No. 54: Nov-Dec 1987
The currently popular model of the earth has its heat generated by the radioactive decay of uranium and other elements. Some of these decay reactions produce helium -- so-called radiogenic helium. But, as the following excerpt asserts, the amount of helium actually detected is way out of line with the measured heat flow.
"The present rate of mantle heat loss, however, is out of equilibrium with the rate of helium loss -- too large by about a factor of 20. Either radiogenic helium is accumulated in the mantle while heat escapes or current models for the bulk chemistry of Earth are in error and much of the terrestrial heat loss is nonradiogenic."
(Oxburgh, E. Ronald and O'Nions, R. Keith; "Helium Loss, Tectonics and the Terrestrial Heat Budget," Science, 237: 1583, 1987.)
Comment. Such data encourage the thought that a portion of the earth's heat may be generated electrically -- we live on a colossal, spherical, electrical hotplate! Who said science was dull?