DEEP-SEA RADIUM 113 



background were very useful. Paleontology helped 

 geologists to order the protocols of rocks and distin- 

 guish between different periods of geological evolution. 

 Nevertheless, an exact framework was not found until 

 half a century ago, when it was recognized that radio- 

 active elements, each characterized by its own rate of 

 disintegration, are immutable time-keepers. By using 

 the slow transmutation into lead and helium of the two 

 most long-lived ancestral elements, uranium and 

 thorium, the age of rocks can now be determined. The 

 very oldest among them, in which transmutation has 

 proceeded farthest, have ages up to two billion years. 

 Thanks to this discovery of radioactive time-keepers, 

 definite ages can now be ascribed to many different 

 kinds of rocks. 



Another discovery, made in the first decade of the 

 present century, was the relatively high radium content 

 in abyssal sediments like red clay and radiolarian ooze. 

 Using the ordinary measure of radium content, namely 

 units of the twelfth decimal place or one million- 

 millionth part of the weight, J. Joly of Dubhn found 

 samples of red clay from the "Challenger" collection 

 to hold as many as forty such units. This is nearly fifty 

 times more than the average content of radium in sedi- 

 mentary rocks from the continents. 



The question naturally arose: how does this abyssal 

 radium get down to the deep ocean floor and how can it 

 be utilized for age determinations on different sediment 

 layers? 



