Glossary

Absolute dating A form of archaeological dating that provides interval or ratio scale measurements, with the latter capable of being linked to a calendrical system.

Accuracy The degree of closeness of the sample measurement to the actual phenomenon of interest, an event in archaeological dating.

Measurement error The error formed by limitations in sample size, instrument precision, and calculation parsimony.

Precision The magnitude of measurement error.

Relative dating A form of archaeological dating that provides ordinal scale measurements, supplying older than/younger than age assessments.

Sample event The event for which a date has been obtained.

Stratigraphic superposition A geological law of sedimentary deposition stating that older layers are formed below younger layers.

Stratigraphy The documentation of a sequence of depositional layers, sometimes used as a shorthand term for stratigraphic superposition.

Systematic error An error that forms a bias of constant magnitude and direction in a particular methodology or research design.

Target event The event of archaeological interest for which an age is sought.

Determining when events of archaeological interest occurred remains a central and fundamental task for archaeologists around the world. Using dating methods to assess the age and duration of historically unique events is crucial in archaeology, as it is in other history-dependent sciences (e. g., geology), since chronology is essential for description, comparison, and analysis. Frequently, the larger goal in archaeology is to develop chronological sequences, where investigators aim to establish the temporal order of events to document (and through the use of theory, ultimately explain) change in the archaeological record. Thus, many archaeologists are continuously engaged in developing and applying new dating methods, as well as refining existing ones, as part of an ongoing effort to produce improved chronologies.

Establishing chronology in archaeology, however, is not as straightforward as it might first appear. First, what is actually dated is not an artifact, site, or culture per se, but an event of potential archaeological interest. It is important to distinguish between the ‘sample event’ (the event actually dated) and the ‘target event’ (the event of interest for which an age is being sought). Unfortunately, sample events are only rarely synonymous with archaeological target events because most dating methods employed by archaeologists have been developed outside the discipline in pursuit of other objectives. Some dating methods are able to produce age estimates for events that largely coincide with, or are identical to archaeological interests, such as establishing the time of last exposure to fire, the time of manufacture, or the time of artifact deposition. More often, however, bridging arguments are required to link the sample event to the archaeological target event. Such bridging arguments are often missing or not well developed in archaeology, negatively affecting the precision and accuracy of archaeological chronologies.

Second, all dates inherently contain some error, and these errors vary by kind, magnitude, and probability across the range of archaeological dating methods available. Some kinds of error, such as ‘measurement error’, result from the limitations of sample size, the complexity of calculations, and the precision of the instruments used to estimate a date. Other kinds of error, such as ‘systematic error’, constitute an inherent bias of constant magnitude and direction in a particular dating methodology or research design, consistently overestimating or underestimating the age of an archaeological event.

Lastly, the various dating methods used in archaeology have different methodological strengths and weaknesses; some methods offer high ‘precision’ (small instrument or measurement error) while other methods confer a high degree of ‘accuracy’ (the degree closeness of a measured date to the actual age). Although a few dating methods, such as radiocarbon dating, now possess both high intrinsic accuracy and precision methodologically, these advantages do not necessarily confer accurate and precise archaeological chronologies because the event dated is often not closely linked to the archaeological event of interest. For instance, the age of a manufactured wooden house beam and its use in construction may be of archaeological interest, but a radiocarbon date obtained from analyzing a sample of the beam may not necessarily record the time of these events. The radiocarbon method dates the time living entities stopped exchanging carbon with the biosphere (death). Except for the tree’s outermost ring which contained living cells just before death, all radiocarbon samples of the beam will record an age older than the death of the tree (systematic error) because the cells of the inner rings ceased exchanging carbon up to hundreds of years before. The use of old wood in construction and artifact manufacture complicates matters even further - it cannot simply be assumed that the time of the tree’s death corresponds to the events of archaeological interest.

It is important to consider the factors discussed above in evaluating the application of various dating methods to archaeological problems and contexts. A brief review of the history of archaeological dating is followed by a discussion of the various dating techniques used in archaeology.