National Geographic : 1955 Dec
787 Audrey and Frank Morgan Eskimos in Bering Strait Paddle Hide Boats to Another Hemisphere and Another Day Canopied with fog, Big Diomede Island has stood for ages as a steppingstone between Siberia and Alaska. When Bering's land bridge was submerged, migrants to North America may have steered boats across the strait or walked the ice in winter (opposite). These United States citizens come from Little Diomede Island, a part of North America. Big Diomede, less than three miles distant, is a Soviet possession in Asia. The International Date Line splits the channel between them. When it is Saturday on Little Diomede, it is Sunday on Big Diomede. remainder disappears in another 5,500 years; and so on. After 33,000 years only 1/64 of the original amount is left. Yet even this minute remnant can be measured with spe cially shielded Geiger counters (page 798).* During life, the carbon 14 in humans, ani mals, and plants is constantly disintegrating and being replaced. After death the carbon 14 in the remains continues to disintegrate but is no longer renewed. Consequently, the time that has elapsed since death can be measured by determining how much carbon 14 is still present in proportion to the ordi nary carbon which does not disintegrate. If the carbon 14 has dwindled to half its original ratio to the ordinary carbon in the specimen, the remains are about 5,500 years old; if about one-quarter the original ratio, the relics date from some 11,000 years ago. This dating method works best when used on wood, animal bones charred in cooking fires, on the charcoal of such fires, clothing, plant remains, ashes of funeral offerings buried with a body, shells, and organic matter such as animal dung. Uncharred bones are not satisfactory because they contain an in sufficient amount of carbon. Known Samples Verify Method Accuracy of carbon 14 dating was checked by Dr. Libby and Dr. James Arnold in tests of wood and other matter from Egyptian tombs whose age already was well established by other methods. It also has been tried on a California redwood tree whose age was in dependently known from the number of its growth rings. The results checked. The oldest man-made relics in North Amer ica dated directly by the carbon 14 method * See "Man's New Servant, the Friendly Atom," by F. Barrows Colton, NATIONAL GEOGRAPHIC MAGA ZINE, January, 1954.