It would not be proper to make the foregoing interpretation of the cause of geological climates without briefly referring to the various mathematical calculations which have been made by high authorities, and which reach conclusions materially differing from the deductions herein presented.
The arguments of Sir Wm. Thomson[22] and others, to the effect that internal or earth heat could not have affected the climates of the globe, by reason of the non-conductivity of a comparatively slight thickness of crust, are not conclusive. These arguments are based upon:
1. To assume that in a molten or nearly molten planet heat was lost by direct radiation from the heated surface, is to assume a mode of loss that could not possibly occur with the constitution of our planet, nor with one possessing a constitution generally similar.
At the period assumed as the starting point of these calculations the earth’s crust was just forming from the molten state. At this period, which has undoubtedly existed, all uncombined water must have been evaporated, and must have existed as an enshrouding cloud, shutting out solar heat and shutting in earth heat. Our planet at this period must have presented an appearance similar to that now presented by Jupiter, whose available internal heat has evidently not yet been exhausted, and upon whose surface evaporation must be kept up by internal heat.
The loss of internal heat by a globe constituted as our planet, must proceed, not by the radiation and loss of heat directly into space, but by the performance of work in the expansion of water to vapor, the exposure of the upper or cold surface of the partly condensed vapor to loss of heat by radiation into space.
The existence of a non-transcalent cloud shield is geologically recorded in most unmistakable terms, as previously explained, by the maintenance of eras of tropical, temperate and frigid climates from pole to pole—irrespective of latitude; by the glaciation of areas over which solar energy, when not thus shut out, was capable of removing glacial conditions and establishing much warmer climates; also by the contrast of geological climates with solar climates, one independent of, and the other mainly dependent upon, latitude.
Thus the loss of heat by the crust must have proceeded with great slowness; and the crust in thus cooling was, by the laws of cooling solids, made as thick as possible.
2. The non-conductivity of this cooling crust was a cause of the long, instead of a cause of short duration of the internal heat, for when too thick to yield up its heat by conductivity, additional increments were but slowly set free by denudations, faults and fractures. The volume of heat thus set free may be partly grasped when it is considered that no portion of the crust can be reached that is not built up of denuded materials. Heat imprisoned by a non-conducting crust is more certain of liberation by denudation than if the crust were composed of strata having the conductivity of beaten silver.
The assumption that the low conductivity of the crust was a cause of the short duration of earth heat as a controlling factor is exactly contrary to the actual tendency of such low conductivity.
3. From the cold outer surface of the cloud envelop heat would radiate much more slowly than from the more highly heated surface beneath. Indeed, there is every reason to assume that this upper surface may have been partly composed of fine crystals of ice, as cirrus clouds may now be. Upon this upper surface, whatever may have been its condition, was received every thermal unit of heat reaching our globe from exterior sources from its development to the culmination of the Ice Age. What calculation has considered this single factor? which, for aught we know, may have been but little less than the original available store. To what consideration is any discussion which omits this factor entitled?
Having properly assumed a temperature which would necessitate the evaporation of all uncombined water and its suspension above the heated surface, a scientist should follow the results to their legitimate and logical conclusion, and not neglect the existence of a condition necessarily coexistent with those assumed.
The removal of the enshrouding clouds need not be assumed; such removal was blazed upon the globe in broad zones of climate and life which only solar energy could maintain. These lines are as distinctly different from those written by earth heat as daylight is from darkness.
When this removal did take place the fact was graven upon our planet by the melting of the massive glaciers deposited during and before such removal, and by the establishment of the existing conditions.
All calculations and discussions omitting these three factors must reach illogical and erroneous conclusions. The omission of a single one would be fatal, and entitle the result to no farther consideration, and justifies the cynical view that “There is something fascinating about science. One gets such wholesale returns of conjecture out of such trifling investment in facts.”