384 THE DEEP SEA 







# 



4 I 



20JUL 



Fig. 9. Photomicrograph of pelagic clay particles embedded in a nuclear 

 photographic emulsion. An active microcrystal of barite (?) (Picciotto and 

 Arrhenius, unpublished). 



Methods Based on the Decay of Cosmogenic Radionuclide 



All these methods are based on the assumption that the flux of 

 cosmic radiation remains constant with respect to time. 



Carbon-14. The carbon-14 method is applicable to the car- 

 bonates of the calcareous shells of the planktonic organisms which 

 constitute chalk oozes. Since the earliest observations carried out 

 on Pacific chalk oozes by Arrhenius et al. (1951), a large number 

 of important subsequent results have been published. This method 

 is, at present, still the most reliable one, but unfortunately, is 

 applicable only to intervals of time of the order of 25,000 years. 



Beryllium- 10. This element, for the moment, carries all our 

 hopes for its use to date events between 500,000 and 10 million 

 years. The development of this method is still rather unclear, but 

 excellent reviews are to be found in the articles of IMerrill et al. 

 (1958) and of Peters (1957). 



