CHAPTER XXI. 

 CLIMATES OF GEOLOGIC TIME. 



By Chahles Schdchert. 



The ancient philosophers imagined that the earth arose out of darkness and chaos and 

 that its present form and condition came about gradually through the creative acts of an 

 omniscient and omnipotent God. Certain Greek philosophers tell us that the world had 

 its origin in a primeval chaos; others that it arose out of water or an all-pervading primeval 

 substance with inherent power of movement ; that the energy of this primal matter deter- 

 mined heat and cold, and that the stars originated from fire and air. It was Empedocles 

 (492-432 B. c.) who first told us that the ulterior of the earth was hot and composed of 

 molten material, an opinion he formulated after seeing the volcanic activity of the Sicilian 

 Mount Etna, in whose crater he is said to have met his fate. 



The geology of to-day still teaches that the interior of the earth is very hot, but that 

 the material of which it consists is as dense and rigid as steel, and that little of the interior 

 high temperatures attains the earth's surface because of the low conductivity of the rocky 

 and far less dense outer shell. The older geologists believed that this shell originally was 

 thin, and that therefore much heat was radiated into space, this idea being a natural result 

 of the Laplacian theory of earth origin. In other words, they held that the earth was once 

 a very small star which, in the course of the eons, gradually cooled and formed a crust. 

 Therefore it was postulated that, because the crust formerly must have been thin, life 

 began in hot waters and the climates of the geologic past were hot, with dense atmospheres 

 charged with far more carbonic acid and water vapor than they now hold. The present 

 type of climate with zonal belts of decidedly varying temperature and polar ice-caps was 

 thought to be of very recent origin, resultant from a much thickened rocky crust. All 

 of these conceptions are now greatly modified by the planetesimal hypothesis of Professors 

 Chamberlin and Moulton, which teaches of an earth accreting around a primordial cold 

 nucleus through the infaUing of small cold bodies, the planetesimals, all of this material 

 being derived from a spiral nebular mass formed by the colliding of two large bodies. As 

 the nuclear earth grew in dimensions, so also was increased the gravitative pressure, 

 gradually developing central heat which spread to the surface and there broke out in a 

 long period of volcanic activity. 



Our knowledge of glacial cUmates had its origin in the Alps, the land of magnificent 

 scenery and marvelous glaciers, through the work of Andreas Scheuzer, early in the 

 eighteenth century. This was at first only a study of the interesting local glaciers, but out 

 of it gradually came about, especially through the studies of De Saussure, Hugi, Venetz, 

 Charpentier, Schimper, and Louis Agassiz, the appUcation of conditions observed in the 

 .^Ips to the very widely distributed foreign boulders known as erratics and the hetero- 

 geneous accumulations of sands, clays, and boulders called tills. The engineer Venetz in 

 1821 pointed out that the Alpine glaciers had once been of far greater size, and that glaci- 

 ation had been on a scale of enormous magnitude in some former period. By degrees the 

 older conception that the erratics and tills were of flood, river, or iceberg origin gave way 

 to the theory of colder cUmates and glaciers of continental extent. It was shown that 

 the reduced temperature was finally succeeded by greater warmth, and that in the wake 



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