Each year, three Penn undergraduates take on a venerable task: curating their own exhibition at the Penn Museum. This year’s student-run show, Key Questions: Unlocking Florida’s Ancient Past, focuses on a well-preserved archaeological assemblage from the site of Key Marco, Florida. It explores the fascinating discoveries and identifies the mysteries that are still unsolved, pointing out how archaeological science can help us find answers. This is the ninth year of the student curatorial program, but it’s the first time our curators have conducted new scientific analysis on objects included in their show. Samples from four objects were sent for carbon-14 dating, and the results revealed important new information about the residents of Key Marco and the remarkable objects they made. The evidence has expanded our understanding of the site by helping us determine which culture made and used these objects.
The site was excavated in 1896 by Frank Hamilton Cushing. As one of the first archaeologists to use a grid system, Cushing’s excavation methods were innovative for the time. Thanks to the waterlogged environment of Key Marco, materials such as wood and fiber were preserved— fragile materials that that rarely survived elsewhere in the American South. Cushing and his crew did not record stratigraphy, complicating our ability to date the objects. A lack of European material indicates the site predates Western contact, but there is debate about whether the objects were deposited before or after 1350 CE.
Previous radiocarbon dating attempts provided inconsistent results. In 1968, a piece of cord was dated to 1670 CE. Six more results from 1975 varied wildly: from 30 CE to 850 CE. These dates have been contested due to possible contamination from pesticides and other early conservation techniques. We hoped that dating four of the objects from our Key Questions show would allow us to definitively assign them to either Glades or Calusa culture, which would contribute to the scholarly conversation around Key Marco and lay the groundwork for future research.
We examined the objects under ultraviolet radiation to rule out any that might have been contaminated, which could jeopardize the dating process. Conservation materials such as glues, varnishes, and plastic resins appear fluorescent when exposed to UV radiation, which allowed us to omit treated objects—such as the pestle fragment—from our list.
Radiocarbon dating is, by definition, a destructive method. We submitted a proposal to the Penn Museum’s Scientific Testing Committee, and to minimize harm to the collection, we chose objects that were associated with small fragments that could not be reattached, or that had residue we could scrape off without harming the object. Four objects were approved for testing: a panther jaw (40703), a piece of netting (40548), a large vessel (40184), and ceramic fragments (40265). These objects cover a wide range of organic materials—bone, fiber, wood, charcoal— which minimized biases that could result from tests on a single material type. Samples were collected in the conservation laboratory and sent to Beta Analytic for testing.
Museum Object Number(s): 40225
The results were remarkably consistent. The panther jaw, netting, and large vessel dated between 1260 and 1293 CE, while the ceramic residue dated approximately 100 years earlier, suggesting that it may have been deposited before the other three objects. The dates all sit comfortably within the late Glades time period. This consistency increases our confidence in the resulting date range, which means that this information can be used to help understand other objects from the site. Still, despite this confidence, our exhibition only attributes these new dates to the four objects we tested, leaving the other objects in the exhibition with a broader date range on their labels, from 500–1500 CE. (We will wait for regional specialists to weigh in for more specific dating.) Meanwhile, we plan to publish our newly tested dates in a scholarly journal soon, and we hope that they can open the door to further analysis, especially since radiocarbon dating is more accurate and accessible than ever. With additional dates, we could determine early and late boundaries for the site’s occupation, reconstruct a sequential timeline for the excavated materials, and build a clearer picture of which people left these objects behind. Dating a site is much more than an abstract number: understanding the age of the site allows us to use Key Marco to better understand other southeastern sites, and if we know certain sites existed at the same time, the artifacts from Key Marco could hint at a much bigger story than the site itself. They could help answer questions about the organic material culture that is missing from the archaeological record of other pre-contact native groups.
Megan C. Kassabaum, Ph.D., is Weingarten Associate Curator of the American Section and Associate Professor of Anthropology. Sarah Linn, Ph.D., is Associate Director of Academic Engagement. Anna Hoppel is a senior in the PAFA/Penn B.F.A. program, majoring in Fine Arts with a minor in Art History. Sydney Kahn is a junior majoring in Anthropology with a minor in Creative Writing. Qi Liu is a junior double majoring in Anthropology and Art History.