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Holmes and I made a quick trip to the sloth site friday with Dr. Art Bettis, Department of Geoscience, University of Iowa. Our goal was to collect a sand sample for optically stimulated luminescence (OSL) dating. The radiocarbon data from the cores we collected last fall were inconclusive and hint that the sloths may be a lot older than we thought. OSL will give us the answer. Sloth veteran Will Mott drove over from Council Bluffs to operate the bobcat and offer his usual extraordinary assistance.
Quartz sand particles have tiny cracks and imperfections in their crystal structure that trap electrons emitted by radioactive elements in the surrounding sediment. The longer they are buried the more electrons they trap. Sunlight resets the “clock” so keeping the sample dark is essential. Accuracy is about plus or minus 10-15%. Expect a date in a couple of months. . . . Dave