The Theory of Geological Thermal Cycles

Abstract

IN a review of the second edition of Prof. J. Joly's “Surface History of the Earth” (NATURE, Feb. 14, p. 227) Prof. A. Holmes makes the rather sweeping statement that the proposed mechanism for the alternating accumulation and discharge of heat seems to be physically unacceptable. He appears to justify this view from Dr. Jeffreys' opinion, who originally based his condemnation of the theory on the fact that there is no periodic solution to the equation giving the heat flow in a solid medium. When, however, change of state occurs in the medium, we have to allow both for the motion of the medium itself and also for the latent heat of fusion, and obviously the original differential equation will have very little bearing on the result. Dr. Jeffreys, in his second edition of “The Earth”, has simply solved this problem by assuming that if at any depth the radioactive materials were sufficient to raise the medium above the melting point, then the resulting convection currents would exactly carry off the excess heat and a steady state would again be attained. Mathematically, this is equivalent to assuming that the effective conductivity of the medium would adjust itself to give the required heat flow at the required temperature gradient. It is not often that Nature is so accommodating.