Comment on Pedra Furada.

Dennell, Robin ; Hurcombe, Linda

An issue in the status of the flaked stones from Pedra Furada, Brazil is whether they are artefacts or fractures naturally made on falling stone. An experiment by other researchers is pertinent.

We offer a comment on the suggestion that seemingly-convincing quartzite artefacts could have been produced by stones falling from the cliffs above the cave of Pedra Furada, Brazil. Our comments stem from our own attempts in the field to demonstrate that flaked pieces of quartzite from a 2-million-year-old horizon at Riwat (Pakistan) that are, in our opinion, intentionally-struck were not the result of stones falling naturally on to other stones or a similarly hard surface.

The experiment is as follows, should anyone wish to replicate it: as principal investigator (PI) take 100 quartzite cobbles/unflaked stone nodules that are 5-15 cm (3 [inches]-6 [inches]) long (i.e. the size that could have been used for making stone tools); one concrete, steeply-sloping embankment around 12-15 m high; and (indispensable) one gullible collaborator (GC). Place the GC at the bottom of the embankment to collect the resulting fractured stones. Start by throwing each stone as high in the air as possible, so that it strikes the embankment at least once when it falls. As the experiment progresses (and no fractures occur), proceed by throwing the stones as hard as possible on to the concrete embankment. Advise (persuasively) the GC to take cover as the stones are hurled down, but tell him/her to be absolutely sure to retrieve each stone as it whizzes by. End (in complete frustration) by offering to change places with the GC to show that no personal feelings are involved, and see if the GC can induce any flaking in this manner!

The point of this is that we tried to flake quartzite by simulating stones dropping down several metres on to a hard surface. Not a single one fractured in any way whatsoever. The experiment we conducted suited our particular problem; it would be easier to fracture angular fragments than rounded cobbles, and more brittle lithic materials would fracture more easily. The quartzite used for making stone tools in Pakistan may be unusually hard, and that in Brazil unusually soft: however, in our experience, it seems highly improbable that anything resembling a convincing quartzite assemblage could result from stones falling down a cliff or chute. Whilst conceding that had we conducted the experiment with a thousand, ten thousand, or a hundred thousand stones, a few might have fractures, we would nevertheless maintain that the chances of any showing multiple, multi-directional flaking and all with bulbs of percussion are as remote as the proverbial monkey typing Shakespeare. Better, perhaps, to monitor the original flaking (if any) of the quartzite nodules at Pedra Furada before they might have fallen down the cliff above the cave. If a pile of fractured and unfractured stone had accumulated at the base of a chute, then the falling stones might result in secondary flaking of some of the material at the base, but these would largely be snap or half-moon breaks rather than invasive feather-terminated scars.