Interpretation of heat flow equality

Abstract

It is generally agreed that the approximate equality of the mean rates of heat flow from continents and from ocean floors cannot be an accident. The known composition of continental material indicates that between one-half and three-quarters of the heat that leaves the surface of the continents must be generated by radioactive substances in the continental plates themselves. One would therefore expect the heat flow over continents to be much greater than that measured at the ocean bottoms where the crust is exceedingly thin. Lee [1963] has analyzed data from 73 continental stations and 561 ocean bottom stations; he finds the mean of the oceanic heat flow to be 15% larger than the mean of the continental heat flow. (The flow refers always to unit area.) Since the statistical dispersion of the data is large, not much smaller than their mean, little significance can be attributed to the 15% difference. There remains the question: why is the heat flow from continents not appreciably larger than that from ocean bottoms? The answer that has often been given is that continents were formed by a localized, essentially vertical rising of basaltic material and that there have been no major horizontal movements in the upper mantle. According to this explanation, the net amount of radioactivity per unit area of the earth's surface would be the same everywhere, but under the oceans the radioactivity would be located at a deeper mean level than in the continental regions.