Non-technical Summary and 3 Case Studies
MURR's Archaeometry Lab: A Non-technical Summary
At MURR's Archaeometry Lab, we analyze for about 30 elements, generally at a sensitivity level of parts per million by weight. This means we can distinguish one microgram of an element among a gram of multiple elements, or at the level of one-millionth of the gram—and that is highly sensitive. [For some elements we take it to one part per billion!] We then pair two elements together to produce a graph. The possible pairings for 30 elements are nearly 900, but our scientists usually have a good idea which pairings will yield relevant information. It is the clusters of data points (concentrations of the two elements) on the graphs that we try to match—an obsidian artifact from a particular obsidian quarry will have the same level of concentration of those two elements. If we put the artifact graph on top of the source graph, the clusters would appear in the same place for each. The same holds true for matching the pottery sherd with its original clay soil source.
Other possible applications for NAA in archaeology include studies of prehistoric technology (i.e., determining how materials were made), studies of the uses of different artifacts, and studies to determine the authenticity of questionable artifacts.
The Archaeometry Lab at MURR supports faculty and student research efforts from several University of Missouri-Columbia (MU) departments, including Anthropology, Art History and Archaeology, Geography and Geological Sciences. But it is also a national, even international, resource. For well more than a decade the National Science Foundation (NSF) has provided significant funds to make MURR's Archaeometry Lab accessible to faculty and student researchers at educational institutions throughout the country. One aspect of the NSF program brings graduate students from other universities to MURR for a several month-long internship and invaluable hands-on experience. Usually they bring samples from archaeological digs to analyze for their thesis research. Under the mentoring of MURR faculty and staff, they learn how to prepare the samples for irradiation, perform the analytical techniques, evaluate the results, and then present their findings in a professional setting.
Archaeometry's Role in Understanding the Legacy of Human Culture
Archaeologists dig, pick and sift through archaeological sites and examine very carefully whatever material remains they find to gain an understanding of prehistoric human behavior. Artifacts such as stone tools and pottery remains from a prehistoric site—perhaps hundreds or even thousands of years old—are fascinating not only to archaeologists but to many others because these artifacts are often our only guide to recognizing the activities of early humans. Since there is no written history, the artifacts are scrutinized to glean whatever we can about the people who made and used them. Many times they are our only connection to those ancient peoples, and are among the few items that reflect their daily lives.
By employing various physical and chemical techniques to examine artifacts, archaeologists systematically can collect, evaluate and analyze data to try to imagine and visually recreate what life might have been like. Archaeologists call it modeling, testing, and theorizing the nature of past human activity. The application of physical and chemical techniques for archaeological study is commonly known as archaeometry.
A powerful archaeometric techniques is the method of neutron activation analysis (NAA), which uses thermal neutrons from a nuclear reactor to determine the chemical make-up of artifacts. When we put a small sample of the artifact in our reactor for a very brief time. The neutrons produced in the reactor "activate" the sample. That is, they make it radioactive. Every radioactive element gives off a specific radioactivity signature that can be read (detected) by special instruments. When activated, the artifact gives off a radioactive signature that corresponds to its chemical composition. In this way we learn about the chemical ingredients in the artifact—which elements there are and how much of each. A tabulation of this compositional data for an artifact is known as its chemical fingerprint.
What is "Sourcing"?
Sourcing involves matching the artifact with the original site, quarry or outcropping it came from by comparing chemical fingerprints. The artifacts most frequently studied by NAA at MURR are ceramics and volcanic obsidian. Pottery is one of the most common forms of artifacts found at archaeological sites, and obsidian fingerprints are highly unique. If we perform NAA on a piece of pottery, which is made of clay, we can compare its chemical fingerprint to those of other pottery pieces (or sherds) to see if they are from the same clay soil. If we can match the pottery sherd to the chemical fingerprint of a particular clay soil (the source), then we have found a link to its place of origin or manufacture. Many times the pottery sherd's chemical fingerprint does not match those of the local soils, which means that the piece did some traveling, perhaps with migrant peoples or because of trade or conquest. A diligent search for a matching clay soil may lead to "proof" that contact did occur between different groups of prehistoric peoples.
In the case of obsidian, researchers gather samples from the various quarries, bring or send them to MURR for NAA, and the data collected (the chemical fingerprints) from each of the sources go into a database. Then when someone sends us an artifact for analysis, we can match its individual fingerprint against the quarry fingerprints to determine which quarry is the source for the obsidian.
Research performed by the Archaeometry Laboratory at MURR after August 2014 is supported by the National Science Foundation under our current grant number 1415403. Earlier research was supported by several NSF grants including the following: 1110793, 8801707, 9102016, 9503035, 9802366, 9977237, 0102325, 0405042, 0504015, 0802757, 0922374, and 0802757. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.
Last Updated on May 14, 2015
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