80 THE GASES IN ROCKS. 



mantle, the rocks are suboxidized. Yet the earth is surrounded by an 

 oxygenated atmosphere. Since oxygen is not developed in the combustion- 

 tube, and does not appear to exist as a free gas in igneous rocks, it is not 

 likely that this constituent of the atmosphere has come directly as an 

 exudation from the interior of the globe. It is to be sought, rather, in a 

 dissociation or decomposition of compound gases by physical or organic 

 agencies. Originally, enough oxygen was derived from water-vapor, by 

 physical means, to permit the beginning of plant life; after vegetation ap- 

 peared, an abundant source of oxygen was found in the carbon dioxide. 



The average gas content of igneous rocks, as determined by the analyses 

 now made, may be used to test the competence of the rocks to yield the 

 present atmosphere. Taking the average volume of nitrogen per volume 

 of rock to be 0.05, which is probably nearer the truth than the figure 0.09 

 given in table 16 l (owing to leakage of air), it would require the liberation 

 of all the nitrogen in the outermost 70 miles of the earth's crust to produce 

 the nitrogen in the present atmosphere. For an estimate of the amount 

 of igneous rock necessary to yield the carbon dioxide which is now locked 

 up in limestone and coal deposits, we may take Dana's figure of 50 atmo- 

 spheres of this gas, and an average of 2.16 volumes of carbon dioxide per 

 volume of rock. To produce these 50 atmospheres of carbon dioxide, it 

 is found that a thickness of 66 miles of crust would have to be deprived 

 of its carbon dioxide 2 a figure which corresponds fairly well with the 

 estimate for nitrogen. If the water of the rocks be placed at 2.3 per cent, 

 a depth of 70 miles would supply the hydrosphere. 



On the planetesimal hypothesis, gas has been supplied from the interior 

 to the atmosphere ever since an early stage of the earth's growth, prob- 

 ably from the earliest stage at which an atmosphere could be held, which 

 may be placed at the time when the earth's radius was about 2,000 miles. 

 From this it appears that only a small fraction of the full gas-producing 

 possibilities of the rocks of the earth was required to supply the atmo- 

 sphere. The fact that gases are still being given forth through volcanoes, 

 and that the ejected lavas still have gas-producing qualities, makes it clear 

 that all the resources of the interior are not yet exhausted. The working 

 qualities of the planetesimal hypothesis, therefore, do not seem to be found 

 wanting in either past possibilities of supply, present output, or prospective 

 reserve. 



ACKNOWLEDGMENTS. 



In conclusion, I wish to express my special thanks to Dr. Julius Stieglitz 

 for constant advice in the conduct of the chemical researches; to Dr. Oskar 

 Eckstein for much valuable assistance in the laboratory; to Dr. R. A. 

 Millikan for helpful suggestions pertaining to physical principles and the 

 designing of new pieces of apparatus; and to my father, Dr. T. C. Cham- 

 berlin, for proposing the investigation, and for constant sympathy and 

 criticism during the progress of the work. 



1 Ante, p. 28. * The limestones, of course, are not here included. 



