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Show ATOMIC CALENDAR Science Tabs Ice Age Date CHICAGO Dating of man's first known appearance on the North American continent, the epoch oJ the ice age, and hundreds of other significant events in the history oi civilization has been achieved in a master "atomic calendar" prepared pre-pared by the University of Chicago atomic scientist, Dr. William F. Libby. Although the Chicago scientists' dates check in most instances with those estimated by other means, anthropologists and geologists may have to make some significant changes in their present theories, according to Dr. Libby, who ia professor of chemistry in the university's uni-versity's institute of nuclear studies. Radioactive carbon, which Dr. Libby demonstrated in 1947 was created in the upper atmosphere by cosmic rays, is the basis for the dating in the new "atomic calendar." cal-endar." The rays form the radioactive radio-active carbon when they strike the nuclei of nitrogen. Some of the carbon which reached the earth is absorbed through food and water by plants and animals during their lifetime. Radiocarbon Is Inde Since the radioactivity is lost at a constant rate (half of it disappearing disap-pearing in 5,568 years), determination determina-tion of the amount of radiocarbon in organic remains provides an index in-dex to the date. The method is accurate ac-curate to within approximately a hundred years. Because all but a minute amount of radiocarbon is gone after 25,000 years, no object can be dated by the Libby method beyond that span. Thus, ancient cypress wood from a swamp at Myrtle Beach, N. C, could be dated only as being "more than 20,000 years old." Geologists estimate the age of the cypress at approximately 200,000 years. The ice age in the middle west, Dr. Libby reported, was 12,000 years ago, rather than the 20,000 years generally estimated by geologists. The glacial epoch was apparently contemporaneous in Europe, for samples of Ireland, England and Germany agree closely with the Wisconsin dating of the final phase of the ice cap. Some of the evidence from which the appearance of man on the wesi coast was established consisted oi 300 pairs of skillfully woven fiber sandals found in a cave in eastern Oregon. A fish weir made of stakes uncovered three years' ago when excavations were made in Bolystun street, Boston, provided some oi the organic material for humans in the east. The age of revolution in man's development, when he turned from hunting and food available in nature na-ture to agriculture, began at least 7,000 years ago. Uses Geiger Counter Mexico was inhabited at least 7,-000 7,-000 years ago, by people who produced pro-duced crude carving and instruments. instru-ments. To determine the amount of carbon car-bon 14, Dr. Libby's method employs a Geiger-type counter, which is fifty fif-ty times more sensitive than that usually used. Refined methods oi chemical separation are required to obtain the carbon 14, which is tested with the counter, for the amount is lower than could be found in ordinary dirt from a garden or dust from a street. A minimum oi an ounce of the organic material to be dated is required, and several ounces are more satisfactory. |