The General Proposition.[8]
GIVEN.—A heated globe, constituted and circumstanced as the earth, and whose surface temperatures, by reason of internal heat, are above the boiling point of water, to prove that before its surface temperatures can pass under the control of the solar heat (1) that climatic changes must be independent of latitude, and (2) that the continental areas[9] must be glaciated.
It will be observed that the surface temperatures of a globe thus situated are entirely controlled by its own internal or earth heat; for between such surface and any external source, a dense cloud of vapor must exist. The fact that direct or radiant heat rays cannot pass through dense fogs and clouds is well known;[10] therefore, a globe thus situated can neither give off, nor receive radiant heat. The peculiar function of solar heat during the existence of appreciable quantities of earth heat was to warm the upper regions of the atmosphere and the outer surface of the clouds exposed to its power, thus partly replacing the heat lost by radiation into space, and causing the store of earth heat to last longer.
By the conditions of the problem presented, we thus have a globe having resident in its mass a finite quantity of heat exposed to loss only by means of the gradual expansion of water into vapor, and the exposure of this vapor to loss of heat by radiation from its upper surface into space. This vapor would then condense, and as rain, snow or hail, descend all, or part of the way to the earth, receive another increment of heat, and ascend as before. A slow process, but exhaustive in time.
Thus the property of water to assume three forms, each of which possesses remarkable qualities with regard to heat and cold, afforded the only means for exhausting the earth heat. As vapor, it possesses the property of storing more heat than any other known substance;[11] as snow or ice it possesses the property of storing more cold than any other known substance. The function of solar heat, until the exhaustion of earth heat by this process, was simply conservative; it merely warmed the upper layers of the atmosphere, through whose dense vapor its heat rays could not pass. Clouds being more translucent than transcalent, light rays reached the planetary surface prior to heat rays.
The earth may thus be regarded as having been surrounded by a series of spheroidal isothermal shells of mean temperatures. The one next the surface represented a mean temperature of 212° + t° Far.; t being positive, and proportioned to the greater pressure of the heavier atmosphere existing. Above this isothermal shell were others representing mean temperatures of 90°, 60°, 32°, Zero, etc., to -x° Far., the extreme cold of interplanetary space. Between the two spheroidal isotherms of 32° and -x° Far., was one which had a mean temperature of 32° - y°, and equally exposed to both sources of heat.
That the spheroidal isotherm of 32° Far. was within the sphere of influence of earth heat, is proven by the formation of snow or ice at that temperature, both being the resultant of vapor expanded and raised by earth heat to that height as a minimum. Moreover, vapor would have reached that height as a minimum were solar and stellar heat suspended for a definite period, and the earth absolutely exposed to loss by radiation with no partial return of heat, from exterior sources.
It therefore follows that the isotherm equally heated by both exterior and interior sources was colder than 32° Far. or below that temperature at which snow and ice form. (It is well known that solar energy cannot maintain a temperature as high as 32° Far. except in the lower regions of the atmosphere.)
The isothermal shells nearest the earth were spheroidal in shape, and by reason of the conditions their surfaces were practically parallel with that of the earth; those most remote from the earth, by reason of solar influences, protruded at the equator and flattened at the poles, so as to be slightly more oblate than the earth; they were sensibly parallel with the spheroidal isotherm now marked by the “snow line.” Hence at the equator the direct action of the sun was first felt and established.
As the earth heat was a finite quantity exposed to loss, it was in time exhausted. As this loss proceeded, these spheroidal isothermal shells of mean temperatures shrunk in upon the earth, and their contact with its surface marked the zones of corresponding climates prevailing during the dual source of heat. Since these isotherms were independent of equatorial or polar exposure to solar energy their contacts with the planetary surface established climates independent of equatorial or polar position, or in other words of latitude; and not until those, whose distance from the surface mainly depended upon solar energy, shrunk to the surface could climates ranged in latitudinal zones be established. As the climates established by the contact of the isotherms inside of 32° - y° Far. were independent of direct solar heat, they varied from the climates established by solar heat alone; hence the marked difference between climates antedating and succeeding the Ice Age. The isotherms preceding this age were dependent almost entirely upon elevation above sea level, fractures and conductivity of the earth’s crust; those succeeding it are dependent upon proximity to the equator, elevation above sea level, and the distribution of heat by ocean currents.
At the expiration of a period of time T., the earth lost sufficient heat to cause the isothermal shell of 90° Far. to shrink to the surface except at fractures, and a particularly uniform, moist, and highly torrid climate was established, and types of life developed, culminating in the Carboniferous Age.
The crust cooled sufficiently to permit the demarkation of the continental areas, but the cooling did not proceed to that point which upheaved the massive mountain ranges, nor greatly depressed the ocean areas. Therefore, an era of low, flat continents, and shallow hot seas followed. The life of that period abundantly shows this condition from one pole to the other, and the prevailing temperature is distinctly recorded in the fossil life of the Palæozoic and Mesozoic Eras.
