676 T. C. CHAMBERLIN 
cause liquidity, we seem to have an equally facile basis for the 
explanation of molten extravasations. 
It may also be remarked that the acquisition of an atmosphere 
and hydrosphere at a moderate temperature when the growing 
earth reached a medial size introduced conditions congenial to 
life at a stage sufficiently anterior to the Cambrian period to 
satisfy the most strenuous demands of theoretical biology. Most 
of the restrictive arguments of Lord Kelvin and others lose their 
application under this hypothesis. 
Returning to the atmospheric problem, it is to be remarked 
that the assumption of a limited early atmosphere may be enter- 
tained quite apart from the foregoing accretion hypothesis. 
Under the current hypotheses of the separation of the moon, © 
whether by the annular mode of Laplace or the fission mode of 
George Darwin, great rotary speed and high temperature are 
assumed as necessary or probable conditions. We have seen 
that these seem to put the retention of the atmosphere in jeop- 
ardy. The balance of theoretical probabilities, as I now see 
them, favors the presumption that the atmosphere would have 
been greatly reduced under these conditions. There does not 
therefore seem to me any firm ground, even on current theories 
of the earth’s origin, for insisting on the acceptance of the doc- 
trine of a vast primitive atmosphere, as the great reservoir from 
which subsequent abstractions have been chiefly taken. I think 
we are free, therefore, toassume just such a Paleozoic atmosphere 
as the life and deposits of that time seem to imply, interpreted 
by the phenomena of today. Such an interpretation seems to me 
to indicate conditions not radically dissimilar to those of the 
recent geological ages; warm climates in high latitudes at 
times, colder climates in lower latitudes at times, moisture at. 
times, aridity at times, and like oscillations. This view carries 
with it the necessary corollary that the atmosphere has been 
supplied by accessions in some near proportion to its losses. 
That additions have been made to the atmosphere of vital 
importance is a familiar doctrine, but it is here pressed to an 
unfamiliar degree. 
