Staff spotlight: Dr Rachel Wood
What was your route into archaeology, and did you always intend to specialise in chronological dating or were you ever tempted by other topics/areas in the discipline?
At school I enjoyed (nearly!) every subject, and was always torn when asked what my favourite was. The answer was often history or geography, but chemistry and biology would appear almost as much. I loved hiking and being surrounded by both our human and environmental past, and was equally as happy looking at glacial features in the Lake District as exploring a castle on the South Coast, or separating the colours of felt-tip pen ink on a wet day. Choosing my A-levels was a challenge, and although I focused mainly on science, I always had in mind that I might be able to use this to study archaeology or geology in some of the ways that were starting to be shown on TV. I particularly remember a 2 minute snippet about lipids in ancient pots, and by the end of my A-levels I knew I wanted to do something combining archaeology and chemistry. So, I applied to study Archaeology and Chemistry within the Natural Science degree at the University of Durham followed by an MSc in Archaeological Science in the School of Archaeology, combined with lots of museum and fieldwork. I spent 6 months working at the Salisbury Museum, before returning to study for a DPhil with Tom Higham as a supervisor. I think I fell into chronology. I find all of the ways scientific methods and techniques can inform us about our past fascinating and love working on interdisciplinary projects to learn more!
What is the simplest way you have developed to quickly explain (to children or someone unfamiliar with our discipline) how radiocarbon dating works?
There are three types of carbon. The two most common types are stable, but radiocarbon is radioactive. This means that it ‘decays’ – it turns into nitrogen – at a known rate. It doesn’t matter what we do to the bone or charcoal, this rate of decay will stay the same. We can heat it up, and radiocarbon will keep on decaying at the same speed. This means it provides a really powerful way to work out how old things are over the last 50,000 years. Radiocarbon is produced high in the atmosphere when cosmic particles hit the atmosphere, before taken in by plants during photosynthesis as carbon dioxide and passed on through the food chain. By comparing the amount of radiocarbon remaining to the stable forms of carbon in an ancient sample, we can work out the last time something was alive. There is hardly any radiocarbon around (we don’t think of ourselves as particularly radioactive), but over the last 70 years several ways of measuring the tiny amounts remaining have been developed, and we are now able to count individual radiocarbon atoms.
What is something about radiocarbon dating that might surprise a lot of people?
The obvious thing is that it takes a long time, lots of people and loads of work to make a measurement! We are not CSI… More subtly, it might be that radiocarbon can be used to understand a huge amount about our world – both now and in the past. It is not just a dating method. It can be used to investigate how ocean circulation patterns have changed and whether rocks are releasing carbon dioxide because of climate change. We can even tell if someone has been eating fish! This is because although radiocarbon is produced in the atmosphere it can be taken into ‘reservoirs’ where it ages. For example, the radiocarbon in the tiny creatures that make up limestone has long since decayed. This means that if the rock degrades and releases carbon dioxide, we can easily distinguish it from carbon dioxide in the air using radiocarbon. It will also make aquatic plants and fish look really old if it is dissolved into a lake, and so we will look 100s of years radiocarbon-old if we eat enough of these foods.
What are some of the more memorable or unusual types of objects you get commissioned to radiocarbon date in the lab but which don’t necessarily grab the headlines?
Some fossilised fruitbat urine was a surprise! Julien Louys wanted to try, ‘just to see’ what he could learn about the past from a deposit from the back of a cave in Tropical South East Asia. It smelt like tropical fruit punch.
There are many others. Every sample has a fascinating story behind it, and we constantly feel privileged to work on a huge range of important sites and questions within ORAU.
What is the ‘bomb-pulse’ and why would it be of interest to vintage whiskey merchants?
During the 1950-60s, above ground nuclear tests nearly doubled the amount of radiocarbon in the atmosphere. Since the 1963 Partial Test Ban Treaty, the amount of radiocarbon compared to the stable carbon types in the atmosphere has quickly dropped. Not only is carbon dioxide dissolved into the ocean, but we are diluting it by burning fossil fuels. We are now at about the same levels as we were in 1950, and they are predicted to keep dropping unless we drastically cut carbon emissions. Whilst nuclear testing and the burning of fossil fuels are highly problematic, they do have a silver lining. The rapid change in the proportion of radiocarbon in the atmosphere, or bomb-pulse, means that we can use radiocarbon in the recent past to get very precise age estimates. The means radiocarbon dating can be really useful in forensic investigations – including in assessing whether a whiskey was produced in the same year as it’s label suggests.
How can radiocarbon dating help the plight of critically endangered animals?
By using bomb-pulse dating to estimate when an animal died, we can help to enforce restrictions on the trade in e.g. ivory or rhino horn, and to understand some of the temporal dynamics behind the illegal trade in wildlife. We can spot what proportion of carvings in a market were produced after bans on hunting, and can even identify where mammoth tusks were pulled from the permafrost and carved to produce forgeries (a problem in itself). Some of the most widely illegally traded animals such as pangolins, whose populations are collapsing in both South East Asia and Africa under the weight of poaching, are shy and elusive animals who have been little studied. Radiocarbon may help to tell us how long they live and their diet, potentially helping understand their ecology and so informing conservation measures – though this is still very much work in development.
What advice would you give to a current DPhil student who is about to defend their thesis in their viva?
Relax. You know more about your thesis than your examiners.
Your examiners are really interested in your work, otherwise they would not have agreed to examine it. This is a compliment and something to be proud of!
Your thesis might feel like your life, but it is just one part of you.
Tell us about a book you most recently recommended to someone else.
Death comes to Pemberley by P.D. James. The perfect wind down of almost Jane Austen, but far too easy. (Though after checking I had the correct author, I am now equally mortified/excited to find that it is a TV series as well!).
If you were a guest on Desert Island Discs, what luxury item would you take with you to the Island? (In accordance with the DI rules you can’t use it to escape or communicate).
After spending more than 10 years in Australia, I need to say a limitless supply of sun cream so I can explore during daylight hours without getting beaten down by the sun.
Which historical figure would you most like to meet?
I think I’d just like to walk down an early 19th century street or Palaeolithic trackway, and overhear the everyday conversations and watch the social interactions. Perhaps have a chat with Jane Austen on my way home to see if she would approve of Death comes to Pemberley!
