14 October 2013
Peering inside prehistoric clay balls
Archaeologists are using CT scanning and 3D modelling to crack a lost prehistoric code hidden inside clay balls, dating to some 5,500 years ago, found in Mesopotamia. These clay balls may represent the world's "very first data storage system," at least the first that scientists know of, said Christopher Woods, a professor at the University of Chicago's Oriental Institute.
The balls, often called 'envelopes' by researchers, were sealed and contain tokens in a variety of geometric shapes - the balls varying from golf ball-size to baseball-size. Only about 150 intact examples survive worldwide today. Researchers have long believed these clay balls were used to record economic transactions. How these devices would have worked in prehistoric times, before the invention of writing, is a mystery.
The researchers used high-resolution CT scans and 3D modeling to look inside more than 20 examples that were excavated at the site of Choga Mish, in western Iran, in the late 1960s. They were created about 5,500 years ago at a time when early cities were flourishing in Mesopotamia.
The CT scans revealed that some of the balls have tiny channels, 1-2mm across, crisscrossing them. Woods said he's not certain what they were used for, but speculates the balls contained fine threads that connected together on the outside. These threads could have held labels, perhaps made out of wax, which reflected the tokens within the clay balls. The tokens within the balls come in 14 different shapes, the researchers found. These shapes would have conveyed numbers connected to a variety of metrological systems used in counting different types of commodities, Woods suggested.
The researchers, however, were perplexed when their CT scans found one clay ball containing tokens made of a low-density material, likely bitumen. 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. Woods said that the bitumen tokens may represent a divergent accounting practice, or, perhaps even, that the transaction recorded involved bitumen.
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, while the polar seals 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.
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.
The amount of detail the scientists gleaned from the CT scans and 3D modeling was extraordinary; "We can learn more about these artifacts by non-destructive testing than we could by physically opening the envelopes," Woods said.
Edited from LiveScience (10 October 2013)