Correlation between hydration and independent age estimate for cleaned data set, removing outliers and small samples, and correcting for elevation (source Eerkens et al. 2008).

Example of obsidian used in the study.

While there have been many studies that have questioned the veracity of obsidian hydration dating, the chronological technique had yet to be tested in southern Peru. Along with Jelmer Eerkens (the lead author in the study), Vaughn and several other colleagues (Tim Carpenter, Christina Conlee, Kathy Schreiber, Moises Linares Grados) compared over 230 obsidian hydration readings from 30 individual site components from the Southern Nasca Region (SNR). These site components included sites investigated during Proyecto Marcaya directed by Vaughn, Proyecto Nasca Temprano (ENCE) co-directed by Vaughn and Linares , Proyecto Nasca Sur directed by Schreiber, and Proyecto La Tiza and Proyecto Pajonal Alto directed by Conlee.

We were able to make independent age estimates of each hydration reading based on radiocarbon dates and temporally diagnostic artifacts. Although there were some problems with small sample sizes, readings needed to be adjusted for elevation, and the readings are source specific, a very strong relationship accounting for nearly 90% of the total variation in the data set was found. This suggests that obsidian hydration dating (OHD) works very well in the SNR and is a viable means of independently estimating age. Residual values from our regression suggest that hydration age estimates are usually within 15% of the radiocarbon estimates.

In the article published by the Journal of Archaeological Science, we present an equation other scholars can use to estimate age for Quispisisa obsidian in the SNR.

Full citation:
Eerkens, J. W., K.J. Vaughn, T.R. Carpenter, C.A. Conlee, M. Linares Grados and K. Schreiber (2008). Obsidian hydration dating on the South Coast of Peru. Journal of Archaeological Science 35:2231-2239. Click here for pdf.