No. 105: May-Jun 1996
Archeologists were initially attracted to Pedra Furada, in northeastern Brazil, by the area's rich and colorful rock art, some of which would not be allowed on the Internet! But it is not the rock art that is controversial about Pedra Furada; it is the 595 pieces of quartz selected by French archeologist N. Guidon. These bits of stone closely resemble humancrafted choppers, scrapers, and cutting tools. Indeed, if they had been found in more recent deposits, they would have been judged "man-made" by everyone. The trouble is that Guidon has dated them at 50,000 BP - a date mainstream archeologists cannot swallow. Any New World dates earlier than 12,000 BP, maybe 20,000 BP for a few daring souls, have to be erroneous.
How are the Pedra Furada chipped stones explained by mainstream archeologists? They are "geofacts, not artifacts. They were created when quartzite rocks were released by erosion and fell off cliffs to be smashed upon impact below. Gravity and not the human hand broke the quartz into pieces that just happen to look like prehistoric tools. F. Parenti, a coworker of Guidon, has tried to exorcise the geofact argument, which is used wherever tools are "too old", by showing that the 595 pieces of quartz have characteristics quite unlike those created by natural flaking.
The doubters are unswayed. You see, despite Parenti's analysis, there remains a minute chance that a falling rock will fracture into pieces, one of which will look human-made. Maybe only one falling rock in 10,000 will fracture "unnaturally;" make it one in 10,000,000; it doesn't matter. Anthropologist D. Meltzer writes:
"Of course, no matter how rare the chances, given sufficient time and raw material - Pedra Furada had plenty of both - nature can magnify even the slimmest odds to the point where geofacts occur in detectable frequencies."
In this argument, you see how our title "Darwinism in Archeology" came to be. Random events (rock falls or mutations) plus a sorting mechanism (human selection or natural selection) can produce geofacts or new species. This sort of explanatory mechanism can, in principle, explain just about anything!
(Meltzer, David; "Stones of Contention," New Scientist, p. 31, June 24, 1995.)
R. Dennell and L. Hurcombe, two archeologists faced with the geofact problem at their Pakistan dig, tried to solve it experimentally. They deliberately dropped quartzite rocks from heights onto hard surfaces. They concluded:
"While 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."
(Dennell, Robin, and Hurcombe, Linda; "Comment on Pedra Furada." Antiquity, 69:604, 1995.)