AND ITS INHABITANTS 49 



increased pressures that again found relief in the rising tongues 

 of heated matter. This condition is believed to have continued 

 for a very long time, and to have been particularly active 

 during the last half of the Formative era and the first era of 

 geologic time, an age that may have endured for one-eighth 

 to possibly one-fourth of the earth's entire history. The 

 boiling process not only disseminated the internal heat, but also 

 brought about an irregular sorting out of the heavier and 

 lighter substances, so that the more basic and metalliferous 

 materials as a rule sank to ever lower levels, while the less 

 heavy acidic ones rose as granitic rocks toward the surface of 

 the earth. Finally, at the close of this first era, the Archeo- 

 zoic, the lithosphere or outer rocky and more or less rigid 

 shell may have had a thickness of 50 miles. Through such a 

 rocky mass little of the internal heat rises to the surface, and 

 life would be impossible on the earth if it were not for the 

 constant flow of the sun's radiant warmth, made equable and 

 usable by the atmosphere. These conditions were already 

 present in the Archeozoic era. 



Origin of continents and oceanic basins. It is well known 

 to geodesists and geologists that the continents are built of 

 lighter materials, essentially of granites, while the greater 

 oceanic areas have the heavier basaltic rocks beneath them, 

 and that the difference in specific gravity amounts to about 

 3 per cent. We have seen that these differences came about 

 seemingly as a result of the internal boiling process that pre- 

 vailed during the Formative era and the Archeozoic, and so 

 it appears that the higher continental masses and the depressed 

 oceanic basins came into being very early in the history of 

 the earth. The same interrelation of masses is also to be 

 seen in the moon. 



This is theigneous theory of the origin of oceanic basins 

 and continental jrattonns_pjFJBarrell, and it holds that the 

 differentiation took place after the earth had attained its com- 



