How a tooth can hold clues to where someone grew up

In 2025, researchers reported measurements from the teeth of 71 people buried at five Neolithic sites in what is now Syria. The individuals had lived thousands of years before passports or birth certificates. Their enamel helped the researchers test whether their childhood diets fitted the environments around the burial sites. Some possible newcomers received burial treatment much like people whose results were compatible with the local environment. Read the primary study.

That is a remarkable thing to ask of a tooth. How can something in your mouth carry information about a landscape? The answer begins underground, travels through meals, and ends with a comparison, not a hidden address.

From rocks to dinner

Rocks contain small amounts of strontium, a naturally occurring element. Its atoms come in different versions, called isotopes: they have the same number of protons but different numbers of neutrons. Archaeologists commonly compare strontium-87 with strontium-86, writing the result as 87Sr/86Sr. The ratio describes the relative abundance of the two isotopes, not simply how much strontium a sample contains. IUPAC explains natural strontium isotope variation.

The pattern begins with geological history. Strontium-87 is stable, but some of it formed through the very slow radioactive decay of rubidium-87. A rock's age, origin and chemical composition can therefore affect its ratio. Old, rubidium-rich rocks often have higher ratios than young volcanic rocks, although “old means high” is not a universal rule. This is not radioactive strontium passing from rocks into children. A 2025 scientific review explains the geological relationship.

As rocks weather, strontium enters soil and water. Plants take it up; animals eat plants; people eat plants and animals. Rivers can bring material from upstream, wind can deliver dust, and sea spray can add strontium from the ocean. Drinking water can also contribute. The mixture available to living things is called bioavailable strontium. It is not necessarily identical to the ratio in the rock directly beneath a house.

Foods also contain different amounts of strontium, so their influence is not proportional only to how much food someone ate. Imported grain, livestock raised elsewhere or water from a different source can alter the mixture. A large baseline study in southern Sweden shows why researchers examine plants, waters or small animals rather than treating a geological map as a ready-made human map. Read the open baseline study.

A landscape enters a tooth through food

Strontium behaves enough like calcium to enter the mineral that makes teeth hard. Tiny amounts become incorporated into enamel while a tooth crown forms. Once mature, enamel does not continually rebuild itself as bone does. A surviving sample can therefore preserve a chemical record from childhood rather than the person's final years. A 2025 scientific review follows strontium from environment to tissue.

Different teeth develop at different times. An early-forming tooth and a later-forming tooth can offer windows into different parts of childhood. Formation is not the same as eruption: a tooth can be developing inside the jaw before it appears in the mouth. A sample also averages inputs over part of the formation and maturation period. It is not a diary that dates each meal or move. Explore the Queen Mary University of London tooth-development atlas.

This is why the everyday question needs careful wording. A tooth can reveal something about the sources of childhood food and drink. If those sources were mainly local, the result can help test where someone grew up. It does not directly identify a birthplace, town or journey.

That pathway is biological as well as geological. The material must reach food or water, enter the body, and become part of forming enamel before a laboratory can measure it.

Reading the number

The laboratory starts with a carefully chosen piece of enamel. In one common approach, researchers remove potentially contaminated surfaces and any adhering dentine, the softer tooth tissue beneath enamel. They dissolve the cleaned sample and chemically separate its strontium. A mass spectrometer, an instrument that separates charged atoms by mass and compares their signals, measures the isotope ratio. Reference materials help check the result. Other sampling methods exist, so this is an example workflow rather than a universal recipe. See an open archaeological methods paper.

A precise number is only half the job. Researchers also need to know what ratio a person eating locally might have acquired. They build a bioavailable baseline from environmental samples suited to the landscape and question. These measurements can become an isotope map, or isoscape.

The British Geological Survey's current map for Great Britain draws its strontium layer from roughly 1,300 samples, predominantly plants and water. It shows expected regional variation rather than assigning one magic value to every point. The enamel result is compared with that environmental evidence. Examine the BGS Biosphere Isotope Domains.

A match is not an address

If a tooth's ratio falls outside a well-supported local range, it can be evidence that the person's childhood food came from another geological environment. If the person was later buried at the site, movement is one explanation. Imported food is another, and a weakly sampled baseline can make “non-local” look more certain than it is.

A match is weaker than it first sounds. Distant places can share similar ratios, so someone could move between them without leaving a detectable difference. A result inside the burial area's range means a local childhood is compatible with the evidence; it does not prove the person never travelled. The method is often better at ruling out a proposed origin than choosing one unique homeland. BGS explains why map matches are areas that cannot be excluded.

Archaeologists therefore combine strontium with other clues. Oxygen isotopes can add information related to ingested water, while burial context, artefacts, ancient DNA and other evidence address different parts of a life. The Syria study used strontium and oxygen together. One enamel ratio was not treated as a complete biography.

Jonathon Ericson published a model for investigating past residence with strontium isotopes in 1985. Later work has improved sampling, laboratory methods and the environmental baselines needed to interpret the measurement. Read the original paper's abstract.

The achievement is not that teeth remember an address. It is that a childhood tissue can preserve evidence connecting a person to the landscapes that supplied their food. With a strong baseline and other archaeological clues, that evidence can show which stories about a life still fit, and which do not.