Over the last few weeks, we’ve been talking about the cremated human bones uncovered on DigVentures’ crowdfunded excavation. About 4,000 years ago, these cremated remains were gathered up and placed inside an urn, along with a stone tool and a piece of pottery.
When we published a post about the bones we found inside, lots of people on Facebook and Twitter asked us whether we would be able to analyse the DNA from this individual, and compare it to living populations. It’s a great question, and one that is entirely understandable; after all, most of us want to feel connected with the past of where we live, or are from in some way. In fact, one of the things that got me interested in archaeology and osteoarchaeology and connecting with the past was Meet The Ancestors – a BBC documentary series about the excavation and scientific analysis of archaeological human remains.
In answer to the question, we’ve got some bad news, some good news and some really good news. To explain, we first need to understand what happens when a body is cremated and how this alters the bones.
In Britain, cremation was common from the Early Bronze Age right through to Anglo-Saxon times. There are also examples of cremations in the Mesolithic and Neolithic. To carry out the cremation, the mourners would have built a wooden pyre and from experimental studies, we know similar pyres reach temperatures of 600°C and above.
Bone is made up of around 14% water, 24% organic matrix and the remaining 62% is bone mineral. During cremation, bone loses large amounts of water and organic contents. At around 400°C the loss of these components is significant, and by 700°C it’s nearly all gone.
Looking at the colour of the bones from this cremation, we can say they were cremated at around 600°C or more. Since DNA is an organic component of bone, this means most of it will have been lost or destroyed from the heat of the pyre. Additionally, DNA breaks down over time, and this process is hugely influenced by the preservation conditions. So you can see why extracting even a tiny bit of DNA from a 4,000 year old cremation is not possible.
While archaeologists don’t yet have the tools to recover ancient DNA from cremated remains, forensic techniques are improving all the time. For now though, we’re limited to retrieving and analyzing DNA from well preserved remains that haven’t been cremated.
This isn’t all negative as researchers are always developing new techniques that enable us to find out more about the past. One fairly recent development in archaeological science is that we are now able to do isotope analysis on cremated bone to see where someone lived.
Isotope analysis is a technique that allows us to look at where a person came from, among other things. During life, the chemical elements that people absorb into their tissues have different isotopic ratios depending on their diet and water supply. These ratios differ depending on the geology and location, this can in turn tell us where a person came from.
Read more: Interview with a Forensic Archaeologist
Archaeologists have been able to do isotopic analysis on un-cremated bone for years, and on a whole range of elements including, carbon, nitrogen, strontium and oxygen. It is only recently that archaeological scientists have been able to do this with cremated bone and strontium.
However, this isn’t possible with any piece of bone. This is only possible with a very specific part of the skull known as the petrous portion, the inner part of your ear bone. As this part of the skeleton is formed before birth, this tells us the strontium ratio at this time.
Among the almost 3 kilos of cremated human bone we excavated from the Morecambe urn, we did find a petrous bone! In summary, that means we will be looking to conduct strontium isotope analysis on the cremated bone from the Barrowed Time project, which should tell us whether this individual was from the North West, or came from somewhere else.
We will also be looking to get radiocarbon dates from the bone, which will add to our overall timeline of the site and where it fits in the chronology of Britain’s Early Bronze Age.
A big thank you to everyone who got in touch to ask. In the meantime, if you’re interested in finding out more about ancient DNA and isotope analyses, have a look at this Heritage England guide.
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