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A “Mammoth” Surprise

As Shannon tells us, in contrast to isotopic methods (such as radiocarbon dating; 14C), which uses a function of elemental decay or buildup, OSL dating measures the growth of natural environmental radiation that results in trapped electron charged signals within a mineral grain that are eliminated by exposure to light or intense heat. Basically the longer a grain is buried from light, the more a signal is preserved on various grains of sediments.
The crew in 2016, included Paul Hanson (University of Nebraska, Lincoln), Liz O’Rourke (USGS), Shannon Mahan (USGS), along with individuals from The Mammoth Site: Justin Wilkins, Monica Bugbee, Dr. Steve Holen, Sandy Swift, and Dr. Jim Mead. Samples of sediments were removed using a number of techniques such as chisel and hammer, electric saw, and core drilling. Background radiation was determined using a portable gamma spectrometer.
Research continued as samples were taken from around Hot Springs and the Black Hills region to help with comparisons for the OSL testing. The analyses in the two labs takes a fair amount of time to make sure that the end results are accurate. The final results just became available. “We were pleasantly surprised!” said Dr. Mead, adding “We just knew that the age had to be more ancient than the 14C 26,000 years old, but the 140,000 is a nice shocker.” The researchers know that at 140,000 years ago the climate of the Earth was heading into an extremely warm interglacial period – “warmer than what we are in today – at this time South Dakota and elsewhere was coming out of a period of massive glaciers covering all of Canada and much of northern-most USA” said Mead. “We are still learning a lot about The Mammoth Site sinkhole and its 60+ mammoths.” “The work this summer should prove to be very rewarding!”
For more information please contact Bethany Cook at or at 605-745-6017.
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