Stable isotope analysis provides insight into geographic origin or travel history because isotopic ratios reflect what?

• A. Isotopic ratios reflect local water and diet signatures, helping to infer geographic origin or travel history
• B. They provide no information relevant to origin
• C. They indicate postmortem interval precisely
• D. They are used to identify disease states

Answer: (A)

Stable isotope analysis works because the isotopic ratios in a person’s tissues reflect the environment they grew up in or moved through, due to the local water, diet, and geology shaping those ratios. Water in different regions has distinct hydrogen and oxygen isotope values, and the foods people eat carry carbon and nitrogen signatures tied to local ecosystems. Geological differences also leave a distinctive strontium isotope pattern in tissues that form during life. Because tooth enamel forms at specific childhood times and bone continually remodels, the isotopic record can point to geographic origin and track travel history.

That’s why describing isotopic ratios as reflecting local water and diet signatures, which in turn map onto geography, is the best answer. The other statements misstate the utility of stable isotopes: they don’t provide no information, aren’t used to pin down a precise postmortem interval, and aren’t used to diagnose disease states.