Radiocarbon dating Ireland database

Guest Blog: Robert M Chapple – Irish Radiocarbon Date Open Data

Who is this dude?

RobertChappleFor many people, going from being a field archaeologist, digging up sites across Northern Ireland, to working in data analytics seems like a big jump. In some respects that’s true – there’s a big difference in where I go to work and the way I collect data, but there are many commonalities too. While archaeology may appear to be about finding cool stuff from the past, at its core it’s really about gathering data. Data on past lives, social organisation, diet, health, funerary practice … it’s all archaeology … and it’s all data!

For all that, these days I describe myself as a ‘recovering archaeologist’. After more than 20 years in the commercial sector, I made the difficult decision to leave the profession in 2011. I was lucky enough get the opportunity to retrain with a large IT company in Belfast. My IT day job mostly concerns producing data visualisations for a range of clients within the organisation, but I still maintain a number of personal research interests within the archaeological world.

What if???

One night back in 2006, I was sitting at home, writing up a final report on the excavation of a type of site known as a ‘burnt mound’ or ‘Fulcaht fiadh’. At these sites, stones were first heated in a fire and then plunged into a trough of water. The process brought the water to the boil and resulted in lots of heat-shattered rock. Although a number of hypotheses have been advanced over the years (including their use in making beer or for dyeing) they are conventionally thought to have been used as cooking places and their core period of use appears to have been in the Bronze Age (c. 2350/2200-650 BC).

The usual research pattern for writing up a site of this type often includes comparing its morphology with other similar sites, either on the same excavation, in the same county, or seek parallels with well-known published examples from elsewhere in Ireland. This is a perfectly valid approach and one that I’ve frequently used. On this particular night my mind was drawn to another burnt mound site that I knew I’d soon have to write up. The radiocarbon dates I’d received for this second site indicated that, although separated by a large physical distance, they would have been relatively close in time – nearly contemporary, in fact. However, one site was characterised by a single, deep, sub-rectangular trough, while the other had a pair of shallow, circular troughs. It really struck me that the research methodology outlined above would never bring these two sites together, no matter how close in time they were.

This was my ‘What If’ moment … I wondered ‘what if we had a single, searchable repository of radiocarbon dates where we could compare radiocarbon dates from similar sites?’ … or even dissimilar sites that were actually contemporary … It might be just as interesting and rewarding as comparing morphology.

What is a Radiocarbon date?

For anyone not familiar with archaeology, it may be of benefit to break away for a moment and explain what a radiocarbon dating actually is. At the simplest level, it’s a laboratory method that uses the predictable decay (half-life) of the naturally occurring radioisotope carbon-14 (14C) to determine the age of carbon-bearing materials. Carbon is found on archaeological excavations in a number of forms, including wood (remains of hearths or burnt buildings) or charred cereals (remains of, say, a burnt out cereal drying kiln).

The amount of surviving 14C is measured and this is used to determine how old the item is. This can then be used to determine the age and phasing of activity at the archaeological site. The date comes back from the lab in the form of XXXX±XX BP (Radiocarbon Years Before Present), and this calibrated to produce a calendar date. For example, a date of 2456±22 BP would calibrate to the period from 753-416 cal BC.

The date can also have significant metadata associated with it that will be of value to certain researchers, including excavation context, the exact type of material dated, lab processes etc. It’s pretty complex, but those are the basics.


Robert’s Library

The Irish Radiocarbon & Dendrochronological Dates Project

Unfortunately, my wonderful ‘What If’ was beset with troubles. The biggest one was the dates themselves. They are scattered across a vast array of books, journals and ‘grey literature’ reports. Even where they are available, they can be difficult to access – academic books are frequently produced in relatively small print-runs, some journals may only be found in specialised research libraries, or behind pay walls.

The ‘grey literature’ reports may exist in only one or two physical copies, otherwise residing on an archaeological consultancies’ hard drive. No matter how you look at it, bringing this data together would not be an easy task. My simple solution was to start with my own library and go from there. I’ve been collecting books on all aspects of Irish archaeology since I was an undergraduate and, while not without lacunae, it’s pretty good. Because you just can’t beat a snappy title, I called it The Irish Radiocarbon & Dendrochronological Dates Project (IR&DD). The most recent version of the resource holds data on 8,288 radiocarbon determinations and a further 313 dendrochronological (tree ring) dates.

Next Steps

For all that, something had been bugging me for a while. Radiocarbon dates are a rather specialised form of data that even professional archaeologists can find difficult to use. However, the dates themselves relate to real life events in the physical landscape. The specialised nature of archaeological literature means that it often fails to effectively connect with interested non-specialists in local communities. The difficulties in working with radiocarbon dates are such that this further, seemingly arcane, specialism obscures this important data to all but a small number of professionals. My question was ‘How do I reach these people?’

My thought was to turn to Tableau, the tool I use daily in my IT career. The enterprise data visualisation package has a slightly-limited version (Tableau Public) that is free to anyone to download and use. That is why I spent much of my free time over the summer of 2015 manually adding geolocations to every Irish radiocarbon date. By autumn of that year I was able to spend time with Tableau creating and editing my visualisations.

