Where you grew up, what you ate—your bones record your life

Archaeologists use isotopic analysis to determine population movements and diets from chemical signatures in ancient human remains.

Published 19 Jul 2019, 14:13 BST
A Christogram – an archaic abbreviation for the name of Christ – made of human bones and ...
A Christogram – an archaic abbreviation for the name of Christ – made of human bones and skulls in the Sedlec Ossuary near Kutna Hora, Czech Republic. But as well as used as – albeit bizarre – literal recording such as this, our bones record in other ways.
Photograph by VPC Photo, Alamy

What’s on your plate? The answer doesn’t just matter for your next dinner—it’s an issue of critical importance to archaeologists, who can infer everything from individual diets to large-scale population movements based on the chemistry of an ancient bone sample. Stable isotope analysis, the study of the nuances of elements in archaeological materials, can unlock all sorts of secrets about climate, diet, and the geographical origins of bones and other materials.

Stable isotopic analysis looks at the isotopes—atoms with extra or missing neutrons—of different elements. Unlike unstable isotopes such as carbon-14, which degrades over time, stable isotopes never decay. There are over 250 known stable isotopes, and 80 of the periodic table’s first 82 elements have them. Both organic and inorganic compounds contain these isotopes, and their ratios relative to one another act like a signature. (Learn how carbon isotopes help date ancient objects.)

Carbon dating isn't a silver bullet for dating – but it can help archaeologists unpick the mysteries of past diets, climate conditions and lifestyles, as well as date remains.

Solving ancient mysteries

In the 1970s, archaeologist Nikolaas van der Merwe uncovered a skeleton that did not look like the others at the South African site he was excavating. Together with isotope physicist John Vogel and palaeoanthropologist Philip Rightmire, he decided to apply new scientific techniques with isotopes to the skeleton. The analysis revealed the ancient human had a different diet from others discovered during the excavation, which suggested previously unsuspected interactions between hunter gatherers like the people uncovered at the site and farmers in the region.

Van der Merwe and Vogel went on to use stable isotope analysis on archaeological materials from the United States to show that maize had been introduced in the Eastern Woodland region of North America around 1,000 A.D.

Archaeologists unwrap a child sacrifice from the mass burial at the Pampa La Cruz site in Peru. Analysing the child's bones can give archaeologists insight as to why this ancient civilisation sacrificed their children.
Photograph by Mark Thiessen, Nat Geo Image Collection

Isotope signatures are extremely useful for researchers. For example, plants absorb stable carbon-12 and carbon-13 isotopes, which have a consistent ratio to one another in Earth’s atmosphere. That ratio is passed on to plants through the soil and water they absorb. During photosynthesis, the amount of water, sun, and other factors changes the plants’ carbon isotope ratio. 

There are three categories of carbon ratios for plant photosynthesis: C3, C4, and CAM. Each tells researchers something about where the plants were cultivated and what kinds of environmental conditions they endured. As plants are ingested by animals, they become part of their bodies. In turn, analysing the amount of carbon in animal hair, teeth, and bones shows the ratio of carbon isotopes contained in the plants they consumed.

That can reveal their photosynthesis types, which points to what kinds of plants an organism ate and which environmental conditions created them. Isotopes can also point to weather conditions sustained by an individual (people who live in arid environments, for example, contain more nitrogen-15) or suggest how populations moved.

Snapshots in time

Other isotopes reveal all sorts of information about archaeological materials. Strontium isotopes are absorbed into teeth during their creation, creating a snapshot of sorts of where an individual lived during their childhood. But bone cells turn over constantly, gathering strontium signatures that reflect where individuals lived later.

Comparing the two can reveal movement over an individual’s lifespan or show that an individual wasn’t born at the site at which they were recovered. And nitrogen isotopes can reveal how old a child was when he or she started eating solid foods. 

Stable isotopes are now used to study everything from bones to food residues on pots. They can also be used to identify the source of different metals.

But isotope analysis isn’t a silver bullet—it’s expensive, the technique does not work on materials that have been burned, and contamination must be carefully avoided. And the older the specimen, the less that can be inferred from it, since bone collagen breaks down after about 50,000 years. Still, atoms can tell plenty about the origins and behaviors of the people whose burial sites have become archaeological digs.

Read More

You might also like

Science and Technology
Radiocarbon helps date ancient objects—but it's not perfect
Science and Technology
This man drowned 5,000 years ago. How do we know that?
Science and Technology
Everest’s highest glacier has lost 2,000 years of ice in 30 years
Science and Technology
The Tonga eruption explained, from tsunami warnings to sonic booms
Science and Technology
5 ways Jacques Cousteau pushed to protect the planet

Explore Nat Geo

  • Animals
  • Environment
  • History & Culture
  • Science
  • Travel
  • Photography
  • Space
  • Adventure
  • Video

About us


  • Magazines
  • Newsletter
  • Disney+

Follow us

Copyright © 1996-2015 National Geographic Society. Copyright © 2015-2021 National Geographic Partners, LLC. All rights reserved