- 33 - natural abundance. Because of the long half life of cl4 (5,600 years) the one per cent increase of cl4 from thermonuclear detonations is an amount that will be detectable in ocean water. | Tritium, H?, is formed in nature by many processes but most often in a manner similar to c14,. Thermonuclear explosions also yield H? as a direct product of the fusion reaction. Since 1952 the total output of bomb-produced He is estimated at 100 pounds, natural H?. than cl4 about five times the amount of ‘Tritium, with a shorter half life (12.5 years) does not travel as far as cl4 before disintegrating but a significant amount is carried from the atmosphere as rain and eventually into the deep oceans before it decays. The addition of bomb-produced H? to the environment has obscured the picture of the natural distribution of H? and increased the amount of H’ in the sea above the values given in Table II. Natural radioisotopes in the sea come from the crust of the earth. More than a dozen long-lived isotopes have been found in our environment but K40 , provide the bulk of natural radiation. me25e | and ye38 Rocks such as granite are more radioactive than limestone or alkaline