Diet of ancient populations
Methods to understand the diet of our ancestors have been diversifying for more than a decade in archaeology, but also in anthropology thanks to new physicochemical techniques.
In this article, we will discuss the use of stable carbon and nitrogen isotopes (δ13C and δ15N) present in bone collagen. Using these methods, it is possible to learn about the environment from which individuals drew their resources, as well as their relative places in the food web. With stable isotope analysis, we understand the food choices of a group, but we also detect socio-cultural and economic distinctions. Our laboratory scientists propose an individual and collective dietary pattern based on information from each individual.
Determining diet with stable isotopes of carbon and nitrogen
Carbon-14 dating is not the only technique used in archaeometry. The analysis of stable isotopes of carbon and nitrogen also provides a great deal of information. Regarding plants, our scientists distinguish two types of photosynthesis:
- In C3 for woody trees, rice, cotton or even wheat that have a δ13C lower than -20 ‰;
- In C4 as grass, corn or even sugarcane that have a δ13C between -10 and -20%.
We also use the isotopic ratio of nitrogen 15 and 14 to determine the origin of proteins.
Thanks to the stable isotopes of carbon and nitrogen, it is possible to know the diet of a person or an animal. Knowing, for example, whether he or she was a carnivore, herbivore or omnivore. We can also determine whether the diet was more terrestrial or marine in origin.
Determining the state of conservation of bone material, an important step in exploiting the samples
Through the quantification of carbon and nitrogen concentrations and the analysis of the C/N ratio, it is possible to apprehend the state of conservation of the organic bone material, collagen. A bad state of conservation of collagen will not allow the exploitation of the samples. Only a C/N in the range of 2.9 to 3.6 will reveal a state of preservation compatible with a reliable carbon-14 dating and isotopic study.
Interpretation of results
The results of carbon and nitrogen stable isotope analysis provide valuable information such as:
- The provenance of animal proteins (meat, milk/former or fish dominance);
- Importance of cereals and legumes in ancient times.
It is also possible to compare the results with different groups of individuals to detect different habits and to understand archaeological issues. Our scientists interpret the results and collaborate in solving your hypotheses.
The CIRAM laboratories use a vario ISOTOPE select elemental analyzer (EA) from ELEMENTAR that measures carbon and nitrogen concentrations ( tomic). It is a high-temperature combustion unit, up to 1200 °C. The weighing range is from 20 µg to 300 mg. The concentration range is up to 7 mg absolute for carbon and up to 10 mg absolute for nitrogen. The external accuracy (1s) is less than 0.1% for carbon and nitrogen. The elemental analyzer is the gas injection system in the IRMS. The IRMS isoprime precisION from ELEMENTAR is an isotope ratio mass spectrometer that measures the stable isotope ratios of carbon (13C/12C) and nitrogen (15N/14N) expressed in per thousand (‰). The external precision (1s) is 0.1 ‰ for δ13C and 0.15 ‰ for δ15N.
CIRAM, a leader in dation and analysis since 2005
Stable isotope analysis is a goldmine for understanding the dietary and social habits of a group of individuals, but to be reliable it is important to perform them on a significant corpus of individuals, otherwise the results cannot be representative.
CIRAM, dating and laboratory analysis since 2005, accompanies all its results with a complete and documented report. Our teams of researchers are at your disposal and close to your field realities.