Chronology provides a fundamental structure for our understanding of the past. Timing reveals the sequence of past events and the tempo of change, and provides a window on human temporality. Scientific dating enables us to provide increasingly refined chronological frameworks for the historic environment, enhancing understanding and appreciation of its value and significance, informing conservation and protection, and enthusing the public about their heritage.
Constructing robust chronologies requires rigour at all stages of the dating programme. Bayesian statistics provide an explicit methodology for combining different strands of information to provide such a chronology. They have proven particularly valuable in handling the complex probability distributions of calibrated radiocarbon dates, but it is also possible to include dates from coins, historical sources, dendrochronology and the results of other scientific dating methods such as luminescence and archaeomagnetic dating. A scientific dating programme undertaken within a Bayesian framework should thus be the norm, not the exception.
Radiocarbon dating is applicable to an extensive range of materials that commonly survive in archaeological sites, historic buildings and palaeoenvironmental records. It can be used for samples up to about 50,000 years old. It is widely available on a commercial basis, and measurement error compares favourably with many other techniques. It is thus the scientific dating technique most commonly used to understand heritage assets, although its complexities raise formidable challenges in constructing robust and precise chronologies.
This guidance is designed to lead the reader through the Bayesian process that should be at the heart of all scientific dating programmes. It aims to provide the non-specialist reader with the necessary information to employ radiocarbon dating appropriately, and to be aware of the scientific and statistical complexities that can arise and require specialist support.
This document is intended for:
- curators who advise local planning authorities and issue briefs;
- project managers writing specifications or written schemes of investigation;
- those working on development-led or research projects (in particular post-excavation project managers);
- other practitioners.
These guidelines are designed to be relevant to archaeological projects funded under the planning process within England. They concentrate on using radiocarbon dating and chronological modelling within the Holocene Period. Specialist advice should be sought when dating earlier sites (guidance on dating techniques for the Pleistocene Period is currently in preparation).
Although the general principles of these guidelines are widely applicable, there are some technical aspects of radiocarbon dating that are not covered in this document, as they are not usually relevant for English sites. Such issues include, for example, the dating of marine shell. Very little information will also be found on materials that are dated only rarely (for example, chitin), and again specialist advice should be sought before submitting such materials for dating.
An introduction to the methods is provided in section 1 and section 2, covering radiocarbon dating and Bayesian Chronological Modelling. A step-by-step guide to the practice of implementing a radiocarbon dating programme is provided in section 3 (and summarised in Fig. 11), including a series of flow-diagrams to aid readers through various stages of the process (Figs 18–21, 23 and 25). Project management within the English planning framework is discussed in section 4 and a range of case studies is provided in section 5. A glossary is provided for less familiar terms, and an appendix details sources of further advice, information and resources.