Nezv Hypothesis of Earth-Origin. — Fairchild. 109 
ontologic evidences bearing on ancient climates need to be re- 
viewed in the light of the new meteorology. 
Ill this connection it should be stated, as an interesting 
matter of history, that the planetesimal hypothesis was devel- 
Qped by professor Chamberlin 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 con- 
stituents. This led to the consideration of the origin of the 
atmosphere, which naturally involved the genesis of the earth 
as well as its fluit envelopes. It is a striking illustration of the 
unity of all earth-science. 
As the writings* of professor Chamberlin have so fully dis- 
cussed 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 carbon dioxide forming 
only one three-thousandths part ; but on account of their ther- 
mal potency and their small proportion of the atmospheric vol- 
ume any variation in their quantity produces disportionally 
large thermal 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 di- 
oxide. Consequently we may regard the carbon dioxide as the 
climate-maker, and the important question is with reference to 
the fact and the cause of its volumetric variation. 
The probable derivation of this gas from the earth's inter- 
ior 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 The gas is withdrawn from 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 decay by carbonation and 
the depletion of the atmospheric carbon dioxide, while re- 
striction of the land areas reduces the consumption and allows 
enrichment of the atmosphere. ]Many other modifying, and 
even opposing, factors exist ; but in the long eras of interaction 
• Articles bv T. C. Chambkklin in the Journal of Geology, Tol. -vi, pp. 609- 
621; Tol. vii, pp. 645-584, 667-686, 752-788. 
