Stable Isotopes and Archaeology
Stable isotope analysis is a fast-growing research tool in archaeology and related fields. It relies on natural biological processes that occur when humans eat or drink animal and plant fibers and liquids. To put it simply, in the process of ingesting food, humans, animals and plants absorb elements from their surroundings, including different forms or isotopes of elements such as strontium. Elements occur in the natural environment in multiple forms, with varying atomic weights; for a few elements, the ratio of one form over another varies from place to place, and it is that ratio that gets communicated up the food chain. For a detailed description of how this process works, see the article called The Natural Processes of Stable Isotopes.
Several elements are used in stable isotope analysis, including carbon, oxygen, lead, and strontium. Strontium in particular substitutes for calcium in the mineral portion of human and animal bones and teeth (called hydroxyapatite).
Of course, the intake of nutrients continues throughout the life of an animal, plant or human. So, if someone migrates to another region, his or her bone chemistry soon changes to reflect the local environment. However, human teeth have something that human bones don’t: a layer of enamel, which forms in children’s teeth by the age of 2 or 3. Once formed, enamel is inert, and retains the chemical signature obtained by the child from birth to age three throughout a person’s life, and luckily for us, afterwards. In other words, information concerning our region of origin—or at least the chemical makeup of the geology of our homeland—is hardwired into the enamel of our teeth.
Campeche and the Slave Factory at Elmina
As a result of their analyses, Price and Burton determined that the chemical ratio of two isotopes of strontium revealed in the teeth of the individuals with tooth modification resembled the value found in the teeth of local residents in the vicinity of the town of Elmina, a Portuguese colony in Ghana, west Africa. Elmina was founded in 1482 as Fort São Jorge da Mina and is notorious as one of the slave factories on the west African coastline. This result tends to support the original suggestion that these four individuals were born in West Africa.
Although the strontium ratios are comparable to those found in the Elmina region, stable isotope analysis did not rule out other locations in the world with similar geochemical characteristics; and there is no certain evidence as of yet that the Africans were slaves. It is possible that these four individuals came to the New World as free people.
The Earliest African-Americans
There were also several individuals in the cemetery with evidence of African tooth modification but whose isotopes indicated a birthplace in the region of Campeche. Thus these individuals are among the earliest known African-Americans in the New World.
Related News Stories
- Excavated Teeth Likely Came from First Africans Brought to the New World, from the National Science Foundation
- At Burial Site, Teeth Tell Tale of Slavery. John Noble Wilford in the NYT.
Thanks to T. Douglas Price for his assistance with this article.
