Coming at it from an astrophysical rather than an archaeological perspective, Neuhäuser and Neuhäuser (2022) published a brief but effective critique of Tankersley et al.’s (2022a) paper on the possible destruction of the archaeological Hopewell Culture by a comet airburst about 1600 years ago. Tankersley et al.’s (2022b) have a response, both in Nature Scientific Reports (see my own comment on the original article here).

The critique

In this new critique, Neuhäuser and Neuhäuser (N&N for convenience) argue that if airburst there was, the chemical evidence presented by Tankersley et al. is less consistent with a comet than with an asteroid, but that in any case there is little evidence of an airburst at all.

Second, and more importantly in my opinion, N&N establish quite clearly that, despite the claims in the original paper, there is no historical evidence of increased risk of cometary impact in the relevant period (1699-1567 years ago), and especially no evidence of a comet approaching Earth and suddenly disappearing (i.e. crashing into it).

As N&N point out, an approaching comet that crashed into the middle of North America would have been plainly and impressively visible all over the northern hemisphere for weeks at least. Since “all 1P/Halley perihelia of the last two millennia were noticed” and recorded, among many other events, it is highly unlikely that a much more impressive event would not appear in historical sources in East Asia and Europe.

Tankersley et al. quickly and prudently concede that given both the historical and chemical evidence, an asteroid airburst is more likely than a comet airburst in this case, but they don’t budge on the likelihood of some kind of impact destroying the Hopewell.

In a more archaeological vein, N&N critique Tankersley et al.’s identification of a Hopewell earthwork as a representation of the comet (or asteroid in Tankersley et al.’s revised hypothesis), and briefly point out that Hopewell trade in meteoritic material rather than an airburst could explain the chemical signatures reported in the original article.

Similarities in shape and symbolic representation are more difficult to grapple with than chemical residue from cosmic airbursts, but N&N’s argument on this is worth looking at. They reasonably note that what Tankersley et al. claim is a monumental representation of the comet at the Milford Earthworks is only a small part of a larger complex or works.

Figure 1: Survey map of Milford Earthworks by Major Isaac Roberdeau (1823), from https://earthworks.site/index.php/milford-earthworks

It is less obviously a picture of a comet (or of a Tunguska-like asteroid) if it is seen in its entire context (Figure 1). For instance, while the head of the comet (the circular work) is connected to the tail (the fan-shaped work), the head is also connected to another alley which leads to a larger sort of enclosure.

I will note in addition that there is another nearby circle (upper left side of Figure 1) connected to another alley, which leads to another square enclosure. In other words, there is a lot going on in that complex of earthworks, and any simple identification with a single historical event is uncertain to say the least.

The reply

In their reply, Tankersley et al. focus on conceding that an asteroid airburst is more likely than a comet airburst, and on establishing that the earthwork in question looks not only like a comet, but also very much like eyewitness drawings of the 1908 Tunguska asteroid airburst.

Tankersley et al. also spend some time discussing the Hopewell trade in meteoric material. They imply that the identification of Hopewell meteoric iron object with the 20k year old Brenham meteorite from Kansas is a simple assumption based on chronological coincidence, because Metz and Putnam first found meteoric material in Hopewell sites in 1882, around the same time that the Brenham material was discovered in Kansas.

In fact, as McCoy et al. (2017) put it “A definitive connection between Ohio Hopewell meteoritic iron and the Brenham, Kansas pallasite came with the advent of instrumental neutron activation analyses of meteoritic irons. By determining the trace element chemical composition of both the artifacts and metal within the Brenham meteorite, Wasson and Sedwick (1969) convincingly demonstrated a match.” So there is more to it than Tankersley et al. tell us.

Tankersley et al. then wonder why there are tiny fragments of meteorites on Hopewell sites if the presence of meteoric iron is due to trade in raw materials. We know that the Hopewell worked the material and made both tools and ornaments from it through hammering and other techniques, which would of course explain the presence of tiny fragments.

Lastly, Tankersley et al. wonder why some of the fragments are chemically different from the Brenham pallasite. We know that while the Brenham material was important to Hopewell trade, the network drew on numerous other meteoric sources, such as the Anoka, Minnesota meteorite (McCoy et al. 2017) and many others (Carr and Sears 1985), which explains the diversity, not to mention that there is considerable heterogeneity and variability within a single source such as Brenham.

In summary, N&N provide a couple more good reasons to doubt that there was an airburst (comet or asteroid) above the Hopewell area 1600 years ago.

References

Carr C and WG Sears 1985. Toward and analysis of the exchange of meteoric iron in the Middle Woodland, Southeastern Archaeology 4:79-92. https://www.jstor.org/stable/40712805

McCoy TJ, AE Marquardt, JT Wasson, RD Ash, EP Vicenzi 2017. The Anoka, Minnesota iron meteorite as parent to Hopewell meteoritic metal beads from Havana, Illinois, Journal of Archaeological Science https://doi.org/10.1016/j.jas.2017.03.003

Neuhäuser, R., DL Neuhäuser 2022. Arguments for a comet as cause of the Hopewell airburst are unsubstantiated. Sci Rep 12, 12090, https://doi.org/10.1038/s41598-022-16211-5

Tankersley, K.B., SD Meyers, SA Meyerset al 2022a. The Hopewell airburst event, 1699–1567 years ago (252–383 CE). Sci Rep 12, 1706, https://doi.org/10.1038/s41598-022-05758-y

Tankersley KB, SD Meyers, SA Meyers et al. 2022b. Reply to: Arguments for a comet as cause of the Hopewell airburst are unsubstantiated. Sci Rep 12, 12113 (2022b). https://doi.org/10.1038/s41598-022-16212-4

Wasson J, S Sedwick 1969. Possible Sources of Meteoritic Material from Hopewell Indian Burial Mounds. Nature 222:22–24 https://doi.org/10.1038/222022a0

One thought on “Hopewell airburst event news : Tankersley et al. retreat from comet to asteroid hypothesis

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