TRANSACTIONS OF SECTION C. 645 



aa much carbonic acid as the air, but even if this were all available the main- 

 tenance of conditions congenial to life would still be geologically short. Abroad 

 comparison between the atmospheres of the palaeozoic and the cainozoic times fails 

 to give clear proof of radical differences. The magnolia flora in North Greenland 

 in tertiary times indicates scarcely less wide distribution of warm climate than the 

 life of the same region in palreozoic times. The glaciation of India, Australia, and 

 South Africa at the close of the palaeozoic era is even more marvellous thau that nt 

 the close of the more recent era. The salt deposits of middle latitudes, especially 

 of Michigan and New York, imply as great aridity as we find at any time since. 

 The early life does not give clear proof of more carbonic acid in the air than the 

 later life. The tardiness of land life may be accounted for otherwise. 



But the amount of carbonic acid taken from the air by carbon-bearing deposits 

 is estimated variously at 12,000 to 150,000 times that now in the air. At least 

 8,000 or 10,000 times the present amount of carbonic acid has quite certainly 

 beentakeu out since air-breathing life began. This forces the question whether all 

 this carbonic acid, or any major part of it, was ever in the air at any one time. 

 The alternative is to suppose the air to have been fed as well as robbed during 

 all the geological ages. The current view of a former vast, dense, hot and moist 

 atmosphere has, however, been derived more from theories of the earth's origin 

 and primitive state than from computation of the material removed from it. The 

 belief in the gaseous origin of the earth naturally carries with it the doctrine of a 

 primitive hot atmosphere. The belief in a molten condition naturally led also to 

 the view that the ocean was once all in the atmosphere. This does not, however, 

 rigorously follow. Much of the ocean may have been accumulated since, but I 

 venture to question both the primitive molten state and the inferences drawn from 

 it. There is still some ground to doubt the nebular hypothesis, and to entertain 

 some phase of the meteoroidal hypothesis, but even if the nebular theory be 

 followed as far as the separation of the earth-moon ring, a molten state of the 

 earth may not necessarily follow. The vast size, the tenuity and the high tempera- 

 ture of the supposed gaseous ring suggest its speedy cooling to the form of a ring 

 of discrete solid particles like the rings of Saturn. Moreover, a study of the 

 velocity of the gaseous molecules and the limitations of the power of celestial 

 bodies to hold them, makes it extremely doubtful whether such a ring could 

 control its own hot gases. The same line of study even makes it doubtful whether 

 a molten earth could hold to itself a vast vaporous atmosphere such as the ocean 

 would form. The great velocity of the gaseous molecules at the temperature of 

 a molten earth, and the reduction in the influence of gravity by the high centri- 

 fugal force, combine to render the case a somewhat critical one. 



If the matter of the supposed earth-moon ring became cooled to solid particles 

 while in the ring form, or if the earth were formed by the collision of meteoroidal 

 matter, the temperature of the surface of the earth at any given time would depend 

 on the rate and violence of the infall. A cold earth is theoretically as possible as 

 a hot one. Eeasons may be assigned why the temperature was likely to be low. 



A sketch was given of the hypothetical growth of the earth by the ingathering 

 of the solid particles of the supposed earth-moon ring, in the course of which it 

 was shown that the peculiar constitution of such a body, when it reached the size 

 of the moon, would be favourable to explosive eruptions and liable to give rise to 

 craters like those of the moon. The internal heat necessary would come from the 

 self-condensation of the growing globe. Computations were cited to show that 

 this was adequate. The gases and vapours involved were attributed to atmospheric 

 material carried in by the ingathering particles. When the mass reached a size 

 large enough to hold an atmosphere, this size being probably about that of ]\Ier- 

 cury, or a little larger, it would pick up atmosphere from without and would hold 

 the gases and vapours emanating from within, and thus the atmosphere as an 

 envelope would begin. As soon as it acquired sufficient extent to retain the heat 

 of the sun, the modern phase of the history of the earth woidd begin, and in time 

 the conditions for the presence of life would be reached. This makes the intro- 

 duction of life possible at a very much earlier stage than the current hypotheses, and 

 gives ample time for the most strenuous demands of theoretical biology. The 



