256 H. L. FAIRCHILD — GEOLOGY UNDER PLANETESIMAL HYPOTHESIS 



evidence bearing on ancient climates need to be reviewed in the light of 

 the new meteorology. 



In this connection it should be stated, as an interesting matter of his- 

 tory, that the planetesimal hypothesis was developed by Professor Cham- 

 berlin as an outgrowth of his studies in glaciology. He found the best 

 explanation of Pleistocene cold to lie in the quantitative variation of 

 the atmospheric constituents. This led to the consideration of the origin 

 of the atmosphere, which naturally involved the genesis of the earth as 

 well as its fluid envelopes. It is a striking illustration of the unity of 



« 



all earth science. 



As the writings* of Professor Chamberlin have so fully discussed this 

 subject the present writing will give only the brief statement necessary 

 to the purpose of this paper. 



Oxygen and nitrogen are transparent to " dark heat," while carbon 

 dioxide and water vapor intercept and store it. The thermal properties 

 of the atmosphere are chiefly due to this property of these two gases, 

 which are least in quantity of the important constituents of the air, the car- 

 bon dioxide forming only one-three-thousandth part; but on account of 

 their thermal potency and their small proportion of. the atmospheric vol- 

 ume any variation in their quantity produces disproportionally large ther- 

 mal effects. The amount of water vapor depends directly on temperature, 

 so that this gas intensifies the effect, either way, produced by changes in 

 the amount of carbon dioxide. Consequently we may regard the carbon 

 dioxide as the climate maker, and the important question is with refer- 

 ence to the fact and the cause of its volumetric variation. 



The probable derivation of this gas from the earth's interior has 

 already been shown, and it may be assumed that the rate of supply is 

 fairly uniform. The gas is withdrawn from the air by rock decay and 

 organic accumulations and is stored in rock strata and the sea. It 

 would seem that the consumption of the gas could not be so uniform as 

 the supply. Broad land areas of crystalline rocks favor rock deca}^ by 

 carbonation and the depletion of the atmospheric carbon dioxide, while 

 restriction of the land areas reduces the consumption and allows enrich- 

 ment of the atmosphere. Many other modifying, and even opposing, 

 factors exist, but in the long eras of interaction between atmosphere, 

 rocks, and ocean there must have been established a fair compensating 

 adjustment between removal and supply of the carbon dioxide, though 

 not an exact balance. Any enrichment of the air in this gas gives the 

 atmospheric blanket greater power to retain the sun heat and produces 

 warmer and more uniform climate, with greater moisture. Depletion 



♦Articles by T. C Chamberlin in the Journal of Geology, vol. 6, pp. G09 62'. ; vol. 7, pp. 545-584, 

 CU7-685, 752-788. 



