Radiocarbon dating of macrofossil seeds

Project will identify new techniques for decontaminating samples

Dr Becky Briant of Birkbeck’s Department of Geography, Environment and Development Studies, has been awarded a facilities grant by the Natural Environment Research Council to enable her and a team of collaborators from the Oxford Radiocarbon Accelerator Unit, Royal Holloway and within Birkbeck to trial techniques that would enable accurate radiocarbon dating on macrofossil seeds from 25,000 to 50,000 years ago.

Radio carbon dating is a method used by geologists and archaeologists to determine how old organic material is, based on the level of radioactive carbon that remains in the material. It can be used to accurately date materials such as plants, seeds, shells and bones back to 25,000 years ago. Material between 25,000 and 50,000 years old is harder to date because by this time the level of radioactive carbon remaining within the material is low and it is easy to contaminate samples.

Dr Briant explains why being able to accurately date seeds from before the 25,000 year limit is important: “The period about 30,000 to 40,000 years ago was very important archaeologically – it was when Neanderthals were being replaced by modern humans within Europe. Environmentally, it was also a very important period – we have records from the Greenland ice core showing temperature fluctuations, and from the North Atlantic showing that we had really unstable climates with cyclical large fluctuations in temperature over 500-1500 years. Accurately dating seeds from that period will enable us to really understand the environmental background in which modern humans were developing.”

Dr Briant’s project aims to identify pretreatment techniques that successfully remove contamination from seeds from that period and make the dates more reliable. She has been working closely with specialist Dr Fiona Brock at the Oxford Radiocarbon Accelerator Unit to develop the most effective methods to do this.

Dr Briant explains why the site at Whittlesey, near Peterborough, where the seeds have been sourced from, was chosen: “The site is interesting because there have been several phases of river activity at the same site. There are deposits from the last glacial period – 10,000 to 110,000 years ago, which contain more than one channel with organic material, all of which are still exposed. Only 50 metres further away there’s an old river channel with material from the last interglacial – 125,000 years ago, and around the corner, two separate channels, which seem to date from different parts of the interglacial before that. It’s exciting as normally you would expect a set of river deposits to have only one of these climate cycles preserved in it. What’s more, the site provides large quantities of organic material. This is important, as many of the processes we are trialling are very destructive and leave very small amounts of testable material after decontamination.”

Previous work at this site by collaborators Dr Harry Langford and Professor Danielle Schreve and others has been crucial and will provide independent age control for the experimental radiocarbon dating.

Once the techniques for accurately dating seeds from this site have been established Dr Briant and her team will be able to go and reinvestigate other key sites of interest. There are several sites within the UK and the Netherlands where researchers have discovered that despite largely cold, arctic conditions there have been short periods of warmer weather. Until now, they have not been able to pinpoint when these periods fell, but with new techniques the answers may be about to be uncovered.