The tokens, in this instance, had air bubbles around them, suggesting they were wrapped in cloth before being put in the ball, the cloth disintegrating over time. In addition, it appears that a liquid, likely liquid bitumen, was poured over the tokens after they were inserted into the balls. What someone was trying to communicate by creating such tokens is unknown.
"That's a mystery," Woods told LiveScience in an interview. "I don't really have a good answer for that," he said, adding that the bitumen tokens may represent a divergent accounting practice, or, perhaps even, that the transaction recorded involved bitumen.
In ancient Mesopotamia bitumen was used as an adhesive and to waterproof things like baskets, boats and the foundations of buildings, Woods said. (In Photos: Treasures from Mesopotamia)
Cracking the prehistoric code
All of the clay balls contain, on the outside, one "equatorial" seal (running through the middle) and quite often two "polar" seals, running above and below.
The equatorial seals tend to be unique and more complex containing what appear to be mythological motifs; for instance a ball from the Louvre Museum shows human figures fighting what appear to be serpents. The polar seals, on the other hand, are repeated more often and tend to have simpler geometric motifs.
Based on this evidence, Woods hypothesizes the seal in the middle represents the "buyer" or recipient; the polar seals would represent the "seller" or distributor and perhaps third parties who would have participated in the transaction or acted as witnesses.
Many people would have acted as the buyers, but only a limited number of sellers or distributors would have been around to transact business with, explaining why the polar seals are repeated more often.
After a transaction of some importance was complete, one of these clay devices was created to serve as a "receipt" of sorts for the seller, as a record of what was expended. "There's a greater necessity to keep track of things that have been expended than things that are on hand," Woods said in the lecture.
Deciphering what transaction each clay ball represented is a trickier problem. Woods suspects the tokens represent numbers and metrical units. It's possible that, through the different token shapes, people in prehistoric times communicated numbers and units in a way similar to how the first scribes did 200 years later when writing was invented. If that's the case, Woods and other scientists may be able, in time, to crack the code by uncovering how token types cluster and vary.
"If they are, then there is at least some hope of deciphering the envelopes and with it uncovering the earliest evidence for complex numerical literacy," Woods said.
The amount of detail the scientists gleaned from the CT scans and 3D modeling was extraordinary, Woods said during the lecture. "We can learn more about these artifacts by non-destructive testing than we could by physically opening the envelopes," he said.
Woods will publish the full research results in the future and plans to put the images and 3D models online.
To peer inside the balls Woods worked with Jeffrey Diehm, who arranged for them to be CT scanned on a state-of-the-art industrial scanner (which is better suited for this work than a medical version), and Jim Topich, who had the CT images converted into detailed, dissectible, 3D models. Diehm was with North Star Imaging in Minnesota at the time the scans were done in 2011 (he is now the managing director of Avonix Imaging) and Topich is director of engineering and design at Kinetic Vision in Cincinnati.
The Royal Ontario Museum has a special exhibition on Mesopotamia that runs to Jan. 5, 2014. Woods' presentation is part of a lecture series that is appearing along with it.
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