February 16, 1900.] 



SCIENCE. 



273 



they show the possibility of a building up of 

 the earth and the present solar system by the 

 gradual accumulation of small bodies. The 

 investigations by Lunn in connection with the 

 study of the planetesimal hypothesis have 

 shown" that the probable progressive conden- 

 sation of the earth under the influence of 

 gravity is sufficient to account for the heat 

 requirements of past geologic ages as well i as 

 the present high temperature of the interior 

 of the earth. 



It is generally held that the warm and moist 

 climate of the Carboniferous and Tertiary 

 eras was due to an atmosphere much more 

 dense and of much greater extent than the 

 present atmosphere. According to the high 

 authority of Dr. Sv?.nte Arrhenius it is not 

 necessary to make such a supposition. An 

 analysis" of Langley's experiments gave data 

 showing that the competence of carbon dioxide 

 to retain solar heat is so great that its addi- 

 tion to the extent of only one tenth of one 

 per cent, of the present atmosphere would 

 give us a climate like that of the Tertiary 

 era and that the removal of one fiftieth of one 

 per cent, would bring on glaciation-. By later 

 and somewhat more exact experiments of his 

 own Arrhenius'" obtained results indicating 

 that the percentage changes of carbon dioxide 

 would have to be slightly greater than those 

 calculated from Langley's experiments. We 

 must conclude that our present atmosphere, 

 with but very slight variations, would account 

 for the great changes of climate that have 

 occurred in past geologic ages. 



The immense deposits of limestone and 

 coa?^ have been taken to imply a primeval 

 atmosphere containing large amounts of car- 

 bon dioxide. Closer examination" has shown 



"To be published by the Carnegie Institution 

 of Washington. 



"Phil. Mag., S. 5, XLI. (1896), p. 237. 



''^ Ivosmische Physik,' II. (1903), p. 503. 



'^ The coal deposits while large in themselves 

 are insignificant in comparison with the lime- 

 stone. The total coal corresponds to less than 

 four tenths of one per cent, of the carbon con- 

 tained in the limestone. See Dana, ' Manual of 

 Geology,' 4th ed., p. 485. 



" Compare ' The Influence of Great Epochs of 

 Limestone Formation upon the Constitution of 



that it is much more probable that the deposi- 

 tion of limestone and coal has been periodic, 

 as if the atmosphere had been alternately 

 enriched and depleted of carbon dioxide. As 

 a source of carbon dioxide T. Sterry Hunt'" 

 has suggested that it has been received by the 

 earth, from time to time, through the fall or 

 near contact of meteorites, since small amounts 

 of carbon compounds are found in these bodies. 

 The planetesimal hypothesis considers the 

 earth as largely formed from bodies of the 

 general character of the meteorites that reach 

 the earth's surface. Concerning the com- 

 petency of these to furnish the gases of the 

 atmosphere no better can be done than to 

 quote Dr. Chamberlin :" 



Meteorites carry on the average several times 

 their volume of condensed gas; so do many, prob- 

 ably most, igneous rocks of the earth. * * * 

 Atmospheric material is carried into the earth's 

 body by them to-day in quantities that are large 

 rehxtive to their masses. * * '■■ The gases chiefly 

 occluded in meteorites and the crystalline rocks 

 are hydrogen, carbon dioxide and carbon monoxide 

 in leading amounts, and marsh gas and nitrogen 

 in small amounts. The atmospheric material 

 thus condensed within the growing earth could 

 become part of the atmospheric envelope only by 

 extrusion. * * * It may be assumed that the 

 internal gases were given off progressively and fed 

 the atmosphere. 



That the planetesimals were quantitatively 

 sufficient to furnish the gases necessary to 

 supply the earth's water and atmosphere, in- 

 cluding the carbon dioxide which has at dif- 

 ferent stages been taken from the atmosphere, 

 will now be shown. The water and atmos- 

 phere'' at present about the globe are estimated 

 to be about 1/5,000 of the earth's mass.'" If 

 water be considered as formed by the action 

 of hydrogen on ferric oxide, as there is ex- 

 perimental ground for believing provided the 



the Atmosphere,' T. C. Chamberlin, Jour. Geol., 

 VI. (1898), p. 009. 



'^ Loc. cit. 



" Year Book No. 3, Carnegie Institution of 

 Washington, p. 236. 



" The mass of the atmosphere is but 1/200 of 

 that of the water and in the present roygh calcu- 

 lations may be entirely omitted. 



•'Chamberlin, Jour. Geol, V. (1897), p. 673. 



