386 



THE DEEP SEA 



plausible as lo and Pa, even though not isotopes, possess similar 

 chemical properties. In this case, Pa/Io ratio in the sediment is 

 only a function of the age (Fig. 10). The method presents a great 

 advantage in that it would be independent of the concentration of 

 uranium in the ocean with respect to time. 



Pa/Aio 



50 



AO 



30 



20 



50 



200 



250 



100 150 



Time (x 1000 years) 



Fig. 10. Curves 1 and 2 show theoretical growth of protactinium and ionium 

 from initially pure uranium. Curve 3 shows the change in ratio of activities of 

 protactinium and ionium with time (Sackett and Potratz, 1958). 



Methods Based on Growth of Ionium and of Protactinium 



In the event of the uranium being separated from its daughter 

 elements, the ratios of the activities of lo to U-^^ and of Pa to 

 U-^"' would also make possible a measurement of age (Fig. 10). 



This method would be applicable to aragonitic formations, 

 which concentrate uranium at the moment of their formation, but 

 which do not contain ionium. Barnes et al. (1956) applied the 

 method to coral reefs. More recently, Tatsumoto and Goldberg 

 (1959) showed its applicability to oolites. 



Miscellaneous Methods 



Finally, it would be useful to mention, among the methods under 

 study, the argon/potassium and helium/uranium methods, applied 



