P200 Introduction to Prehistoric Archaeology
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 P200 Introduction to Prehistoric Archaeology
P200 Home Page | Syllabus | Reading schedule| Lecture Notes | Assignments

Finding and dating the first stone tools

Last time I left you with a puzzle -- Dart's "Osteo-donto-keratic" culture. The problem with Dart's interpretation was that it was largely circumstantial -- no direct evidence that the hominids had actually made or used any of the bones -- and Bob Brain (video) demonstrated that the australopithecines in the caves were more likely to have been the hunted, not hunters, although some of the bones showed wear patterns suggesting their use as digging tools.

So -- today we'll turn our attention to East Africa and sites in the Great Rift Valley... a region that has been called the Klondyke of human evolution because so many fossils and sites have been preserved there. What makes it so unique? Unlike South Africa, which preserves little "rubble traps" of sediment cemented together as breccia in isolated caves, the geology of the Rift valley preserves remains of ancient times in the sediments of lakes and rivers. The movement of geological plates in East Africa has caused the continent to uplift and crack open through faulting. (video) Fault troughs form valleys, which fill with rain water and runoff from the highlands... creating lowland lake basins. Such basins are great places for fossils and ancient garbage to be buried and preserved.

BURIAL is the key to preservation! How do you become a fossil? Get buried! How do you preserve your garbage for posterity? Bury it! (Remember the "privies" at the Five Points site in NYC?) Burial can occur due to natural causes ... the wind and the rain... (ash from a volcanic eruption or dust blown by wind, silts and clays washed in by a river) or cultural causes (your house can collapse on top of you, you can be dumped in a pit, or layed to rest in a cemetary plot) (slides)

Layer upon layer of sediments have stacked up in the East African Rift... forming deep stratigraphic sequences, with the deposits lowest in the sequence being the oldest ("Law of superposition"). Continuing earthquakes and geological faults in the region have exposed these ancient layers on the modern landsurface.... erosion washes away ancient sediments and lets anthropologists go prospecting for ancient remains along modern hillsides.

Radiometric techniques based on measuring the decay rates of unstable isotopes, like potassium-40 (K-40) allow archaeologists to date the age of the formation of volcanic rocks, using the potassium-argon (or Argon-Argon) technique.

Other methods for correlating sites of known-age include correlations based on paleomagnetic polarity (normal or reversed) and biostratigraphic correlations.

Important question:

It was in just such a dry, eroded landscape in the Rift Valley of Ethiopia that archaeologist Dr. Sileshi Semaw discovered some broken rocks at a site called Gona that he claims are the world's oldest known artifacts

-- stone tools, over two and a half million years old (2.6 mya). (stone tool demonstration)

Two important questions:

 

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Last updated: 1 Februaryl, 2000
URL: http://www.indiana.edu/~origins/teach/p200/xxx.html
Comments: sept@indiana.edu
Copyright Jeanne Sept 1998 : do not cite without permission