The dawn of the Archæan Era found the earth a heated globe emerging from an unrecorded and unfathomable era of greater heat. The crystalline character of the earliest rocks demonstrates the high temperature which prevailed upon the surface at that time. Such being the temperature of the surface, it is beyond question that the existence of uncombined water upon it was an impossibility, and as vapor it could only shroud the earth in dense clouds. The earth heat was as effectually shut in from loss by radiation as was solar heat shut out from reaching the surface.
As this finite amount of earth heat could only escape by doing work in the expanding of water to vapor, vast eras of time must elapse before the work done could exhaust the available heat. The process of exhaustion was further retarded by two causes: 1st, the heating of the outer layers of the atmosphere by solar heat; and 2d, the low conductivity of the strata of the earth itself; consequently the climates of the earth, until the final exhaustion of earth heat, being controlled by a uniformly distributed supply, were of remarkable uniformity. The denudations, faults and fractures of its crust set free additional increments of heat but slowly, so that the torrid, tropical and temperate eras were longer than the frigid era.
During the existence of sensible quantities of earth heat the oceans must have been heated from the bottom, and cooled at the surface by evaporation. The evaporation from the total ocean surface under such conditions would give rise to much more extensive cloud formations than at present. Indeed, the record of temperatures and character of life are such as to warrant—nay, even force—the conclusion that the whole earth was one vast hothouse, from which solar heat was shut out, and throughout which a uniform temperature was prevalent from pole to pole.
Solar heat does not penetrate the thinnest cloud; even a fog through which the form of the sun is distinctly visible shuts out nearly all direct solar heat.[15] The failure in the past to recognize the climatic influence which the factor earth heat was able to produce, and the endeavor to ascribe to solar energy the climatic conditions existing during the activity of earth heat, has caused all the mystery and error of attempts to explain the climatic phenomena prior to and during the Ice Age.
Once realize the peculiar influence and domination of earth heat, and these mysteries and errors fade, and the whole system of pre-glacial and glacial climates becomes simple.
The function of solar heat during the activity of earth heat could be none other than conservative of the latter; such function it is now performing for the great planets, Jupiter and Saturn, and probably Uranus and Neptune, whose surfaces are shrouded from our view by clouds.[16]
It would be impossible, in the limits to which it is necessary to restrict this paper, to review the vast array of facts which could be brought forward to demonstrate the perfectly uniform, torrid character of the climates of the globe during the Palæozoic Era.
From the 81st degree of north latitude through every range of present climates to the confines of the south frigid zone, the life systems attest the stifling hothouse character of the climate. The species of plant life and animal life, whether of land or marine forms, varied less from the torrid to the frigid zones than corresponding species upon different continents in the same zone do now. Nowhere below the Permian deposits can fossil life be recognized that does not belong to an ultra-tropical type. Such uniformity of temperature is impossible under solar control, and hence can only belong to a climate controlled by earth heat.
In reviewing the temperatures recorded by the fossil life of the Palæozoic Era, the fact becomes apparent that nowhere upon the surface of the globe during that era were there any zones of temperature. The whole surface was subjected to one universal torrid climate—the life developed was uniform in its general character from the Arctic to the Antarctic circle. Under no possible conditions could such uniformity of climate have been established and controlled by solar heat alone. Hence during this period earth heat was the controlling source.
This era merged gradually into the Mesozoic era of tropical heat, during which the forms of life developed into higher types, and their range of distribution demonstrates the still perfect uniformity of climate. One peculiar and significant fact is recognizable in comparing the land forms with the marine forms of life. The former developed types more suitable to tropical climates, while the latter held more tenaciously to the torrid types, thus proving the more rapid loss of heat by the continents.
The fossil life of the Cenozoic era corroborates to a remarkable degree the still perfect uniformity of climate. Throughout Greenland, Iceland, Lapland and Spitzbergen, as well as throughout present temperate and tropical zones, a perfectly uniform and temperate climate existed. The flora and fauna of the lower Mississippi valley flourished in those localities in which, during the Palæozoic era, only gigantic Ferns, Lycopods, Calamites and corresponding plant and animal life could be found, and where now only a stunted Arctic life can exist.
The palæontological evidence of the Mesozoic and Cenozoic eras is equally convincing as to the perfectly uniform tropical climate of the one and temperate and later frigid climates of the other.
During the latter part of the Tertiary and early Quaternary periods identical types of life existed in all parts of Europe, Asia and America and a uniformly temperate climate prevailed over the whole northern hemisphere entirely at variance with the extreme range of temperatures now embraced in that half of the globe.
The control of the waning earth heat was simply dying out, and had reached that stage in which it was no longer able to maintain the high temperatures of previous eras.[17]
The evidence that the high specific heat of water held the last available remnant of earth heat, and thus perpetuated its control of climates, is beyond dispute, as presented by the conditions culminating in the Ice Age.
Whatever may be the doubts as to the actual date of the Ice Age, there is no disputing the fact that the evidences establishing the culmination of that Age are found above or since the Tertiary, and below or before the Modern Era.
Between these two periods there is abundant evidence from every climate, from every zone of present life, that the continents were glaciated.
Europe and Asia, North and South America, Africa and Australia,[18] all present glacial striæ, boulder deposits, and other marked evidences of glaciation at the same period, just antedating the Modern Era, or during the Quaternary period.
