Chronology is a fundamental part of archaeology. All of the questions we have about the past require an accurate knowledge of chronology in order to answer them satisfactorily. Establishing the timing and sequence of events is central to integrating the rich and diverse strands of material evidence available to archaeology. Scientific techniques have revolutionised chronological estimations for archaeologists, and are increasingly able to provide chronological resolution on the scale of single human generations, allowing the understanding of change on the level of a human lifespan.
In addition to refinements of established techniques (including greater precision, smaller sample sizes, less destructive techniques, and faster and more economical processing), new approaches are continually being developed. The range of different dating techniques available represents considerable research potential for archaeology in Scotland. In order to harness this potential, however, and to decide the best application of each technique, there is a need to understand the information that it can (and cannot) provide, as well as the approach (or combination of approaches) that should be utilised. The infrastructure and knowledge base for different dating techniques differs across Scotland with different expert practitioners, centres of excellence and facilities relevant to different aspects of chronology.
Relatively established techniques are briefly listed below.The most extensively utilised technique within Scottish archaeology – radiocarbon dating- can be used to date organic remains and inorganic carbon-containing materials such as shell. Luminescence dating can be used to date minerals such as quartz or feldspar within ceramics, lithics and sedimentary materials according to their last exposure to light or heat. Dendrochronology uses tree-rings to date wooden material according to when it lived or was felled, and long-term dendrochronological sequences are now being constructed for Scottish material. Tephrochronology is based on the identification and correlation of volcanic deposits. Cosmogenic nuclide dating has been widely utilised within earth and environmental sciences to date exposure of surfaces through analysis of radionuclides formed in surface rocks and soils (including 10Be, 26Al and 36Cl) and has now been developed to explore timescales relevant to archaeological analysis; cosmogenic nuclide analysis can also be used to determine ancient rates of erosion, an issue that is potentially useful in understanding human impact in the archaeological record. Amino acid racemisation dates marine molluscs and archaeomagnetic dating is used to date fired structures, such as hearths or kilns.
The selection of a particular technique will depend upon the circumstances of any given archaeological research. This requires consideration of the likely age and type of material available and the levels of precision and accuracy required, and should be reflected in suitable dating strategies. The limitations of each technique should be considered (bearing in mind that these may change depending on context), as well as the need for relating scientifically-derived information from specific samples to contextual information from the site, building, artefact or landscape.
Dating strategies should be fully considered at the start of a project and consistently re-evaluated as new evidence comes to light. This not only helps to ensure that a dating opportunity is not missed in the field, as optically stimulated luminescence and archaeomagnetic sampling must occur with in situ deposits, but it also encourages an on-going dialogue between the archaeologist and dating specialist that will only serve to increase the reliability of any dating undertaken. This is especially important since the statistical modelling and analysis of data, where applicable, should also form a component of further analysis. If the dating programme is developed and undertaken using a Bayesian framework, the results will be robust and a greater precision will almost certainly be achieved.
Building on established techniques – as well as developing both new approaches and novel applications of existing techniques – offers to archaeology an increasingly powerful set of tools. Archaeology in turn can provide a driver for developing and improving techniques. The relationship between the sciences and archaeology in terms of chronology is therefore mutually beneficial, and absolutely essential for answering questions about people in the past.