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  • Educator Farnaz Khatibi Jafari
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In archaeological studies of human migration, stable isotopic tracers have been employed for mapping movements of species and materials. Since the 1980s, chemical analysis (trace elements, radiocarbon dating, isotopic studies) have been used frequently in archaeological investigations of prehistoric population. Strontium, oxygen, and lead are three elements indicating possible residential/material changes.

Oxygen is the most abundant element on Earth. Oxygen-18 in minerals can help indicate ancient water temperatures and evaporation cycles. Because the oxygen isotope value in mammalian tissues (like tooth enamel) varies according to the water ingested during an organism's lifetime, it reflects the composition of precipitation where it lived. 

Strontium is a trace element found in metamorphic rocks, sedimentary rocks, and natural materials. Strontium has four naturally-occurring isotopes: three non-radiogenic isotopes, Strontium-84 (0.560%), Strontium-86 (9.870%), and 88Sr (82.53%), and one radiogenic isotope, Strontium-87 (7.040%), which is formed by the radioactive decay of Rubidium-87. In natural materials, strontium isotope composition (Strontium-87/Strontium-86) is generally between 0.700 and 0.750. Rocks older than ten million years have higher Strontium-87/Strontium-86 fractionation because of their large atomic mass.

Mammalian, including human, tooth enamel (hydroxyapatite) has an isotopic signature derived from food digested during an organism’s lifetime. This information helps provide insight regarding the food web, diet, and trophic level. The strontium signature of bedrock is transferred by streams to the soil, from the soil into plants, and from plants into the food web with minimal isotopic fractionation. 

Some suggested resources from the author of this lesson include: Stable Isotope Analysis of Humans , Isoscapes: Understanding movement, pattern, and process on earth through isotope mapping, and ANALYTICAL CHEMISTRY IN ARCHAEOLOGY.