SECT. 1] 



THE FLOW OF HEAT THROUGH THE FLOOR OF THE OCEAN 



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ocean trenches, since they have not been found in the Japan Trench (Uyeda 

 et ol., 1962), the Puerto Rico Trench (Gerard et al., 1962) or the Aleutian 

 Trench (Foster, 1962). 



Exchiding the high vahies on the ridges and in the Gulf of California, the 

 values give a roughly normal distribution, the means and standard deviations 

 of the values available in late 1960 being : 



Atlantic 1.06 ± 0.055 (^cal/cm2 sec S.D. = 0.25. 

 Pacific 1.09 ± 0.094 pLcal/cm2 sec S.D. = 0.65. 



The means agree closely and it seems probable that their mean, 



1.08 ± 0.054 [acal/cm2 sec, 



represents the mean oceanic heat flow away from the ridges with an uncertainty 

 of 5 or 10%. This is close to the continental mean, which is less well determined 



Fig. 11. Section across the South American trench showing heat flow and generalized 

 topography. 



but probably lies between 1.1 and 1.5 [xcal/cm^ sec. The scatter of the Pacific 

 results is greater than that of those from the Atlantic. This is probably due to 

 the former being drawn from a much wider area. 



To maintain a. heat flow as large as that observed requires very large amounts 

 of heat if it is to be continued through geological time. In 10'^ years the total 

 heat flowing through 1 cm^ amounts to 3 x 10^ cal, which is the heat generated 

 by the complete combustion of a layer of coal 270 m thick. The contribution to 

 the heat flow from chemical and biological processes in the sediments is 

 negligible compared to this, as also is that from radioactivity in the sediments 

 and from compaction. These and other sources of heat have been discussed by 

 Bullard et al. (1956). 



The only adequate source of heat that has been suggested is radioactivity 

 within the earth. The observed heat flow is about that which would be expected 

 from the uranium, thorium and potassium contained in an earth built uj) from 

 stony and iron meteorites. If the earth were in fact built up from meteorites, 

 the radioactivity would initially be distributed uniformly through the mantle. 

 This would lead to melting and probably to an upward migration of the radio- 

 active elements, which tend to be concentrated in the materials crystallizing 



