Dating Ava: The radiocarbon dates

What is radiocarbon dating?

Over the next few weeks I’m going to be writing brief overviews of the different pieces of research we have undertaken during the project. I’m going to kick this off with the radiocarbon dates. For anyone who is unfamiliar with what radiocarbon dating is, I highly recommend checking out this page by the Oxford Radiocarbon Dating Unit, for an excellent introduction. I’d also highly recommend this article from The Conversation and this, the main C14 dating website, which has copious amounts of information.

Some summarising highlights:

  • Radiocarbon dating can be used to date most organic material from a couple of hundred years ago right back to around 50,000 years ago when humans first entered Europe.
  • The sample has to come from what was once a living creature (i.e. a plant, animal, or human) – things like metal or stone cannot be dated this way.
  • The results tell us when the living creature was alive, not necessarily when an object was made. For instance, a worked piece of animal bone will give a date for when the animal was alive, but it might have been years later it was crafted.

What did you sample and how many samples did you take for this project?

Over the years this burial has been radiocarbon dated three times. The first time was in the early 1990’s, but technology has developed drastically since then. We can now get much more accurate dates using the advances in technology. The other two samples have been taken in the last few months as a part of this research project. They include:

  • A sample of human bone from the lower right leg (tibia)
  • A sample of animal bone from the cattle shoulder bone (scapula)

Who did the radiocarbon dating for this project?

The radiocarbon dating of both the right tibia and the cattle scapula was undertaken by SUERC (the Scottish Universities Environmental Research Centre) at their Radiocarbon Laboratory in East Kilbride. It takes about 8-10 weeks for turnaround on the standard rate, but it’s well worth the wait! Each sample costs £315 (plus VAT).

Who funded the radiocarbon dating?

The first sample – the human bone – was funded by the Natural History Museum in London who are including Ava in an ancient DNA analysis project (see update in this project here). The second sample was funded by the Society of Antiquaries of Scotland who have been the major financial facilitator of this project since it started.

What are the new dates and what do they mean?

The way dates are presented – and what they mean – can be confusing, and I personally am still trying to get my head around what they mean. You are presented with an un-calibrated and a calibrated date which has been compared to a calibration curve (for more on calibration, see here, and for the calibration curve, see here). The calibrated dates (the best estimated range) are also presented on a scale of probability. Generally, a wider date range will have a higher probability, and a narrow date range will have a lower probability.

The two dates are very similar, which helps give us more confidence in the date range for when Ava died and when she was buried.

Sample Radiocarbon Age BP 68.2% probability 95.4% probability
Right Tibia 3827 ±33 2337-2204 cal BC 2456-2148 cal BC
Cattle scapula 3829 ±32 2337-2205 cal BC 2456-2151 cal BC

What do the dates tell us about Ava?

The original carbon dates (by Ambers et al, 1992) came back as 3700 ±50 BP, or as 2275-1945 cal BC at 95.4% (using Ox Cal v.4.3).  This means that Ava is now known to be around 200 years older than we had previously thought. This significant difference is due to the newer, more advanced technology and techniques currently being employed. The two new samples are also more reliable as they are very similar to each other, reinforced by the fact that the samples were taken, not just from different bones, but from different subjects.

The new dates tell us that it is very likely that somewhere between 4480 years ago and 4170 (give or take a year), was when Ava died. It also tells us that within this range it is most likely she died between 4350 years ago and 4220 (give or take a year).

 

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