made.
b. they rely heavily on Meltzer et al. (2014) to dispute the synchroneity of the YDB across several continents. Yet Meltzer et al. (2014) is obviously flawed since it does not take into account the uncertainty in its linear age-depth models. Associated with this, they also fail to admit that age-depth models should be created using uncalibrated radiocarbon data so that the uncertainty in the calibration curve is properly taken into account when their age-depth models are calibrated. Again, this is a very basic failing on their behalf and bad science. Meltzer et al. (2014) should be retracted.
c. they claim with certainty that the charcoal-rich Ussello/Finow horizon in western Europe is not synchronous. However, their claim fails to properly take into account the uncertainty in the radiocarbon data from these sites. In fact, these horizon layers are consistent with synchroneity.
d. they fail to realise that the conclusions of O’Keefe et al. (2023) regarding the megafaunal extirpation near the Rancho La Brea tar pits are unsafe due to incorrect interpretation of radiocarbon data. Their “almost certain” claim that these extirpations occur before the YD impact is inconsistent with the 1-sigma (68%) confidence interval used. At 2-sigma (95%), this extirpation is consistent with the YDIH.
7. Holliday et al. frequently demand evidence that is unreasonable. For example;
a. they frequently demand evidence for ground impacts when these are not required by the YDIH.
b. they frequently demand precise dates for the YDB. However, such demands are unreasonable - we must deal with the evidence that is found, not the evidence we would like to find. They also fail to admit that less precise data is still useful.
8. Holliday et al. frequently take inconsistent positions. For example;
a. they claim that microspherule evidence cannot be used to confirm an ET impact event by itself. Yet French and Koeberl (2010) suggests that this is indeed possible (note, C. Koeberl is a co-author of Holliday et al.). Moreover, Holliday et al. selectively quote French and Koeberl (2010); “Like other impact melts, droplet spherules generally preserve no evidence of shock processes or of their original ultrahigh-temperature origin….” Yet they must terminate their quote at this point because the next line in French and Koeberl (2010) reads “There are rare exceptions: inclusions of lechatelierite, coesite, and shocked zircon, which establish an impact origin directly…”. Lechatelierite has been found at several YDB sites.
b. they call coherent catastrophism “a speculative hypothesis that is unsupported by observational data and inconsistent with the cratering record” and “a preposterous fringe idea”. Yet they provide no evidence to support this view and fail to acknowledge that coherent catastrophism corresponds to the working model for the origin and evolution of the Taurid meteor stream among cometary scientists. At the same time they claim there is some truth to coherent catastrophism, but they disagree with an “extreme version” of it, without defining this version or providing any evidence to support their view. They further claim that results of the 2019 observational campaign on the Taurid resonant swarm contradict this model. However, this campaign never took place as intended and no papers have been written about it. Boslough (a co-author of Holliday et al.), at least, must know this since he "spearheaded" calls for this observational campaign. They further fail to mention that the existence of the Taurid meteor swarm was already confirmed by earlier observational campaigns.
c. they claim the Cape York meteorite could have created the GISP2 platinum signal, but this is pure speculation. They also claim the platinum signal requires a ground impact (without providing any supporting evidence), but fail to acknowledge that the Cape York meteorite is not associated with any crater.
9. Holliday et al. continue to support Daulton et al. (2010) regarding the the Arlington Canyon nanodiamond evidence. However, it is clear from the map coordinates in Scott et al. (2010) that Daulton et al. (2010) did not sample the YDB nor did they collect samples likely to contain nanodiamonds. Indeed, one site they sampled was over 7 km away from where Holliday et al. continue to insist they took the sample and another sample was too old by 500 years. Thus, Daulton et al. (2010) should be retracted. Furthermore, Holliday et al. consistently conflate this nanodiamond evidence with other nanodiamond evidence in later work by Daulton et al. (2017), thus obfuscating their argument.
10. Holliday et al. misreport the nanodiamond evidence from Bull Creek provided by Kennett et al. (2009) and then criticize YDIH proponents by claiming this evidence is inconsistent with the nanodiamond evidence in Bement et al. (2014). Clearly, any evidence can be claimed to be inconsistent if it is misreported. While Bement et al. (2014) likely contains some typos, it is consistent with Kennet et al. (2009).
11. HEA claim that ammonium and platinum abundances in the GISP2 ice core are not synchronous with the YD onset. But this view is based on misrepresentation of this data in Petaev et al. (2013) and ignores the correct plotting of this data highlighted by Sweatman (2021). They also ignore higher resolution data plotted in Wolbach (2018a).
12. Holliday et al. claim that a sudden “impact winter” is inconsistent with palaeoclimate data. However, they only use low-resolution data to make this claim when high-resolution sub-annual data is required.
13. Holliday et al. frequently conflate a cluster of megafaunal extinctions around the YD onset with other megafaunal extinctions over the last glacial cycle. The YDIH says nothing about these other extinction events.
14. Holliday et al. mistakenly claim that mixing of Clovis and other cultural artefacts contradicts the YDH. But, the YDIH makes no claims about other cultures and such mixing is commonplace in sediments.
15. Holliday et al. fail to understand fundamental problems in the work of Jorgeson et al. (2020,2022) on the synchroneity of the YDB across several continents which were pointed out by Sweatman (2021) and which make their conclusions unsupportable. In fact, Jorgeson et al.'s (2020,2022) work is not even a sensible line of research.
16. Holliday et al. frequently use ad hominem arguments that have no place in a scientific report. They also make frequent defamatory accusations unsupported by any evidence.
Conclusions
It is therefore clear that Holliday et al. is a Gish gallop; a long series of weak or false arguments designed to overwhelm an opponent.
HEA claim to refute the YDIH, but their claim should be rejected because;
1. They fail to provide any reasonable alternative explanation for the geochemical impact proxies found at 58 YDB sites (and counting) on at least four continents. All 58 sites show abundance peaks in materials such as exotic microspherules, platinum and nanodiamonds that are very likely synchronous. The most parsimonious explanation for this evidence is the YDB impact event. This evidence has been reproduced by independent researchers many times, so the possibility that it is all mistaken or manufactured is absurd.
2. They fail to show that any YDB site is inconsistent with synchroneity.
3. They fail to show that any Clovis artifacts are found above the YDB.
4. They fail to show that the timing of the Rancholabrean megafaunal extinctions are inconsistent with the YD onset. Indeed, multiple independent studies show they could be synchronous, including Boulanger et al. 2014, Villavicencio et al. 2015, Stewart et al. 2021 and O’Keefe et al. 2023.
5. Their work is yet another in a long line of papers with the apparent aim of suppressing work into the YDIH. Indeed, their title includes "comprehensive refutation" when there are no refutation arguments in their paper. It is for reasons such as these that Powell (2024) labelled their work, and that of others, "pseudoskepticism". It is bad science.
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