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Isotope Analysis: You Are What You Eat (and Where You Lived)
Quality reviewed September 2026
Facts verified September 21, 2026
- Subject
- Social Studies
- Grades
- Grades 9-12
- Length
- 9-page student worksheet
- Time
- About one 50-minute class period
- Great for
- Sub plans and independent work
- Includes
- Reading passage, comprehension questions + full answer key
- Format
- Print-and-go PDF
What students do
- Match five terms, including strontium, tooth enamel, and isotope analysis, to their definitions
- Strontium locked into childhood tooth enamel never changes again, which is exactly what convicts a York skeleton of a North African childhood
- Explain why tooth enamel, not bone, is used to trace where someone spent their childhood
- The Amesbury Archer's isotope signature placed his childhood in Alpine Europe despite his burial near Stonehenge
What it covers
- How strontium locked into tooth enamel during childhood reveals where a person grew up
- Why the Amesbury Archer's isotope signature placed his childhood in Alpine Europe, not near Stonehenge
- What carbon and nitrogen isotopes in bone collagen reveal about ancient diets, from maize farming to marine protein
Start reading this worksheet
What Are Isotopes and Why Do They End Up in Bones?
Every chemical element exists in multiple forms called isotopes, versions of the same element with the same number of protons but different numbers of neutrons. Most isotopes are stable, meaning they do not decay radioactively. Because different isotopes of the same element have slightly different masses, living organisms incorporate them into their tissues at different rates depending on diet and environment. Over the course of a lifetime, the isotopes an animal or person consumes through food and water become literally incorporated into the molecules of their bones and teeth. When those bones are preserved for centuries or millennia, the isotopic signatures they contain can be analyzed by archaeologists to reconstruct diet, geographic origin, and migration patterns. The key insight is that isotopic ratios in bone and tooth are not random: they reflect the isotopic composition of the environment where a person lived and the foods they ate. Different regions of the world have characteristically different isotopic signatures based on their geology, climate, and food chains. By comparing the isotopes in ancient bone to the known isotopic signatures of different environments, researchers can make confident inferences about where a person grew up and what they ate. The technique has become one of the most powerful and versatile tools in bioarchaeological analysis.
Strontium: The Geographic Tracker
Strontium isotope analysis is perhaps the most powerful tool for reconstructing geographic mobility. Strontium is a naturally occurring element found in soil and water, and its isotopic ratio varies predictably across different geological formations. Plants absorb strontium from the soil they grow in. Animals and humans absorb strontium from the plants and water they consume. That strontium is then incorporated into tooth enamel as it forms during childhood. Once enamel is formed, it does not remodel or change. This means that the strontium ratio in a person's tooth enamel is a permanent record of the geology of the region where they spent their childhood, regardless of where they later moved or where they were buried. This has made strontium analysis a powerful tool for identifying migrants in ancient burial populations. If a skeleton is found in a Roman cemetery in England but its tooth enamel strontium signature matches the geology of North Africa rather than Britain, that person almost certainly did not grow up in England. Strontium analysis has revealed that Roman cities were far more cosmopolitan than traditional historical accounts suggested, with individuals buried in the same cemeteries having grown up in locations spanning from Scotland to the Sahara.
Carbon and Nitrogen: Reading Ancient Diets
While strontium tracks where you lived, carbon and nitrogen isotopes track what you ate. Different types of plants fix carbon differently during photosynthesis. C3 plants, which include wheat, barley, most European crops, and the majority of temperate-zone vegetation, have a lower ratio of carbon-13 to carbon-12 than C4 plants, which include maize, sorghum, and millet. Because these isotopic signatures pass up the food chain, the carbon isotope ratio in human collagen (extracted from bone) reflects the proportion of C3 versus C4 plants in a person's diet. This allowed researchers to track the adoption of maize agriculture across the Americas by measuring when carbon isotope ratios in human bone shifted toward C4 values. Nitrogen isotopes work differently: their ratio in bone collagen reflects an individual's position in the food chain. Nitrogen-15 becomes enriched at each trophic level, meaning that carnivores have higher nitrogen-15 ratios than herbivores, and humans who ate large amounts of animal protein have higher ratios than those who subsisted primarily on plant foods. In coastal populations, marine protein (from fish and shellfish) produces particularly elevated nitrogen-15 ratios because ocean food chains are longer than terrestrial ones. This allows researchers to distinguish, for example, whether inland prehistoric peoples were primarily farmers or relied heavily on fishing.
Like what you read? The full reading, the case study, and every question set are in the free download below, along with the answer key.
Why this matters
Isotope analysis answers a question students ask about their own lives without realizing it is a scientific one: where did you actually grow up, and what does your body still carry from it. The Roman York case study pushes back on the assumption that ancient cities were made up of people who never left home, since the man buried there carried a permanent chemical record of a childhood spent near the Sahara. This reading also gives students a clean example of how much confidence scientists can have from chemistry alone, and where that confidence runs out, since isotopes can show where someone lived but never why they moved there.
From one teacher to another
Teeth remember things bones forget, and this reading uses that fact to explain how isotope analysis reconstructs where a person grew up and what they ate. Strontium locks into tooth enamel during childhood and never changes afterward, which is how researchers proved that a man buried in Roman-era York had grown up near the Sahara, not in Britain. Carbon and nitrogen isotopes work on bone collagen instead, tracking whether someone ate mostly C3 crops like wheat or C4 crops like maize, and how much animal protein made up their diet. The reading closes with two well-documented cases: the Amesbury Archer, whose enamel showed he grew up in Alpine Europe despite being buried near Stonehenge, and Richard III, whose isotopes shifted toward a richer diet in the years after he became king. The case study follows bioarchaeologist Tomas Reyes as he confirms a York skeleton's North African origin and rethinks what a Roman city actually looked like.
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