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    Articles by Dave

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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

     fossil hunters til end1sm Art recording GPS coord sm admiring tools 309sm Art Bettis close up 340sm capping tube 328sm Will closeup 312sm Holmes watching 326sm Will Mott 310sm mud flying 303sm Will extracting tube 320sm Art checking depth 294sm Art and Will 297sm Will digging 299sm thanks Evans Rentalsm two more sampling tubes sm site Dec 2011 283sm fossil hunters til end2sm   

     extracting tube 321sm beaver dam 282sm capping tube 358sm Art pounding  tubesm Art driving in tube 315sm Art capping tube 337sm extracting tubes 351sm

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