For the past six weeks or so, I've been attempting to get up to speed on the current status of what scholars believe about the timing of the first human occupation of the Americas. There are at least four scholarly theories about the event or events, and each of those theories is complicated by problems of archaeological dating. Trying to be both precise and clear about dates has not proven easy, partly because radiocarbon dates are sometimes reported calibrated and sometimes not. That's not the fault of the researchers, necessarily; calibration for dates older than 11,500 BP was only available beginning in 2004. And it turns out that c14 dates are not the only ones that need calibration. But, mostly I'm not getting the article written because I keep getting distracted by interesting side issues. Case in point: Ushki Lake.

The Ushki Lake sites are five sites on the Kamchatka Peninsula of Siberia--part of Beringia and thus important for understanding the original peopling of America. The earliest dates on the lowest components were reported as 16,800 cal years BP; but recent tests have revised that date to about 13,500 cal years BP. While I was compiling notes for the piece on Ushki, I found a new article coming out this year in the Journal of Archaeological Science, about sourcing the obsidian at Ushki.

In Obsidian use at the Ushki Lake complex, Kamchatka Peninsula (Northeastern Siberia): Implications for terminal Pleistocene and early Holocene human migrations in Beringia, Yaroslav Kuzmin and colleagues report there are between four and six different sources for the obsidian discovered from the earliest levels at Ushki Lakes--and the sources are between 200 and 300 kilometers away from the sites. Now that's interesting--because it illustrates long range resource procurement strategies. That's something you would expect for Terminal Upper Paleolithic/Late Pleistocene hunter-gatherers. But I wondered why the scholars didn't use the obsidian for dating purposes--obsidian hydration is a fairly inexpensive dating technique that's readily available: why not, I thought, back up the dates with a hydration date?

I hadn't gotten around to asking anybody when I ran across Obsidian hydration dating on the South Coast of Peru, an article by Jelmer Eerkens and colleagues, again soon to be published in the JAS. Eerkens et al. report that obsidian dates are affected by temperature (aha!) and obsidian artifacts at higher elevations hydrate more slowly than those at lower elevations. Since hydration works by measuring the growth of rind, and cold temperatures inhibit that growth, the hydration dates from cold climates would be too young. Eerkens et al. figured out a way to use altitude as a substitute variable for temperature data, something that probably won't work for the Kamchatka Peninsula.

Interesting, though, isn't it? No wonder I can't get anything done.

Sources

• Ushki Lakes
• Obsidian Hydration
• Radiocarbon Dating

Updated 2 Jun 08 to add full citations:

Eerkens, Jelmer W., et al. 2008 Obsidian hydration dating on the South Coast of Peru. Journal of Archaeological Science 35(8):2231-2239.

Kuzmin, Yaroslav V., et al. 2008 Obsidian use at the Ushki Lake complex, Kamchatka Peninsula (Northeastern Siberia): implications for terminal Pleistocene and early Holocene human migrations in Beringia. Journal of Archaeological Science 35(8):2179-2187.