Hot Dates in Chi-Town

Archaeologists are notorious moochers. Or maybe I should be nice and just say we’re ‘highly adaptive’. Either way, we constantly pick up new techniques from other disciplines, such as using G.I.S. and performing DNA analysis on ancient skeletons. Even our trowels were designed for masonry work. So for this month’s blog carnival, I decided to pick a ‘classic’ article that was not written by archaeologists, but was written for archaeologists, and transformed our discipline. I give you a discussion of: James Arnold and (the more famous) Willard Libby’s 1949 article in Science ‘Age Determinations by Radiocarbon Content: Checks with Samples of Known Age’

Today, radiocarbon dating is a standard practice within archaeology. It is used to give chronological dates to organic remains from archaeological sites that are anywhere from a few hundred to about 50,000 years old. On the sites I’ve worked on, we usually try to find things like nutshells that are deep inside of pits or hearths and use those for dating, but any organic material will work. Radiocarbon dating has become so commonplace that detailed descriptions of the work are rarely discussed anymore, especially in popular literature, leaving the door wide open for critiques by young earth creationists who dispute its validity. However, at its inception, numerous articles discussing the technique and improving upon it were being published. Starting in 1947, publications about the idea of radiocarbon dating, and requests for samples from archaeologists were coming out. However, I think that the 1949 article in Science is the key work for archaeologists, because in it we saw the first clear, solid results showing that radiocarbon dating didn’t just have potential, it worked. While archaeologists already had dendrochronology (tree ring dating), this method has severe regional and temporal limitations. Most archaeological sites could only be given ‘relative dates’, meaning you could put the different sediment layers in order, and compare sites to one another as older and younger based on the artifacts you found, but you couldn’t give them any actual calendar dates. The ability to give statistically absolute dates to masses of archaeological sites revolutionized both our understanding of the past, and the purpose of the archaeologist him/herself.

Willard Libby in his lab in the 60s

In the 1949 article, Arnold and Libby gave a brief overview of the procedures they performed, including details about the size of the samples they were working with (8 grams of carbon! According to Beta Analytic, we can now get dates with as little as 0.00025 g of carbon). This kind of information was important, because archaeologists were wary of this new method. Archaeologists were trained to classify artifacts and identify soil horizons, but few knew much about chemistry and physics. The authors clearly explained the statistics used in their analysis and discussed procedures they used to check their equipment. They also explained flaws in the data (they improved the sensitivity of their equipment over time, reducing standard deviations around dates). They seemed to be trying to stop any grumblings from the peanut gallery before they started. The article then went on to describe the seven samples that Arnold & Libby dated, and the contexts in which they were found:

  • The ‘Centennial Stump’
  • A log from a cave in the southwestern United States
  • An Egyptian coffin
  • A Syro-Hittite period palace floor in Syria
  • A piece of an Egyptian funerary boat
  • A piece of cyprus from the Egyptian tomb of Sneferu
  • A piece of acacia from the Egyptian tomb of Zoser
  • I hadn’t realized how much of the early work was done on Egyptian materials, though it makes sense since the University of Chicago, where Libby worked, is home to the Oriental Institute, and since they were testing their methods by examining materials that could be dated by other means (tree rings or historical texts). Today we tend to use radiocarbon dating for prehistoric sites more than anything else. The last part of the article was a lot of name-throwing, and a request for samples. Since people were unsure about this new method, which they didn’t have the background to evaluate themselves, showing off all the archaeologists who were already supporting it was probably one of the best things this article did for increasing support within the discipline. Arnold and Libby, with the help of a guidance committee selected 11 foci for their future research, and found archaeologists who were willing to head up each question as follows:

  • Early Man – Frank H. H. Roberts Jr
  • California/Oregon – Robert Heiser
  • Hopewell/Adena (Midwest US) – James Griffin
  • The Mankato Glacier – Richard Foster Flint
  • Mesopotamia and Western Asia – Robert Braidwood
  • Peru – Junius Bird
  • Scandinavia and Western Europe – Hallam Movius
  • Southeast United States – William S. Webb
  • Yukon – Frederick Johnson
  • Valley of Mexico and Tepexpan Man – Helmut de Terra
  • Pollen Chronology – Edward Deevey
  • Looking back, these were extremely prominent men in the field of archaeology (save Deevey, who was a prominent paleolimnologist and Flint, who was a glacial geologist), and leaders of research in their given regions. Having all of them essentially sign-off on radiocarbon dating no doubt aided in the influx of samples and support by the discipline. By 1951, another article had come out in Science which had over 300 samples listed, and in 1952 the first edition of Libby’s book Radiocarbon Dating had been published. In 1960, he received the Nobel Prize in Chemisty for developing this technique. His Nobel Prize Lecture gives a nice overview of the history and process of radiocarbon dating for anyone who’s interested in learning more about it. There have also been numerous articles in American Antiquity that discuss the history of the development of radiocarbon dating as well. Radiocarbon dating had profound implications for archaeology. For decades archaeologists had been spending much of their time trying to develop relative chronologies of archaeological sites, by comparing the materials found at each one. Massive amounts of thought and time went into developing organizational methods for dealing with these materials. And suddenly, it was possible to take just a few carbonized objects at a site and get a date for that site. Or take samples from different layers of a site and see how long the place was inhabited, and if there were any gaps in the habitation record. You could quickly have a chronology for your region. And what timing! The United States started work on the River Basin Surveys in 1946. The Works Progress Administration (WPA) had decided to dam up several rivers as part of their public works programs, and this was going to bury thousands of archaeological sites under water. So the River Basin Surveys were set up to document as many of these sites as possible. Undergraduate anthropology majors were sent off with huge crews of untrained men to excavate as many of these sites as they could before the waters began to rise. Officially, the River Basin Surveys went on through 1969, but I’ve heard rumor that the Smithsonian is still cataloging artifacts from it. And while I don’t have numbers on how often it was used, I suspect that the development of radicarbon dating was extremely helpful to the archaeologists in charge of organizing all of this material. In the years following the development of radiocarbon dating, archaeology was transformed. Archaeologists now had the ability to focus more of their time on larger anthropological questions. Questions about social organization, settlement patterns, the rise of civilizations – all of these questions had been studied in the past, but radiocarbon dating made it easier to focus on them. At the same time, new sub-disciplines were developing – zooarchaeology, paleoethnobotany, etc… with less time needed to develop artifact seriations, more time could be spent examining materials that could not be seriated, and thus more detailed examinations of what it means to be human could be examined. Archaeology was become both more scientific and more concerned with greater anthropological questions. Radiocarbon dating was just a part, but an extremely significant, if not essential part, of the development of this new era in archaeology.

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