116 THE OCEAN FLOOR 



This obviously opens a road to radioactive age deter- 

 minations in the deposit, since the two elements will 

 decrease together downward in the sediment with the 

 disintegration of the more long-lived component 

 ionium, i. e. to 50[c in 80,000 years, 25 ^c in 160,000 

 years, etc. 



Two American scientists, C. S. Piggot and William 

 D. Urry, were the first to attempt to utilize the hypothe- 

 sis of ionium precipitation for radioactive age deter- 

 minations in long sediment cores, obtained from ocean 

 depths by means of the Piggot corer.- In a series of 

 papers they very ably discussed the problem of the 

 nonequilibrium system of radioactive elements in 

 deposits, showing how the concentration of radium in 

 the deposit should increase from a low value in the 

 uppermost layer to a near-surface maximum reached 

 after about 10,000 years, when the equilibrium 

 radium: ionium had been attained, and from then on 

 downward present the exponential decline with in- 

 creasing depth (and age) characteristic of ionium dis- 

 integration.^ Their first results appeared very promising 

 by yielding smooth curves of the expected exponential 

 type, but their later results produced more complicated 

 curves. Those the authors explained as due to changes 

 in the rate of sedimentation, notably through a dilution 

 of more radioactive clay components with less active 

 calcareous deposit. 



It is obvious that even under the most favorable 

 conditions of undisturbed sedimentation and ionium 



