Wonderwerk Cave's located where there's a diamond labelled WK in the heart of the photomap below.
|After Henshilwood and Dubreuil. 2011. The Still Bay and Howiesons Poort, 77–59 ka: Symbolic Material Culture and the Evolution of the Mind during the African Middle Stone Age. Current Anthropology, 52, 361-400.|
I may not be a geochemist or a micromorphologist, but I am sentient. And when I see an extraordinary claim... Well, you know how it goes. I do what I can to learn enough to achieve a minimal level of critical ability and then assess the extent to which the claimants attempt--successfully--to rule out natural processes. In the case of this Lower Palaeolithic Prometheus, the chemistry and the technology are my stretch domains. However, logical argumentation is my comfort zone. So, with a little Googling and some gumption, that's where I'm headed today.
I'm talking about a paper, recently published in PNAS.
Berna, et al. 2012. Microstratigraphic evidence of in situ fire in the Acheulean strata of Wonderwerk Cave, Northern Cape province, South Africa. PNAS April 2, 2012.
Published online before print April 2, 2012, doi: 10.1073/pnas.1117620109
[Hey Rocky! Watch me pull a(nother) rabbit outa my hat!]The authors contend that their findings provide 'the earliest secure evidence for burning in an archaeological context.' [At this point all of you readers will, automaton-like, voice the pre-eminent subversive question: 'Did they rule out natural causes before imputing their discoveries to humans or other hominids?' Pat, pat. Good little Subversive! Here's a biscuit.]
|Paul Goldberg and Francesco Berna|
I've been seeing similar claims from Middle Palaeolithic contexts since the late 80s, almost always accompanied by Paul Goldberg's micromorphological analysis and Steve Weiner's or Francesco Berna's Fourier Transform Infrared Spectrometry of the phosphate minerals. I've been skeptical all along, which is my proclivity, nevertheless I've been reluctant to mount a critique. Until now. The stakes have finally grown too great to remain silent.
I've known Paul since the mid 80s. We spent time together at Keatley Creek, in B.C. Then after a month-long stint at Kebara Cave in '89 he toured me around the south of Israel, at which time I met Arlene Rosen, and during which I got hotter than I can remember ever being before or since, in the Dead Sea Depression.
I had a job once when I was at SFU. I was to impregnate a bunch of micromorphology samples from the Keatley Creek site with fibreglass resin. Unfortunately the vacuum chamber I was using was a little short of breath and some of the samples turned out crap. But that's beside the point. [Really, Rob? What IS the point of all this reminiscing?] The point is that I know Paul. I know his work. He [quite literally] wrote the book on the micromorphological study of archaeological sediments. I accept his findings. Nevertheless, when all's said and done in the authors' analysis of Wonderwerk Cave, it's not Paul's micro-study that's at fault. Nor is it Francesco Berna's FTIS results. It's the way they argue on the basis of their findings at which I baulk.
|Wonderwerk Cave [er, the entrance, at any rate]|
At Wonderwerk a deeply stratified deposit contains an abundance of what are referred to as 'rubefied' [or reddened] sediments. This should come as no surprise, since the deposits are made up almost exclusively of aeolian sand that's encrusted with iron oxide [=rust]. However, there are also places where the excavators recovered floral ash and burned faunal fragments. Bat caves are capable of building up prodigious deposits of guano--they've been mined, historically, for fertilizer--and those deposits are known to burst into flame spontaneously. So, why couldn't the fire-affected traces be the result of naturally occurring fire(s)? After all, the authors report no features at the site that might be construed as hearths.
To their credit, Berna et al. have succeeded in mounting a convincing argument that enough heat was generated here and there in the deposits to have altered the chemistry of plant and animal remains, leaving ash and burned bone and plant remains. They infer that temperatures higher than 550 °C were not in evidence.
They base their refutation of the spontaneous combustion argument on the work of one geologist from one cave in Romania, Cioclovina. The authors conclude that natural, spontaneous combustion of bat guano had not occurred in Wonderwerk Cave.
This is the shape their argument takes
a) When bat guano spontaneously combusts it transforms some of the guano's aluminum phosphates into two very rare forms: Berlinite and hydroxylellestadite.
b) FTIS found no Berlinite or hydroxylellestadite in the samples from Wonderwerk cave.
c) Therefore no spontaneous combustion of bat guano can explain the fire-affected flora and fauna in the cave.Here are some brutal facts up against which this argument cannot stand.
1. The discovery of Berlinite in unconsolidated sediments at Cioclovina Cave is unique. All the rest of the Berlinite known in the world occurs in the form of ore. At Cioclovina the Berlinite formed during one or more episodes of very high temperature combustion of bat guano--so hot, in fact, that a stratum of sediment was fused solid (Onac, Effenberger and Breban, High-temperature and “exotic” minerals from the Cioclovina Cave, Romania: a review, Studia Universitatis Babeş-Bolyai, Geologia, 52, 3- 10, 2007).
2. The discovery of hydroxylellestadite at Cioclovina Cave is equally unique.
3. Berlinite forms at 583 °C (http://www.mindat.org/min-633.html) [I was able to find no empirical data on the temperature at which hydroxylellestadite forms].
4. Bat guano degrades normally to form phosphate minerals including, but not limited to Brushite, ardealite, monetite, Taranakite, variscite, crandalite, sasaite, hydroxylapatite, whitlockite, vivianite, Hopite, sampleite, and churchite (Encyclopedia of Caves, 2nd Edition, by W.B. White and D.C. Culver, Academic Press, 2012).
5. Under great pressure and very high temperatures bat guano will form Arnemhite, Berlinite, and Pyrocoproite [and is now known to form hydroxylellestadite] (Encyclopedia of Caves, 2nd Edition, by W.B. White and D.C. Culver, Academic Press, 2012).Berna et al. have argued that because no Berlinite was found at Wonderwerk Cave they were able to rule out spontaneous combustion of bat guano at the source of the heat that altered the floral and faunal remains they examined. However, the same authors have determined that at Wonderwerk Cave combustion occurred at temperatures below 550 °C. Mineral science teaches us that Berlinite and hydroxylellestadite form at temperatures at or above 583 °C. No such temperature was reached in Wonderwerk Cave. Ipso facto, prest-o change-o, Berna et al. have erred in presuming that Berlinite would have formed at Wonderwerk Cave.
Berna et al. state the following
Moreover, micromorphology and mFTIR did not show evidence for remains of guano and/or high-temperature phosphate mineral phases (i.e., berlinite and hydroxylellestadite); these minerals characteristically form during spontaneous combustion of bat guano—a rare event but one documented inside caves.I would be verrry interested to see the complete results of the FTIS analysis of the Wonderwerk sediments. Given that there are Chiroptera remains in the sequence it's likely that there would have been at least some guano lying around at some time during the hominid use of the the cave. And, as you prolly know, bats are known to aggregate in the gabillions in some caves. I'd be surprised to find NO evidence of the phosphate minerals that would belie the earlier presence of bat guano--burned or not.
So, there you have it, Paul and Francesco [we've never actually met, Francesco, but I hope you won't mind me using your first name--they always told me I should act like a grown-up once I got my Ph.D., and so I try now and again to follow their advice].
The gauntlet is thrown down.
Gentlemen! Show me the monetite!