THE AGE OF THE EARTH AS AN ABODE FITTED FOR LIFE. 233 



be passed by with this mere allusion. It would seem obvious, how- 

 ever, that an earth of heterogeneous constitution, progressively reor- 

 ganizing itself, would give larger possibilities of internal shrinkage, 

 and that this shrinkage must be deep seated as well as superficial. In 

 these two particulars it holds out the hope of furnishing an adequate 

 explanation for the deformation of the earth where the hypothesis of 

 a liquid earth seems thus far to have failed. 



But the essential question here is the possibility of sustained internal 

 temperature. It is urged that the heterogeneous, solid-built earth is 

 superior to the liquid earth in the following particulars: (1) It retains 

 a notable percentage of the original potential energy of the dispersed 

 matter, while in the liquid earth this was converted into sensible heat 

 and lost in prezoic times; (2) it retains the conditions for a slow con- 

 vection of the interior material, bringing interior heat to the surface, 

 a function which was exhausted by the liquid earth in the freer con- 

 vection of its primitive molten state; (3) it retains larger possibilities of 

 molecular rearrangement of the matter and of the formation of new 

 minerals of superior density, whereas the liquid earth permitted this 

 adjustment in the prezoic stages. In short, in at least these three 

 important particulai'S, the slow-built meteoric earth delayed the exer- 

 cise of thermal agencies until the life era, and gradual h" brought them 

 into play when they were serviceable in the prolongation of the life 

 history, whereas the liquid earth exhausted these possibilities at a time 

 of excessive conversion of energy into heat and thus squandered its 

 energies when they were not only of no service to the life histor}' of 

 the earth, but delayed its inauguration until their excesses were spent. 



Let it not be supposed for a moment that 1 claim that the alterna- 

 tive hypothesis of a slow-grown earth is substantiated. It must yet 

 pass the fiery ordeal of radical criticism at all points, but it is the log- 

 ical sequence of the proposition that a swarm of meteorites ]-evolving 

 about the sun in independent individual orbits and having an}' probable 

 form of dispersion would aggregate slowly rather than percipitatelj^. 

 If the astronomers and mathematicians can demonstrate that the aggre- 

 gation must necessarily have been so rapid a"S to crowd the transformed 

 energy of the impacts into a period much too limited to permit the 

 radiation away of the larger part of the heat concurrently, the hypoth- 

 esis will have to be set aside, and we shall be compelled to follow the 

 deductions from the white-hot liquid earth, or find other alternatives. 



But I think I do not err in assuming that mathematical computa- 

 tions, so far as they can approach a solution of the exceedingly complex 

 problem, are at least quite as favorable to a slow as to a rapid aggre- 

 gation. If this be so, the problem of internal temperature must be 

 attacked on the lines of this hypothesis as well as those of the connnon 

 hypothesis before any safe conclusion can be drawn from it respecting 

 the age of the earth. 



