I talked once before about the “Clovis Comet” theory, which suggested the widespread extinctions of megafauna in North America at the end of the last ice age was caused by a large comet impact. At the same moment, the highly distinctive “Clovis” archaeological culture was terminated. It was suggested this comet might have either airburst or struck the ice sheets, in either case not causing a visible crater. However, abundant “nanodiamonds”, said to be highly diagnostic of an extraterrestrial impact, were found at a widespread boundary layer roughly associated with the end of Clovis – the start of the Younger Dryas cold period when the earth was suddenly thrust back into near-glacial conditions.
So, I said then and I’ll say again now: this theory didn’t pass the sniff test from the beginning because it is another example of “Clovis exceptionalism” – the skeptical leeway that the Clovis-First model of first peopling of the Americas has been afforded by segments of the archaeological community. No Clovis model was so implausible that it wasn’t given much respectful beard-stroking by the usual silverbacks.
Anyway, subsequent studies of the nanodiamonds and associated evidence have failed utterly to reproduce the findings. Now comes even more news that the comet theory is unsupported and that the original investigators may have mistaken nanodiamonds for, among other things . . . [drumroll] . . . “hardened faecal material from arthropods.”
As co-author Pinter says,
The [Younger Dryas] impact hypothesis was in trouble already before this latest finding. Many other lines of evidence — including: fullerenes, extraterrestrial forms of helium, purported spikes in radioactivity and iridium, and claims of unique spikes in magnetic meteorite particles — had already been discredited. According to Pinter, “nanodiamonds were the last man standing.” “We should always have a skeptical attitude to new theories and test them thoroughly,” Scott says, “and if the evidence goes against them they should be abandoned.”
To be fair, the original authors defend their discoveries still:
But the lead author of two earlier comet-impact papers, Douglas Kennett, an archaeologist at the University of Oregon in Eugene, calls the study “fundamentally flawed science”. “The claim we misidentified diamonds is false, misleading and incorrect,” he adds, although he declined to specify his objections.
And meanwhile, the pro-impact team claims to have found nanodiamonds in the Greenland Ice Sheet, though the date associations are admittedly unclear.
You know, it can be really hard to evaluate these kinds of arguments. What does the average archaeologist know about nanodiamonds? Can we, as outsiders, fairly evaluate competing papers, each of which has been peer reviewed? Perhaps not. So what then? “Argument by Authority” doesn’t really pass muster. And yet, and yet, — when you have a combination of an archaeologist claiming something about nanodiamonds, and someone with advanced training to study nanodiamonds claiming something different, namely that “your nanodiamonds are little tiny balls of shit“, surely that carries some weight.
No offence archaeologists, but almost all of us are jacks of all trades, and masters of none. It goes with the territory. I’m not super comfortable with this decision tree, but added to the original paper being a classic of the Clovis Exceptionalism genre, I’m putting my money on “no comet”. Clovis is still regionally interesting, but it will be understood, as I said previously, on human terms, not extraterrestrial ones.
Tyrone L. Daulton, Nicholas Pinter, and Andrew C. Scott 2010. No evidence of nanodiamonds in Younger–Dryas sediments to support an impact event. PNAS 2010 107(37) 16043-16047; doi:10.1073/pnas.1003904107
Andrew C. Scott et al. 2010. Fungus, not comet or catastrophe, accounts for carbonaceous spherules in the Younger Dryas “impact layer” Fungus, not comet or catastrophe, accounts for carbonaceous spherules in the Younger Dryas “impact layer”. GEOPHYSICAL RESEARCH LETTERS, VOL. 37, L14302, 5 PP., 2010 doi:10.1029/2010GL043345