National Geographic : 1958 Aug
Iow()ldIsIt? were correct. The coffin lid was modern wood, cleverly antiqued to seem very old. The hoax had fooled the experts and would in all prol)albility have gone undetected except for carbon-14." Perhaps the most convincing test of all was one which matched radiocarbon dating against another type of chronology-that de rived from tree rings. For more than half a century men have rec ognized a connection between the growth of a tree and the rings observable in the cross section of its trunk. During the growing sea son, most trees lay down large, thin-walled cells in the growth layer immediately under the bark. As growth slows, small, thick-walled cells are added; they form a dark ring that marks the end of the year's growth. In many cases it is possible to count these rings and tell how many years ago the tree sprouted. The oldest known living things. the bristlecone pines, show rings going back more than 4,000 years. : * A fine system of tree-ring chronology for archeology in the Southwest was worked out in the 1920's by I)r. A. E. Douglass of the University of Arizona, with the support of the National Geographic Society.t Beams in Spanish missions and Indian pueblos can be dated by matching them against a master pat tern showing closely spaced rings in drought years and broad bands in rainy periods. Sequoia Tests the Carbon Method Dr. Libby chose heartwood from a sequoia nearly 3,000 years old to see if carbon dating would show the same age as the tree rings. This gigantic tree, known as the Centennial Stump, was felled in California in 1874. The fragment for carbon testing spanned rings that grew from 1031 B. C. to 928 B. C. Three tests gave a carbon age averaging about 2,710 years. Although this was some 200 years low, it was still remarkably close. And it amply justified Dr. Libby's conclu sion that "every piece of wood has its age carved in it." The test proved also that the radiocarbon in each year's growth is securely held in chemical combination in the cellulose of that ring, and is not contaminated by carbon from other rings. In 1949 l)r. Libby began dating in earnest, testing the major archeological treasures of the previous 25,000 years. His work, with that of other laboratories which followed, has proved tremendously valuable in recent in vestigations carried out by the National Geo graphic Society at Russell Cave in Alabama,:: at Santa Rosa Island off the coast of ('ali fornia (pages 201 and 266), and in archeo logical sites in Mexico. Not only scientists but even practical minded businessmen find carbon-14 useful. Two oil companies in Texas maintain carbon laboratories to study the age of recent sedi ments. Such knowledge helps in the search for older petroleum deposits. And in the Netherlands, government experts date materials dug along the seashore to find out how rapidly the coast is sinking below sea level. Fortunately the rate is slowing: 7,000 years ago the drop was 14 inches every century: today it is only 4 inches a century. Wood and Bone Reveal Their Age We have been astonished at the variety of materials scientists send to radiocarbon lab oratories. I)r. leyer Rubin, director of the Geological Survey radiocarbon laboratory, showed us such items as a piece of whale baleen, a chunk of wood from King Solomon's mines, and a weathered length of spruce wood once buried by glacier ice in Wisconsin. And neatly tied in plastic bags were numer ous samples of charcoal-the carbon dater's favorite subject--taken from ancient hearths all over the world. One was hearth material from Shanidar Cave in northern Iraq, where recent excavations have gone down 45 feet to reveal several skeletons of Neanderthal men. In other carbon laboratories we have seen the bones of Arizona mammoths killed by early hunters some 12,000 years ago: charred potatoes from the Andes: antlers and walrus hide from Alaska: shells from the Red Sea; salts extracted from South Atlantic waters; mountain sheep dung 11,000 years old from Danger Cave, Utah. I)r. H. R. Crane. of the University of Mich igan laboratory, tells of dating scores of hu man bodies found preserved in the ice near a frozen lake in the high Himalayas. "They turned out to be more than 600 years * See "Bristlecone Pine, Oldest Known Living Thine," ib Edmund Schulman, NATIOxNAl (;GEo(RAI'II(' MA;.\ i'zI :. March, 1958. :'See "Secret of the Southwest Solved by Talkative Tree Rines." by Andrew Ellicott Douglass, NATIONXiA GEOGRAPHIC MA.A .XINI. , December, 1929. ::See, in the NATIOxAL GEO(;RAPHIC MA(i:AzIx:, "Life 8,000 Years Ago Uncovered in an Alabama Cave," October, 1956. and "Russell Cave: New Light on Stone Age Life," March, 1958, both b1 Carl F. Miller.