Improvements In Radiocarbon And Archaeomagnetism Dating Techniques

Yale University, New Haven CT

Investigators

Abstract

Radiocarbon has been truly revolutionary in its contribution to our knowledge of world prehistory. However, over 60 years on, there are still weaknesses (irresolvable due to the basic physics of the method) that limit its effectiveness when applied to certain key periods in the human past. A newer dating method, archaeomagnetism, has proven its effectiveness in resolving two of these weaknesses. One is the large standard deviation (the +/- range of dates) that often extends longer than the beginning and end of the event one wishs to date, and the other is the periodic flattening, or plateau-ing, of the radiocarbon calibration curve (by which one derives calendar dates) such that nothing between 800 and 400 BCE (before the common era) can be dated more precisely than 400 years (the so-called "Hallstatt Plateau" cursed by prehistorians around the globe). The last millennium BCE is precisely when many innovations at the core of world history - beginnings of states and cities, emergence of crafts and metalworking to name just a few - had their explosive beginning and rapid evolutions. The Yale Archaeomagnetism Laboratory, opened in 2013, is dedicated to application of the method worldwide. The present project is integral to the next stage of the lab's development which will feature not only high-precision dating of archaeological materials, but also the development of methods to derive data from archaeological contexts on changes to the intensity of the Earth's magnetic field data critical to geophysicist's attempts to understand the fundamental mechanics behind the generation of the magnetic field. The Yale Archaeomagnetism lab was founded explicitly to address the worrying lag in the production of archaeological scientific data in America compared to the outpouring of those results coming from Europe (the so-called "Quiet Crisis" in American archaeology). The refinement of high-precision archaeomagntic dates and the generation of heretofore unique magnetic intensity data rely upon finding archaeological sites with deeply stratified deposits, with an abundance of burnt features (hearths, furnaces, fired houses), built of earth of the correct mineralogy so that those features record the Earth's magnetic signal at the time of burning. Along the Middle Senegal Valley in West Africa, at sites with evidence of Africa's earliest iron smelting (first millennium BCE) and of the continent's earliest "state" (Takrur, first millennium CE), the project team already has two decades of experience excavating features with exactly those characteristics. This two-year project will result not only in the generation of data to push the science forward, but also in the training of six Senegalese students and researchers in sample-taking (so the dating can continue beyond the two years of NSF funding). The newly refurbished radiocarbon laboratory at the University of Dakar, Senegal, will use radiocarbon samples taken at these sites in tandem with the archaeomagentic samples as a necessary part of its renewal, a process of returning it to service after nearly thirty years that has been delayed for lack of samples. Lastly, but not least, one simply cannot answer core questions about one of the most spectacularly innovative periods in the prehistory of Africa, taking place along the Middle Senegal during those two millennia, without dates of higher precision than conventional radiocarbon can provide.