Applying Stable Isotopes in Archaeology: A History
The application of stable isotope analysis to archaeological questions is about 30 years old. The first published archaeological study was by J.C. Vogel and N.J. van der Merwe in 1977 ("Isotopic evidence for early maize cultivation in New York State." American Antiquity 42:238-242). They compared the stable carbon isotope ratios (13C/12C) in the collagen of human ribs from an Archaic (2500-2000 BC) and an Early Woodland (400-100 BC) archaeological site in New York with the 13C/12C ratios of ribs from a Late Woodland (ca. 1000-1300 AD) and Historic Period site from the same area. They were able to show that maize was not present in the early periods, but had become a staple food by the time of the Late Woodland.
Based on this demonstration and available evidence for the distribution of the stable carbon isotopes in nature, Vogel and van der Merwe suggested that the technique could be used to detect maize agriculture in the Woodlands and tropical forests of the Americas; determine the importance of marine foods in the diets of coastal communities; document changes in vegetation cover over time in savannas on the basis of browsing/grazing ratios of mixed-feeding herbivores; and possibly to determine origins in forensic investigations.
New Applications of Stable Isotope Research
Since 1977, applications of stable isotope analysis have exploded in number and breadth, using the stable isotopes ratios of the light elements hydrogen, carbon, nitrogen, oxygen and sulfur in human and animal bone (collagen and apatite), tooth enamel and hair, as well as in pottery residues (baked onto the surface or absorbed into the ceramic wall) to determine diets and water sources. Light stable isotope ratios (usually of carbon and nitrogen) have been used to investigate such dietary components as marine creatures (e.g. seals, fish and shellfish), various domesticated plants such as maize and millet; cattle dairying (milk residues in pottery), and mother’s milk (age of weaning, detected in the tooth row). Dietary studies have been done on hominins from the present day to our ancient ancestors Homo habilis and the Australopithecines.
Other isotopic research has focused on the geographic origins of things. Various stable isotope ratios in combination, sometimes including the isotopes of heavy elements like strontium and lead, have been used to determine whether the residents of ancient cities were immigrants or were born locally; to trace the origins of poached ivory and rhino horn to break up smuggling rings; and to determine the agricultural origins of cocaine, heroin, and the cotton fiber used to make fake $100 bills. The latest wrinkle involves the potential use of hydrogen and oxygen isotopes in hair to determine where a person has been lately, by comparing the measurements with an international database for rainfall and local water supplies.
Another example of isotopic fractionation that has a useful application involves rain, which contains the stable hydrogen isotopes 1H and 2H (deuterium) and the oxygen isotopes 16O and 18O. Water evaporates in large quantities at the equator and the water vapor disperses to the north and south. As the H2O falls back to earth, the heavy isotopes rain out first. By the time it falls as snow at the poles, the moisture is severely depleted in the heavy isotopes of hydrogen and oxygen. The global distribution of these isotopes in rain (and tap water) can be mapped and the origins of the consumers can be determined by isotopic analysis of hair. (Watch our for skinheads arriving from the Axis of Evil!)
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Many thanks to Nikolaas J. Van der Merwe for much needed assistance with this article.