When we examine the evidence found in one of the present climatic zones, this change of climate from an ultra-torrid successively to a torrid, tropical, temperate, and, lastly frigid character, is not only very marked, but is everywhere the same.
Upon the establishment of solar heat in the control of surface temperatures, we find the isotherms entirely at variance with those antedating the Ice Age. We find also strong corroboration in the lines of retreat of the continental ice caps. These lines are sensibly parallel with the isotherms established by solar heat, proving that solar heat was the cause of the disappearance of glacial conditions.
These facts distinctly prove the totally different source and distribution of heat before and since the Ice Age, and that upon the inauguration of climates controlled by solar energy, an obliteration of the conditions left upon the dying out of earth heat set in. Along that zone most exposed to solar energy conditions and life corresponding to the tropical conditions of Cenozoic times have been established; along those zones moderately exposed to solar energy the newly established conditions are analogous to the universally temperate climate of the latter Tertiary and early Quaternary periods; whilst in those zones least exposed to solar energy a removal of glacial conditions is yet in progress.[19]
Wherever fossil life has been developed the order of climates, as thus recorded has been: First, torrid; second, tropical; third, temperate; fourth, frigid; and fifth, the life appropriate to the zone of solar climate—irrespective of that existing previous to the Ice Age. The same order is true for any portion of either temperate zone; under the equator the order of climates has been the same, except a return to tropical conditions and life.[20]
In the North frigid zone this same order of climates has been found, except that there has been no change from the conditions left upon the dying out of earth heat; in other words, solar energy has not removed glacial cold in those regions least exposed to its action.
The removal of glacial conditions has been less in the Antarctic than in the Arctic regions, partly from causes pointed out by Maury, and more fully treated by Dr. Croll. This removal has also been subjected to variations due to the mild astronomical influences ascribed by Adhémar, Croll, Ball, Drayson and others, as sufficient to produce glaciation.
These astronomical causes undoubtedly must have produced slight secular variations in the relative exposures of the two hemispheres to solar heat—but they have not been demonstrated to be of sufficient influence to produce glaciation, and in no way could they sensibly affect climates prior to the establishment of the control of solar heat. (See page 41.)
The distribution of heat, prior to the Ice Age, as recorded by fossil life, being entirely at variance with that now found, and being entirely independent of proximity to, or distance from, the equator, distinctly proves that climates were established and maintained independently of solar heat, and hence belong to the only other source, viz., earth heat.
It is also evident that under no possible conditions could solar energy maintain a torrid, tropical, temperate and lastly glacial climate over the whole range of the present zones of climates, and that this uniform distribution of heat prior to and during the glaciation of the globe was due to an evenly distributed supply from a constantly and uniformly decreasing source.
Moreover, the wide distribution of glaciation over the present temperate and torrid zones is a distinct proof of the exclusion of solar heat from these regions during glaciation. Under no possible circumstances could temperate North America, Europe and Asia and tropical South America have been glaciated unless these regions were shut out during glaciation from that solar energy, which when admitted has removed glacial conditions.
Glacial dispersion followed one of two general laws: First, the great centers or belts from which dispersion took place in apparent disregard of the slope of the ground were areas most exposed to cyclonic activity and resulting precipitation. Second, minor centers of dispersion (or local glacial dispersion) were elevated lands, subjected to uniform precipitation.[21]
Since glacial conditions in the northern hemisphere were removed from southerly towards northerly latitudes, the gradients were increased southerly and decreased northerly from lines of maximum glaciation. Glacial transportation was likewise modified. The reverse of these directions prevailed in the southern hemisphere.
Glaciated areas have been partly relieved of their loads of ice at rates and times proportional to solar exposure, and upon lines parallel with present mean annual isotherms. Wherever remnants of the continental ice sheets of the Ice Age yet rest, this retreat is still in progress from the same cause.
The ascription of great elevations above sea level during the Ice Age is natural, and such apparent greater elevation is due to two causes during this period, whilst due to only one cause during previous eras. As the surface of the earth became subjected to a temperature of 31° Far. under the oceans, and a corresponding temperature under the continental ice caps, contraction and consequent elevation were continued as before; and as snow was piled up upon the continents, water was withdrawn from the oceans; for each million square miles of continental ice cap three hundred feet thick a corresponding three million square miles of ocean was lowered one hundred feet. The continental ice caps already approximately known were too vast not to have lowered the sea level to a marked degree.
The apparent general depression after the Ice Age is as natural. By the melting of the greater portion of the ice caps, and the evaporation of vast inland seas, the sea was approximately restored to the level existing prior to the Ice Age, thus causing an apparent sinking of the land.
The great difference between climatic conditions prior to and since the Ice Age is very marked around inland seas and basins without drainage. Lake Bonneville and Lake Lahontan, in the United States, and the greater area once occupied by the Caspian and other seas, evidence the superior dampness and rainfall antedating the Ice Age. During the control of earth heat the oceans were heated to their bottoms, and furnished moisture enough to keep these great depressions full of water and to support a dense life upon now desert areas. The dry air of the modern era has not only absorbed the water in these vast lakes, and restored it to the oceans, but vaster areas have been converted into deserts by the unequal distribution of heat and moisture under solar control.