Show S SCIENCE C I E N. N C ENE NEWS V S OT Helium imprisoned in roc rocks s can be used as asa asa asa a clock to determine their age Its usefulness usefulness use use- in this respect depends on the thc fact that helium is one of the products o of the decomposition decomposition tion of radioactive atoms which break down at known rates so that a given mass of helium in relation to the elements clemen ts still in the rock will have a definite time significance ance Applied to various rocks from deep copper mines the thc helium method has shown them to be from to years old |