566 R. Tt. CHAMBERLIN 
that the greater the degree of heat the more quickly and completely 
the gases are given off. There is reason to believe that this principle 
applies to the molten state as well as to the solid condition. If it be 
applicable to liquid lavas, it would favor the belief that a molten globe 
would have boiled out most of its gaseous matter before solidifying. 
Gases near the surface should escape rapidly. It might, perhaps, on 
first thought, be held that, while much of the gas in the outer portion 
would be lost, that existing in the central part of the sphere would be 
retained and slowly recharge the peripheral portion after a crust had 
formed and prevented further escape; but the molten globe, by 
hypothesis, grew up gradually, and essentially every part was once 
superficial. Even today, in an essentially solid earth, there are move- 
ments of lava that bring up gases from unknown depths, and it is 
reasonable to suppose that the molten sphere was stirred up by still 
more effective convection currents which facilitated the expulsion of 
gases and vapors, and that almost all of the gaseous material of the 
globe would have been boiled out before solidification set in. 
The complete validity of this view depends much upon the fate 
of the gases after they have reached the surface. It they were retained 
in the form of a dense atmosphere, a condition of pressure-equilibrium 
might be established between the atmosphere and the gases in the 
liquid earth, by means of which the latter would retain some appreci- 
able amount of gas. But if, as some believe, our atmosphere is about 
all that the earth can control," the gas expelled from the molten sphere 
in excess of the mass of the present atmosphere would escape and be 
lost to the planet. Geological evidences—early Cambrian glaciation, 
Paleozoic periods of aridity, and the general testimony of life—all 
point toward the conclusion that early terrestrial atmospheric condi- 
tions were not radically different from those of today. Hf the hypoth- 
esis of a heavy atmosphere be not permissible, it becomes very diffi- 
cult to explain the presence of original gases and gas-producing 
compounds in plutonic rocks on the basis of the Laplacian or other 
hypotheses that postulate original fluidity. 
RELATIVE TO THE PLANETESIMAL HYPOTHESIS 
After the gaseous matter of the ancestral sun was shot out from 
the solar surface to form the two arms of the spiral nebula, as postu- 
«R. H. McKee, Science, Vol. XXIII (1906), pp. 271-74. 
