STATEMENTBY DR. W. F. LIBBY ON CARBON 14 FROM BOMB TESTS Bombtests to date have produced enough carbon 14 so that when it has come to mixing equilibrium it will have increased the amount naturally present in ali living maiter by one-third of 1 per cent. The normal radiation dose from carbon 14 may be compared with the increase in the dose from cosmic rays as the elevation increases, In these terms the normal carbon 14 dose (1.5 mr/year) is equal to about a 100-foot increase in elevation. Therefore, the extra radiation dose from this product of nuclear tests is equivalent to an increase in altitude of a few inches. In the years before equilibrium with the deep ocean is reached— about 500 years—the level will temporarily rest at about a 3-per cent increase or the equivalent of a 3-foot altitude increase, This is after the first period of perhaps 10 or 20 years before dilution in the top layer of the ocean and with living and dead organic matter occurs, when the increase will be about 20 per cent, or about 20 feet equivalent altitude increase. Because the lifetime of radiocarbon is very long— 8,000 years on the average —the equilibrium situation is the more significant. 268