DIASTROPHISM AND THE FORMATIVE PROCESSES 



XI. SELECTIVE SEGREGATION OF MATERIAL IN THE FORMA- 

 TION OF THE EARTH AND ITS NEIGHBORS 



T. C. CHAMBERLIN 



University of Chicago 



In the last number of this Journal^ I endeavored to deduce from 

 a comparison of the earth with Mars, Venus, and the moon, the 

 order of magnitude of the total shrinkage suffered by the earth. 

 The results proved surprisingly large. Not only that but they 

 seemed to show that the shrinkage per unit of mass-increase be- 

 came greater as the total mass grew. Since small bodies have 

 but feeble gravitative abiHty to gather and hold the lighter order 

 of molecules in a free state, it seemed probable that the moon and 

 Mars contain higher proportion of the heavy molecules than 

 Venus and the earth. This seemed to add emphasis to the high 

 densities of Venus and the earth compared with the moon and 

 Mars. It appeared to strengthen the presumption that, in this 

 group of bodies at least, the degree of density was due to the 

 concentrating effect of superior mass rather than original heaviness 

 of material. 



However, final conclusions were held in abeyance until the modes 

 of organization of the four bodies could be studied with a view to 

 detecting the probable laws of their segregation in so far as these 

 affect the proportions of inherently light and inherently heavy 

 materials. It is this inquiry that forms the theme of the present 

 paper. 



The subject necessarily reaches back to the genesis of this 

 group of bodies, and the discussion will need to concern itself 

 quite as much with the dynamic environment that influenced 

 their formation as with the material that entered into it. The 



' "The Order of Magnitude of the Shrinkage of the Earth Deduced from a Com- 

 parison with Mars, Venus, and the Moon," Jour, of GeoL, XXVIII (1920), pp. 1-17 



126 



