Nr. 6] KVARTÆR-STUDIER I TRONDHJEMSFELTET 47o 



ted for Yife til gjenstand for en temmelig utførlig behandling 

 og kom til det resultat, at whatever may have been the true 

 history of our atmosphere, it seems certain that if sunlight was 

 ready, the earlh was ready, both for vegetable and animal life, 

 if not within a century, at all events within a few hundred 

 centuries after the rockj' consolidation of its surface. But was 

 the sun ready? The well founded dynamical theory of the suns 

 heat, carefully worked out and discussed by Helmholtz, New 

 COME, and myself, says NO if the consoHdation of the earth 

 took place as long ago as fifty million years; the solid earth 

 must in that case have waited twenty or thirt^^ million years 

 for the sun to be anything nearly as warm as he is at present. 

 If the consolidation of the earth was linished twent}^ or twenty- 

 five million years ago the sun was probably ready — though 

 probably not then quite so warm as at present, yet warm enough 

 to support some kind of vegetable and animal life on the earth « 

 (Smithsonian Report for 1897, pag. 356 — 357). Men hertil be 

 merker Chamberlin: »the dealing out of this amount of heat 

 may hypothetically have occupied a period many times the 

 twenty or twenty-five million years poslulaled« (Smithsonian 

 Report for 1899, pag. 240 — ^241); og videre fortsætter han: I 

 again heg to inquire whether there is at present a solid basis for 

 anj^ >sure assumption« with reference to the earth's early thermal 

 conditions, either internat or external, of such a determinate 

 nature as to place any strict limitations upon the duration of 

 life« (L. c. pag. 245). Og ganske nylig har Becker behandlet 

 spørsmaalet ut fra et helt andet synspunkt og sier: If it is 

 granted that the compensation level is an eutectic level, and 

 this seems the only inlelligible theory, the age of an earth heated 

 both by compression and by radioactivity can be computed. 

 Geodesists assert that the compensation level is between 110 

 and 140 kilometers from the surface. The smaller depth would 

 correspond to an age so small as to be unacceptable lo geologists. 

 For a depth of 121 kilometers the age would be 68 X 10^ years 

 and one-seventh of the heat emitted would be due to radioac 

 tivity. For a depth of 140 kilometers the age would be 100X10*^ 

 years and 26 per cent of the heat lost would be ascribable to 

 radioactivity. Greater depths of the compensation level seem 

 incompatible with slight strain beneath that level < (Becker: 

 »Isostasy and Radioactivity « — Bull. Geol. Soc. America, Vol. 

 26, 1915, pag. 203). Og i fuld overensstemmelse hermed uttaler 

 saa Becker videre: Tt has often been asserted that the discovery 

 of radioactivity indefinitely prolongs the probable age of the 

 earth. To me it seems that the determination of the level of 

 compensation limits both the age of the earth and the amount 



