CHAMBERLIN— THE AGE OF THE EARTH. 257 



tion in hand. We have no call to discuss the age of the ocean at all 

 unless we are ready to be frank about the other end of its history. 

 The crux of the issue lies there. We are all agreed about the age 

 of this end. 



The Two Types of Assumptions in Actual Use and their Radical 

 Differences }*" — Only two general types of assumptions require recog- 



1* The four estimates of the age of the ocean which were cited earlier 

 and which give an average age of 95,000,000 years, with a range from 70,000,- 

 000 to 150,000,000 years, seem clearly to have been made on the basis of the 

 inherited view of the origin of the earth. This assumes that all the material 

 of the present hydrosphere, together with such substances of the present earth 

 body as would be volatile at the temperature of molten rock, were held in 

 the atmosphere which surrounded the supposed molten earth. The oceanic 

 history is assumed to have begun when the waters from this primitive ocean- 

 bearing atmosphere condensed upon the crust that had formed over the 

 molten earth. The great influence which this view has had on geologic 

 thought and the wide extent to which interpretations derived from it enter 

 into various geologic concepts not recognised as its offspring, are chiefly due 

 to the explicit teachings of the old masters who had clear cosmological con- 

 ceptions and the courage of their convictions. Foremost of these among 

 Americans was Dana, and as I once believed and taught this view but have 

 become an apostate from it and the protagonist of another view, J. trust that 

 in following Dana's statment in the Fourth Edition of his Manual of Geology 

 as a standard exposition I shall not be doing any injustice to the inherited 

 view. 



On the other hand, the only accretional view that has been carried out into 

 any measure of detail is the planetesimal hypothesis. (The most recent state- 

 ment of points pertinent to this discussion may be found in a series of articles 

 entitled " Diatrophism and the Formative Processes," I. to XV., Jour. Geo!., 

 Vols. XXI. (1913) to XXIX. (1921), particularly articles X. to XV.). To 

 clear the air of needless fog let it be noted that this is not a speculation re- 

 garding the origin of the universe, or of the stars, or even of our sun. It is 

 merely an endeavor to explain the singular dynamic properties of the earth 

 and its fellow planets and their strange relations to the sun. It is merely a 

 definite endeavor to solve a very definite problem. It started from an attempt 

 to test the tenability of the inherited view of the atmosphere just outlined. 

 The hypothesis that the atmosphere once held as vapor all the water of the 

 ocean and much other volatile material', was framed before the nature of gases 

 was known. The view seemed logical enough under the old notion of gases. 

 Special reasons for testing it by the kinetic theory of gases arose out of the 

 relations of the atmosphere to glaciation. The results of the test were very 

 unfavorable. It seemed wholly improbable under the kinetic constitution of 

 gases that a molten earth could hold so vast and active an atmosphere. This 

 adverse result led to other tests of a more mechanical sort. These disclosed 

 certain critical facts in the dynamics of the solar system which, while not al- 



