A better idea of prehistoric diets

The University of Groningen Centre for Isotope Research (CIO) has been awarded funds to purchase new equipment for stable isotope analysis. The equipment will also make the CIO’s carbon-14 dating more accurate.

Dutch science funding agency NWO has awarded the CIO a grant of EUR 200,000. The CIO will use this to purchase what is known as an Elemental Analyzer, an instrument comprising equipment to incinerate samples together with an isotope-specific mass spectrometer that can measure stable isotopes of carbon, nitrogen and sulphur in the resulting gas. ‘It will replace the existing equipment that has reached the end of its lifespan’, CIO director Harro Meijer explains. ‘But the new equipment is also more versatile.’ The current analyzer cannot measure sulphur isotopes, for example.

Stable isotopes differ from their respective elements only in weight, as they have one or more additional neutrons. Chemically, all isotopes of an element are the same, but the difference in weight means they may be processed differently by living organisms. Plants, for example, prefer the ‘normal’ carbon-12 to the heavier carbon-13 isotope. This means plants will contain less carbon-13 than the atmosphere. Furthermore, isotopes may behave differently in physical processes. For example, water with a normal oxygen-16 atom will evaporate at a slightly different speed than water molecules carrying oxygen-18.

‘Different foodstuffs result in subtle differences in the ratio between stable isotopes’, Meijer explains. ‘So if you measure this ratio in the remains of animals or humans, you can make assumptions about their diet. And this in turn may tell us something about the climate in which the organism lived.’ The CIO uses this sort of measurement for prehistoric research.

The new equipment will be especially important for carbon-14 dating. ‘For this technique, you must first incinerate the sample and extract the carbon dioxide gas. This is turned into graphite, and we can then measure the carbon-14 content of this’, says Meijer. The new equipment reduces the carry-over of carbon from previous measurements, which can influence the results. ‘And to do a carbon-14 measurement, we also need to know the carbon-13 content. We can measure this in one go with the new equipment.’

The CIO has been world-renowned as a reference lab for carbon-14 dating for decades now. Some of its staff, together with a number of international colleagues, recently published a new calibration curve for carbon-14 dating, and the CIO does a lot of work for archaeological research. ‘And sometimes we are called upon by the Netherlands Forensic Institute, if they need to know whether human remains that have been found are from a recent murder case or centuries old.’