National Geographic : 1958 Aug
I \ through / N /'' \ ( \ , / \ I \\ O% "/ Vegeta . dioxide I" i I"*y <7/; * ** ** ' -~ ~~ C' '' * * "S/"' ' *'*" tion absorbs carbon containing carbon-14. y \\ \\ \\ S\ \\\ \ \\ ural History Museum. This barque formed part of the funeral procession of King Sesos tris (Senusret) III some 3,800 years ago; it was buried near his pyramid at Dahshur, presumably to transport the king's soul across the waters of the nether world (page 237). Dr. Libby's date-3,621 years-was off by only 4T2 percent. Other good results were obtained with cy press wood from the tomb of Egypt's King Snefru; with pine wood from the floor of a large Syro-Hittite palace at Tayinat; and with part of a mummy coffin of the Ptolemaic period in Egypt. "Case of the Counterfeit Coffin" Dr. Libby still chuckles about the "Case of the Counterfeit Coffin," another Egyptian sarcophagus. "It wasn't funny at the time," he recalls. "For one of our tests of the carbon-14 method. we obtained part of the lid of a sarcophagus from one of our best museums. It was sup posed to be about 2,200 years old. "You can imagine our shock when our in struments registered less than a century. This, we thought, was impossible. We checked our equipment and took another reading. Again we got the same answer. "Finally we realized that the instruments Animals feed on vegetation, adding carbon-14 to their bodies. At death 5,568 years Y2 ofcarbon-14 remains 11,136 year V4 ofcarbor remains All living organisms contain the same proportion of carbon-14. After death, organic materials lose their carbon 14 at the same rate. Half disappears in 5,568 years, a half s 16,704 years 70,000 years 1-14 Ye ofcarbon-14 Virtually none remains remains life. Three-fourths dissipates in two half lives, and so on. Radioactivity at any point, compared to radioactivity of modern carbon, tells the amount of time elapsed since death. Drawn by Irvin E. Alleman © N.O.S .