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activity can b« detected. Thus the atomic calendar can go no further back than 25,000 years.
Libby estimated that the cypress wood swamp at Myrtle Beach, N.C., is “more than 20,000 year* old.” Ho said the last ice age in the middle west was 12,000 years ago, rather than 20,600 years as is generally estimated by geologists.
He also said this glacial era apparently was going on at the same time in Ireland, England and Germany. The calendar showed that during a recession of the ice cap in North America, spruce tree&grew in what today is known as the Two Creeks, Wise., forest bed and that when the climate turned colder, the advancing ice mowed down the trees, which today are found under a sheath of rubble.
The scientists measured minute amount of radioactive carbon in 300 pairs of fiber sandals found in a cave in eastern Oregon by L. S. Cressman of the University of Oregon and estimated that the sandals were 10,000 years old.
They studied a fish weir made of stakes found during excavations in Boylston St., Boston, to make the estimate of first human life in the east. They also studied ^ncient charcoal remnants of camp fires in New York State and deer antlers from Kentucky.
In studying the radioactivity, Dr. Libby uses a geiger counter, a delicate instrument that records the tiniest spark of radiation. Tne carbon is extracted from fossils by chemical separation.
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