Changes in Prehistoric Land Use in Alpine Sierra Nevada: A Regional Exploration Using Temperature-Adjusted Obsidian Hydration Rates. Journal of California and Great Basin Anthropology 25:187-205.
Stevens' (2005:192) proposed hydration rate is t = [1 / (8.2694 * 10 11 * e -7268.2 / T)] * x 2 , in which "t" is the elapsed time, in thousands of calendar years; "T" is the Effective Hydration Temperature (EHT), in degrees Kelvin; and "x" is the thickness of the hydration rind, in microns. For purposes of comparison, in the timeline the EHT is taken as 20.4 o C (293.56 o K) and the time that the hydration reading was made is taken as A.D. 2000. Expressing the elapsed time in years, the rate formula becomes t = 40.32 x 2.
The timeline does not include adjustments for local temperature history, which may substantially affect the results. It also does not take into account other possibly significant factors such as humidity or intra-source chemical variability.