Three Dates for Two Layers: Budgeting Chronology at a Birbhum Site
A second-year HS student joins a college excavation at a multi-period site near Suri, Birbhum. The cleaned section shows Layer A (0–0.5 m) with red ware and a shouldered stone celt, and Layer B (0.9–1.4 m) with microlithic blades, a compact hearth, and fragmentary animal teeth. A later pit, P1, cuts from Layer A down through Layer B. The student recovers four datable items: charcoal from the hearth, a second charcoal spread 20 cm away, a tooth from Layer B, and a red-ware sherd at 1.1 m that looks like Layer A pottery. The laboratory charges ₹6,500 per radiocarbon date and the project can afford only three. The tooth is fragile and collagen preservation is unknown. The site director wants 'the oldest date' for a press release, and the local media have already called the site 'India's earliest village'.
1. Which three items should be submitted for dating, and which should not? Justify each choice using stratigraphy, material suitability and the position of pit P1.
Read the worked answer
The test is secure association, not simply whether a material is organic.
- Hearth charcoal (first choice): short-lived material in a sealed, compact hearth directly associated with the Layer B occupation. It dates the use of the hearth, not old timber.
- Second charcoal spread (second choice): useful as a replicate only after checking whether it lies within the hearth or in a separate lens; if it is within 30–40 cm of P1, treat it as suspect.
- Tooth (conditional third choice): submit only after collagen screening (% yield, C/N ratio). If preservation is poor, the money is wasted; if good, it gives a direct faunal association.
- Red-ware sherd (do not submit): pottery is inorganic and cannot be radiocarbon dated. Typologically it resembles Layer A, so it is probably intrusive down P1 or through root action. Dating it would date an object, not the layer.
- Stone celt (do not submit): not datable by radiocarbon; useful only for typology.
So submit two charcoal samples plus the tooth, and state in the report that all three are tied to their stratigraphic positions.
2. The two charcoal dates come back inverted, with the upper sample older than the lower one. Without extra money, how should the student interpret and report this?
Read the worked answer
An inversion means at least one date, or one association, is wrong. Do not average the two and do not select the older one.
- Check the laboratory record: δ13C, C/N, % carbon, pre-treatment and yield. A low yield or contamination is a technical reason to reject a result.
- Check context: the upper charcoal may be old wood from a long-lived tree; it may lie near P1; roots or burrowing animals may have moved material; the hearth may include residual charcoal.
- Use stratigraphy as an independent check: Layer B lies below Layer A, so an upper date older than the lower date is the one to suspect.
- Report both with lab codes, material and calibrated 2σ ranges, and mark one as a rejected outlier with the reason.
- State the best estimate from the stratigraphically consistent date, and describe it as a provisional terminus for Layer B, not a fixed age.
The report should say that the chronology is provisional and that a charred seed or a second hearth would be needed to resolve the inversion.
3. How should the student respond to the director's request for 'the oldest date' and to the media claim that the site is 'India's earliest village'?
Read the worked answer
The request confuses a date with a headline. A radiocarbon result is a calibrated range with an error term; choosing the oldest of three results is cherry-picking and misrepresents the method.
The student should:
- give the director a table of all three results, with material, lab number, uncalibrated age, calibrated range and whether the sample was accepted or rejected;
- draft a sentence such as: 'Charcoal from a sealed hearth in the lower layer dates to X–Y cal BP; the upper layer is later but still poorly dated';
- explain that 'India's earliest village' requires comparison with dated sites across the region, a secure definition of 'village', and evidence of permanent architecture, not one hearth;
- advise the director to avoid 'earliest' and use 'one of the earlier dated occupations in the district' until more work is done;
- ask that the press release include the laboratory and the error range, so the claim can be checked.
Refusing the 'oldest' framing is not obstruction; it protects the project from a correction later.