100 YEARS AGO

The utilisation of the internal heat of the earth has often been suggested as an engineering problem of the future. The Rev. E. Rattenbury Hodges directs our attention to an issue of the Boston News Bureau in which a scheme is seriously proposed by the official geologist for Pennsylvania of the U.S. Geological Survey and also by Prof. Hallock, of Columbia University, New York, for drawing on the earth's internal heat by means of deep borings. The idea is to admit cold water into a deep boring and utilise the hot water and high-pressure steam produced. Mr. Hodges points out that he made similar suggestions in the Popular Science News for January, 1894, in an article on “Our Heat Resources of the Future”. He remarked, however, at the time, “The great objection to this drawing on the earth's ancient store of thermal energy would be that her cooling and consequent shrinking would be accelerated; in other words, earthquakes would necessarily become more frequent, and possibly more violent and destructive in their effects.”

From Nature 13 November 1902.

50 YEARS AGO

Temperature of the Interior of the Earth Bullen has derived both the density and the compressibility of the earth as functions of depth, and has found that the bulk modulus k, which is the reciprocal of the compressibility, is a linear function of the pressure p: k = k0 + ap. Ramsey has re-examined this relation from the point of view of the theory of solids, and his conclusions agree with those of Bullen, namely, that the linear relation is valid both in the core and in the mantle below 1,000 km. Ramsey, however, found that the constant k0 had different values in the core and mantle, although the derivative dk/dp = a was sensibly the same... It is now possible to make an estimate of the adiabatic temperature gradient throughout the earth... Taking T at 1,000 km. to be 3,600° K., values of T can be estimated at all greater depths. It is found that the temperature at the boundary of the core and mantle is 4,350° K. and at the centre of the earth is a little greater than 4,800° K. The increase throughout the core is thus only 500°. The results should be of considerable interest to Bullard's theory of the transfer of heat from the core.

From Nature 15 November 1952.