How Archaeologists Determine the Age and Authenticity of Ancient Artifacts

Determining how old an object is and whether it is genuinely ancient are two separate but related questions. Archaeologists answer the first with a mix of fieldwork observation and laboratory science, and the second by matching an object's materials and manufacturing marks against what is known to have been possible in its claimed period.

Step One: Relative Dating in the Ground

Before any laboratory test, archaeologists rely on stratigraphy, the study of soil layers. According to a teaching resource from Yale University's Human Relations Area Files (eHRAF), stratigraphy assumes that layers accumulate over time, so material found in a deeper layer is generally older than material above it. This is called relative dating: it establishes that one artifact is older or younger than another without producing a specific year.

Relative dating alone cannot say how many years separate two layers. For that, archaeologists turn to absolute dating methods, which the eHRAF resource describes as producing 'specific origin dates and time ranges, such as an age range in years.' Stratigraphic sequencing and absolute methods are normally used together, with the soil layers providing context and the scientific tests providing numbers.

Step Two: Putting a Number on the Age

Radiocarbon dating is the most widely used absolute method for organic remains. Living organisms absorb carbon-14 from the atmosphere; once they die, the isotope decays at a fixed rate. The radiocarbon laboratory Beta Analytic states that samples such as bone, teeth, charcoal and wood can be tested this way, and that laboratories and archaeologists need to agree on a sampling strategy before excavation to avoid contamination. Beta Analytic's facility now measures all submitted samples by accelerator mass spectrometry (AMS), which counts carbon-14 atoms directly rather than measuring their radioactive decay.

Carbon-14 has a half-life of 5,700 years, plus or minus 30 years, according to Wikipedia's summary of the accepted scientific value. Radiocarbon dating is generally limited to samples up to about 50,000 years old, though specialized preparation can sometimes push the method to 60,000 years or, in rare cases, close to 75,000 years before present, since beyond that point too little carbon-14 remains to measure reliably.

For wood, dendrochronology, the study of tree rings, can be more precise than radiocarbon dating. An Oxford University archaeology resource explains that trees lay down one growth ring per year, with width varying according to climate, and that overlapping ring patterns from different timbers let researchers build long regional reference sequences. In well-preserved samples, the source notes, the date a tree was felled can be narrowed 'almost to the week or day.' The method requires at least fifty years of rings to establish a reliable pattern, and it only works where a regional reference sequence already exists; the Oxford resource notes that many periods and regions, including the British Iron Age, lack one.

Fired clay objects such as pottery and bricks are dated differently, through thermoluminescence (TL). A guide published by the Archaeology Data Service explains that firing a pot in a kiln resets a natural radiation 'clock' inside its minerals to zero; afterward, the clay slowly re-accumulates energy from radioactive elements in itself and the surrounding soil. Measuring that stored energy and dividing it by the known annual radiation dose at the find site gives an age. The same guide notes that TL results are strongest when several measurements and techniques are combined rather than relying on a single reading.

Confirming Authenticity: Is It Really What It Claims to Be?

A scientific date is not the same as proof of authenticity. Specialists also examine how an object was made. A 2008 study by researchers from Cardiff University together with the British Museum, the Smithsonian Institution and Kingston University investigated two famous 'Aztec' crystal skulls, one held by the British Museum and one by the Smithsonian, according to a report from ScienceDaily. Using electron microscope analysis of tool marks, the team found that both skulls had been cut with rotary disc tools unknown in pre-Columbian Mesoamerica. Compositional testing additionally showed that the quartz used for the British Museum skull was quarried in Brazil or Madagascar rather than Mexico; the report did not state a quartz source for the Smithsonian skull. Researchers concluded, according to ScienceDaily, that the British Museum skull was made in 19th-century Europe, while the Smithsonian skull was made shortly before it was bought in Mexico City in 1960.

The crystal skull case illustrates a broader point: dating a material is not the same as dating when it was carved or assembled into its present form. The Archaeology Data Service's thermoluminescence guide notes that a recently fired object carries far less stored radiation energy than a genuinely ancient one, which is one reason the method can help flag objects made within the last century; it also recommends combining TL measurements with other techniques rather than relying on a single reading.

• Tool-mark analysis under a scanning electron microscope, to check whether the cutting or polishing technique existed in the claimed period, as used in the 2008 crystal skull study reported by ScienceDaily.
• Material-sourcing tests, to see whether stone, metal or pigment matches sources known to have been used in the claimed region and era, as with the quartz-origin testing on the British Museum crystal skull.

Why the Two Questions Are Linked

In practice, archaeologists and conservation scientists treat dating and authentication as complementary checks rather than a single test. A genuine ancient date from radiocarbon or TL analysis narrows down when the raw material existed; tool-mark and material analysis then help assess whether the object itself was shaped in that period rather than more recently from older material. The eHRAF teaching resource notes that combining relative and absolute methods gives archaeologists a fuller picture of an artifact's place in its original context.