412 CARNEGIE INSTITUTION OF WASHINGTON. 



GEOLOGY. 



Chamberlin, T. C, University of Chicago, Chicago, Illinois. Study of funda- 

 mental problems of geology. (For previous reports see Year Books 

 Nos. 2-19.) 



The principal work of the year has been a study of the phases, 

 relative values, and transformations of energy involved in the process 

 of the earth's self-compression. A comparison made last year^ 

 between the volumes, masses, and densities of the kindred group of 

 planetary bodies consisting of the earth, the moon. Mars, and Venus, 

 disclosed a risiag rate of increase of density with increase of mass. 

 As all four of the bodies compared were formed within a belt covering 

 less than 3 per cent of the radius of the planetary system, it seemed 

 clear that this rising scale of density was a compressional effect. The 

 next important subject to be studied was therefore the process of 

 compression by which this notable effect was attained. There was 

 the more reason for this because recent field studies had been dis- 

 closing new evidences that the deformations of the earth are greater 

 than heretofore recognized. These deformations seemed to imply 

 great stress action, and that in turn implied adequate actuating energy. 

 The most probable source of this was the self-attraction of the earth's 

 own substance acting compressively. 



The question at once arose, what was the previous form or forms 

 of the energy called into action to effect the compression and the 

 deformations that attended it. It was found that the actuating 

 forces came chiefly from potential energies of position and chemico- 

 physical energies. The first arose from the originally scattered con- 

 dition of the planet's material, and the second from such chemical 

 and physical potentialities as could come into action in the course of 

 the compression. 



It seemed advisable to go back to the earth's beginning to see what 

 resources of energy would be available under the different views 

 entertained of the early evolution of the earth. A comparison was 

 therefore made of the potential energies available at representative 

 stages in the two main lines of descent commonly postulated. So 

 far as potential resources of energy available for compressional and 

 distortional action are concerned, practically all genetic hypotheses 

 fall into the one or the other of two classes: (1) those that led to a 

 fluid earth at the time it was first assembled, and (2) those that led to 

 a solid earth at this and even earlier stages, for the critical differences 

 arise mainly from the fluidal and the solid states, respectively. To 

 be definite in the necessarily brief statement here made, it may be 

 understood that the standard gaseo-molten earth of the old masters 

 stands for the fluidal type and the planetesimal earth for the solid 



lYear Book No. 19. for the year 1920, pp. 366-383. 



