Author ORCID Identifier

https://orcid.org/0000-0003-4391-3590

Document Type

Article

Publication Date

7-2026

Keywords

Obsidian hydration dating, Bayesian modeling, uncertainty quantification, Rapa Nui, Easter Island, IR-PAS, radiocarbon dating

Subject Heading(s)

Archaelogy

Abstract

Obsidian hydration dating (OHD) measures water absorption into volcanic glass to estimate artifact age. Recent studies using infrared photoacoustic spectroscopy (IR-PAS) claim ±30-year precision, comparable to radiocarbon dating. We tested these claims by applying Bayesian hierarchical models to 242 published IR-PAS measurements from Rapa Nui (Easter Island). Standard OHD practice treats burial temperature and humidity as known constants; we instead modeled them as uncertain variables and propagated that uncertainty through the rate equation. Realistic dating uncertainties are ±300 years, ten times larger than the claimed value. The 95% credible interval for any individual date (~600 years) exceeds Rapa Nui's entire prehistoric sequence (~520 years). Cross-sensitivity analysis reveals a dual bottleneck: even with perfect spectroscopic measurement, unknown burial conditions alone produce ±184 years of irreducible uncertainty. Independent validation using Bayesian phase models shows that OHD dates contradict known stratigraphy at two excavated sites: adding OHD to radiocarbon worsens chronological prediction rather than improving it. Consequently, sub-centennial archaeological claims built on these dates, such as assertions of pre-contact population decline, distinguishing cultural phases, or correlating activity with environmental change, cannot be sustained. The limitation is epistemological, not technological: accurate OHD requires knowing each artifact's complete burial history, information that archaeological excavation cannot provide. These constraints apply wherever OHD is practiced in contexts with environmental variability.

Creative Commons License

Creative Commons Attribution-Share Alike 4.0 International License
This work is licensed under a Creative Commons Attribution-Share Alike 4.0 International License.

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