Friday, June 09, 2006

New study shows much of the world emerged from last Ice Age together
The end of the recurring, 100,000-year glacial cycles is one of the most prominent and readily identifiable features in records of the Earth's recent climate history. Yet one of the most puzzling questions in climate science has been why different parts of the world, most notably Greenland, appear to have warmed at different times and at different rates after the end of the last Ice Age.
However, a new study appearing in the upcoming issue of the journal Science suggests that, except for regions of the North Atlantic, most of the Earth did, in fact, begin warming at the same time roughly 17,500 years ago. In addition, scientists suggest that ice core records from Greenland, which show that average temperatures there did not warm appreciably until about 15,000 years ago, may have remained in a hyper-cold state largely as a result of events triggered by warming elsewhere.

They remark on a dating technique that I hadn't heard of until today and then twice:
The research, led by Joerg Schaefer from the Lamont-Doherty Earth Observatory, a member of The Earth Institute at Columbia University, and George Denton at the University of Maine, relied on a method known as cosmogenic or surface-exposure dating, which enabled the scientists to determine how long rock surfaces have been exposed since the glaciers retreated. As cosmic rays penetrating the Earth's atmosphere strike the scoured rock, they form an isotope of the element beryllium, 10Be, at a known rate. By measuring the minute amounts of 10Be in rock samples from glacial moraines in California and New Zealand and comparing these data to previously published results from Wyoming, Oregon, Montana Argentina, Australia and Switzerland, Schaefer and his colleagues were able to narrow down when glaciers around the world began to retreat.

I'd just read a Science article on the possible cause of the Younger Dryas and whether it was a result of the large glacial Lake Aggasiz in Canada suddenly emptying its fresh water into the north Atlantic and shutting down the thermohaline circulation. Haven't seen it used archaeologically though, but I'm not particularly well-read in the areas it might be of use.

Update: Did a little searching and found at least one paper using it (sub only):

Flint procurement strategies in the Late Lower Palaeolithic recorded by in situ produced cosmogenic 10Be in Tabun and Qesem Caves (Israel) Giovanni Verria, Ran Barkaib, Avi Gopherb, Michael Hassc, Peter W. Kubikd, Michael Paula, Abraham Ronene, Steve Weinerf and Elisabetta Boarettog, Journal of Archaeological Science 32(2) 2005, Pages 207-213

The in situ produced cosmogenic beryllium isotope, 10Be, in flint artifacts from different layers in prehistoric caves can provide information on flint procurement. The buildup of 10Be in a flint matrix is related to the exposure time of the flint to cosmic rays. Although this exposure history can be complex, the 10Be content of flint assemblages can show whether the raw material was obtained from shallow mining and/or surface collection as opposed to sediments two or more meters below the surface. Flint artifact assemblages from two Palaeolithic caves in Israel, Tabun and Qesem, were analyzed.

In Tabun cave the flint artifacts from Lower Layer E (Acheulo-Yabrudian, around 400 000–200 000 yr) contain very small amounts of 10Be, which is consistent with flint procured from sediments two or more meters deep. Artifacts from above and below Tabun Lower Layer E show a more complex distribution, as do artifacts from all layers of Qesem cave (Acheulo-Yabrudian). This is probably due to the fact that they were surface collected and/or mined from shallow (less than 2 m) depths. We show here that artifact assemblages have different concentrations of 10Be, indicating different raw material procurement strategies.

They're only using it to distinguish between mined and surface-collected material, reason being that buried sources would have little 10-Be compared to nodules that had been lying on the surface for a long time. Wonder if this could be used on regular old lithics, much the way that obsidian hydration is used. It seems as though the entire chunk of rock would be affected, not just the surface, so you wouldn't be dating the creation of the fresh surfaces. So, eh.