Dating of Garbage Deposition

Significance

Why date garbage? The answer lies deep in the history of scientific thought and the study of the past. In late-18th-century Western Europe, scientists were looking for ways to understand the origins of geological deposits, challenging the assumed recent origin of the planet. While their efforts ultimately led to the recognition of the Earth's antiquity, they also cleared the way for an empirical study of the past. As field research intensified in the 19th century, the discovery of ancient stone tools alongside the remains of extinct animals showed the utility of stratified deposits to date ancient artifacts. More importantly, it became apparent that the bulk of past cultural remains is composed of refuse—objects and other remains that have been produced or modified by humans but which have lost their usefulness, becoming garbage.

Methods

The discard of trash and its accumulation are different than geological depositions. Consequently, garbologists (archaeologists who specialize in the study of rubbish and refuse deposits) have developed methods to order, sequence, and date trash deposits, from fresh rubbish to ancient archaeological contexts. Broadly, garbologists rely on two categories of dating strategies.

First, patterns of accumulation and superimposition of buried deposits can serve to create relative sequences of events. These patterns can bring insights into the conditions and the time elapsed throughout periods of trash deposition. The number of distinct strata as a proxy to the number of discard events, coupled with the thickness and compaction of the deposits, can all point toward frequency, intensity, and length of the use of middens (heaps of rubbish that represent the accumulation of daily refuse). Meanwhile, comparisons of changes through time can shed light on historical events and broader social changes. More broadly, stratified middens can be organized into broad periods by looking at the characteristics of broken artifacts and their change over time.

Second, the analysis of the physical and chemical properties of garbage deposits can provide chronometric and absolute dates. Chronometric measurements from stratified deposits give archaeologists the opportunity to place sequences of deposition in an absolute time frame. The most commonly used chronometric techniques for dating ancient garbage are radiocarbon and, more recently, accelerator mass spectometry (AMS). Radiocarbon methods measure the decay of a radioactive isotope (C-14) to evaluate the time elapsed since the death of a living organism. These techniques can be advantageously applied to many types of rubbish, including animal bones, charcoal, plant remains, shells, and paper. Precautions are needed when interpreting radiocarbon results, including archaeological associations to contamination, accuracy, and precision. Nevertheless, coupled with relative sequencing, chronometric dating is a powerful tool to date middens and their formation.

Challenges

The challenges of interpreting the chronology of garbage deposition are manifold. At the most basic level, a distinction has to be made between primary and secondary refuse. Primary discard typically happens at the place where trash is produced, whereas secondary depositions imply a certain delay in discard, such as the storage or transportation of trash away from the original activity area. The context of a hearth located in the vicinity of a habitation area where there is evidence for food processing and consumption provides a viable example. In this case, the discovery and radiocarbon dating of burned organic trash can provide a range of absolute dates for activities associated with that same household. Here, it can be assumed that the dating of a garbage deposition is somehow representative of the time when that trash was produced and discarded. In opposition, in the context of secondary trash deposits such as construction and landfills, garbage [Page 173]may have been accumulated and stored for an unknown amount of time before it was discarded. In this particular instance, absolute chronometric measurements provide a range of dates associated with the production of waste, rather than its discard. Moreover, secondary deposits might possibly contain remains from various places and primary activity areas, leaving the chronological interpretation of mixed trash uncertain.

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