CHAPTER XXIX 

 ANIMALS OF THE PAST 



Chamberlin* maintains that the earth could not have 

 originated from the gradual condensation of a gaseous 

 nebula, as Laplace believed, but was probably ejected from 

 the sun on account of the attraction exerted by a passing 

 star. He believes that it probably solidified very soon and 

 that it grew somewhat by the accumulation of smaller 

 bodies (planetesmals) on its surface. "The juvenile shap- 

 ing of the earth may be said to have begun as soon as the 

 planetesmals began to plunge into the earth-knot of the 

 nebula; and both knot and planetesmals began to gather into 

 a dense body. The drawing of an atmosphere close about 

 the young earth commenced almost simultaneously. The 

 gathering of the primitive waters into the hollows of the 

 earth-surface soon followed. -These three concurrent activi- 

 ties were master-processes in the growth of the infantile 

 earth; they were the geologic triumvirate. They wrought 

 together toward the earth's final shaping into the litho- 

 sphere, the hydrosphere, and the atmosphere. The con- 

 tact surfaces between earth, air and water are the sites of 

 the most distinctive activities of the present day, and as 

 far back as a good record goes these contact zones have been 

 the seats of the most declared denudations and depositions. 

 They have been almost the sole habitats of biological and 

 psychological activity. From the naturalistic point of 

 view these climatic developments embody three great steps : 

 (1) an ascent in the complexity of physico-chemical combi- 

 nation until it attained the organic type; (2) an evolution 

 of physiological processes and of organs subservient to 

 these; and (3) the initiation and the varied development of 



* "The Origin of the Earth," 1916. 



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