At that point my process timeline was this:

  • 10 years of manual data gathering
  • three months of geocoding
  • one week of Tableau visualisations

The result has been an evolving collection of dashboards that allow both professional archaeologists and non-specialists the opportunity to see and interact with this data in new and meaningful ways.

Click to view on Tableau

At the time of writing, the front page of the dashboards shows a map of the island of Ireland with every date represented as a single dot. Here the user can select the county or counties that interest them most and/or the broad archaeological time periods of relevance to them. This can be at the very broad level of Neolithic, Bronze Age, and Iron Age, or somewhat more granular where the Neolithic, for example, is split into its Early, Middle, and Late phases.

Tableau also includes a suite of tools to select rectangular, circular, or irregular areas for more detailed study. On machines with geolocations enabled, it allows the user to centre the map on their own location and see the dated archaeological sites and artefacts in their own areas. The second tab is designed for the more specialised researcher (or perhaps one that doesn’t agree with my approach to phasing the past). Here the user is again able to select single of multiple counties, but there is a wider range of temporal controls available. Four sets of sliders give various forms of control over the selection of time period, from the uncalibrated age BP; the calibrated modal date BC/AD; the calibrated intercept date BC/AD; and the calibrated intercept date BP. This should give even the most sophisticated user the power to narrow down the dataset to just what they’re after. The final tab is a dynamically-filtered reading list, giving reference to published works and a selection of the associated metadata for each date.

From the feedback I’ve received, it is clear that the Tableau dashboards have been an aid to professionals and university students interested in both landscape and temporal research, allowing them to quickly and easily select the subset of the data that is most relevant to them. The feedback I’ve received from a number of non-specialists is that this project allows them easy (but not ‘dumbed-down’) access to local-level information that they would not normally be able to find. In so doing, it is starting to bring an appreciation of deep-time archaeology to parish-level research. For myself, I hope that this resource – both the dashboards and the underlying dataset – will continue to spur interest and engagement with our ancient past.

What’s it really worth?

Depending on the laboratory you use to produce a radiocarbon date, along with other factors, such as the speed at which you need the results and the exact type of process used, you can spend between US$390 and US$595 per date. Taking an average of US$490, this would indicate that the IR&DD resource represents data worth US$4,061,120 … or about £2,929,044.

Without doubt, that’s a significant chunk of money, but (for archaeologists, at least) the real value lies in the data and what it can tell us. Unlike estimating the cash price of creating a radiocarbon date, the knowledge value here isn’t additive, it’s multiplicative. What I mean by this is that one date is just one date – it dates one thing: the pit, ditch, or post-hole it came from. Many dates from a single site (or from a range of similar sites) can allow us to create detailed chronologies either of the phasing of that individual site or the evolution and development of the site type as a whole. In this way, the knowledge gained is worth more than the sum of its parts. This is the opportunity that the IR&DD resource offers – all of the dates together could reshape our understanding of Irish archaeology.

Radiocarbon Landscapes

In my own work, I’ve attempted to pioneer the use of what I term ‘Radiocarbon Landscapes’ where connections are made between contemporary events across the island that would not be drawn together by traditional research pathways that concentrate on morphology alone. For example, this approach to the study of burnt mounds pulls together other burnt mounds, but also contemporary settlement sites and burials etc. While I don’t claim that it is a research ‘silver bullet’ to obviate all other methodologies, I do believe that it is a more holistic approach to archaeological research.

Set your data free

Set your data free

Whatever use I put this data to, I am mindful of the collaborative nature of this project, relying on the interest and good will of so many others. For this reason, I’ve taken the position that I act as curator, rather than owner of this data. Although this dataset was originally created as a personal research resource, I’ve always been keen to share it freely with any interested scholar. Initially, this was simply via email, but since 2010 it has been available to download. I offer the resource without fees, restrictions, or copyright claims of my own.

I have also taken the decision to keep the data in a ‘vanilla’ Excel spreadsheet. My reasoning for using Excel is that it offers the greatest accessibility and flexibility to other users who can either work with it in that format, or easily import it to more specialised applications.

To date, the IR&DD resource has been used by a wide range of archaeological researchers. These include a number of Irish National Strategic Archaeological Research (INSTAR) projects, including the ‘People of Prehistoric Ireland: Health and Demography’ project; Prof. Stephen Shennan’s ‘Prehistoric Demography’ project at UCL; it is a core document in two undergraduate courses on archaeological data analysis; and has been used by more undergraduates, MAs, PhDs, and post-Docs than I can easily count.

I think you can guess that I’m very proud of this achievement. While I take pride in the fact that other people are able to use my work to gain new insights and understandings, I’m more proud of the idea of what’s achievable by putting available data together in one place and making that freely available – for me those are the real achievements.

Where to next?

My first instinct is to adhere to Bob Dylan’s advice in Tangled Up in Blue and ‘Keep On Keepin’ On’. Archaeological sites continue to be excavated, dated, and published and while that endures there will be a need to keep the dataset as up to date as possible. The dashboards will, I hope, continue to evolve as I develop the technical skills to create further visualisations and refine those already available. However, the biggest and most important step forward for the profession must be the normalisation of the concept of open data generally (and 14C data specifically). Much progress in this direction has been made in recent years, but it will only continue if we can demonstrate its value to all stakeholders – both professional and non-specialist.

This is a guest blog post from Robert M Chappel, an ODI Belfast supporter.
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