Dating methods obsidian hydration

FIGURE 88 Dating methods. Shortly after the discovery of radioactivity, at the beginning of the twentieth century, it was found that the decay of radioactive elements could be used to keep track of time. Many of the dating techniques developed since then are, therefore, based on radioactive decay phenomena, but others, such as the hydration of obsidian, amino acid racemization, and dendrochronology, are based on other physical, chemical, or biological phenomena. 

Liritzis, I. (2006), SIMS-SS A new obsidian hydration dating method Analysis and theoretical principles, Archaeometry 48, 533-547. 

The rate of hydration of obsidian, which is diffusion limited, forms the basis for Obsidian Hydration Dating [f]. A date refers to "the time a fresh surface of obsidian was created, either naturally or by man.. ..Laboratory and field studies have confirmed that the time indicated by a hydrated layer is proportional to the thickness squared of the layer. The hydration rate is independent of the relative humidity of the environment, but the chemical composition of the obsidians affect the rate by orders of magnitude. Si02 increases the rate, whereas CaO, MgO, and H20 decrease it. A 6 - 8 °C temperature increase causes doubling of the rate." The method is quite inexpensive, and it is applicable to ages between a few hundred and several million years. 

Attempts to apply thermoluminescence (TL) and electron spin resonance (ESR) data to date soil horizons, and to use ESR to date bone are underway. As yet, there are no agreed-upon criteria on which to evaluate the overall reliability of age inferences based on ESR data (13). It has been suggested (14) that in some circumstances the obsidian hydration method can be used to infer chronological age over in excess of 100,000 years (14). However, obsidian is not a widespread natural resource and some of the hydration rate structures appear to yield problematic results. Amino acid racemization (AAR) values can be used under some conditions to infer accurate age values for bone, but seriously anomalous values can be obtained (15, 16). The conditions under which AAR values can be used to accurately infer age, particularly for bone samples, continue to be investigated. 

Liritzis, L, Laskaris, N. (2009) Advances in obsidian hydration dating by secondary ion mass spectrometry world examples. Nucl. Instrum. Methods B, 267,144. 

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