Light rays reached the surface prior to this time, as evidenced by the development of visual organs in animal life.
The greater part of the vapors and gases existing previously in the atmosphere were condensed, and existed upon the surface; the vapors as highly heated oceans, and the gases in various combinations of the mineral and life kingdoms. Now, in the oceans thus formed and further enlarged, there was stored up a vast quantity of the original earth heat, by reason of the high specific heat of water, from which it was not exhausted until the last moment; and in this process of exhaustion, it must have maintained the cloud shield, shutting out solar heat until this the last remnant of effective earth heat was exhausted. Not only this, the oceans thus formed had a mean temperature of 90° + z° Far., z being a positive increment due to the heat received from the bottoms and sides of the ocean. Not until the bottoms of the oceans were subjected to a degree of cold approximating that to which the continental areas were exposed could the crust be cooled uniformly and reach that degree of uniform thickness and stability suitable to the safety and comfort of the human race.[12]
At the expiration of the period of time, T′, the spheroidal isothermal shell having a mean temperature of 60° Far., similarly shrunk to the surface of the earth, and a corresponding uniformly temperate climate was established.
The further cooling of the crust caused its shrinkage, and a consequent greater upheaval of those areas most exposed to loss of heat, the continents. This further shrinkage caused the strata formed during the previous eras to be upheaved and fractured, and the lines of demarkation between oceans and continents were thus more strongly accentuated.
The life developed in the interim evidences an approach to that of the present temperate zones, and its wide distribution demonstrates the complete control of the climates of the globe by internal heat. The isothermal lines were entirely at variance with those established by solar heat, therefore the functions of solar heat remained conservative of those operating on the surface during this period also.
The extreme and uniform distribution of fur or hair-covered animals and of the deciduous and coniferous trees of the Cenozoic era mark further the control of a source of heat more uniformly distributed than solar heat could possibly be. For reasons previously given, this isotherm also reached continental areas earlier than ocean areas. When the mean temperature of the land was 60° the tepid oceans must have had a mean temperature of 60° + y° Far., y, like z, being positive, and due to increments of earth heat received from the bottom.
At the expiration of this period T′, or at some time, T′ ± a, the isothermal shell of 32° Far. shrunk so as to reach the more elevated portions of the continental areas, and thus established a snow line independent of the influences now establishing and maintaining such snow line. The resulting glaciation was controlled by the same general laws that now exist, only the distribution of heat being independent of latitude, and mainly dependent upon altitude above sea level, glaciation of present tropical and temperate latitudes was as certain to occur as in polar regions. The moment a snowflake reached the earth which the waning earth heat was unable to melt, the Ice Age was inaugurated; and the conditions were such as to favor its extension until the exhaustion of the store of heat beneath the oceans and resident in them, by reason of the high specific heat of water. It will be noted here that whenever, in obedience to the expansive force of this waning earth heat, a particle of water was vaporized and made the last round of its circulation, it returned to the earth in that form which stored the maximum degree of cold, or, in other words, in that form which required the maximum amount of solar heat to change.
From the moment that snow began to accumulate, every remaining vestige of earth heat was available for producing those conditions favorable to glaciation, namely, warm seas, dense fogs and cold continental areas; and every unit of solar energy reaching the upper regions of the atmosphere was available for maintaining those favorable conditions.[13] Glaciation under these conditions would be cumulative until the oceans, exhausted of their heat and lessened in area, were no longer able to supply the moisture necessary to completely shroud the earth from direct solar heat.
At the expiration of the time T″, the isothermal shell, having a mean temperature of 32° Far., shrunk in upon the globe, and the oceans were exhausted of their store of heat and their bottoms brought in contact with water having a mean temperature of 31° Far., a temperature approximating that of the ocean depths at present, and of ice in masses.
The isothermal shell 32° Far. was a spheroid circumscribing the earth. In shrinking to the earth its intersections with the surface were controlled by the elevation of the surface above sea level, and by the local escape of earth heat; elevated equatorial or temperate areas were therefore as much exposed to glaciation as polar lands. (For maximum depth of glaciation see page 32.) By reason of the high specific heat of water, this isotherm also reached continental areas prior to reaching ocean areas.
The crust beneath the ocean, having been protected from loss of heat by the superincumbent water, shrunk to its final shape subsequent to that portion forming continental areas. The ocean bottoms in thus shrinking approximately to their present shape must have been fractured, as continental areas had previously been. In this way very considerable increments of earth heat were set free after glaciation had commenced. This process, which is entirely in consonance with known laws, would result in increasing the depth of glaciation, or even in re-establishing it after partial recedence.
There would also result a complicated series of crust movements as the continents were relieved of pressure by the melting of the ice caps, and the ocean bottoms subjected to increased pressure by the restoration of water to the oceans.[14]
Thus the same forces which, even before the eras we have been considering, must have built up upon the surface of the globe mineral forms of surpassing beauty, only to be destroyed and ground down to give place to vegetable and animal forms of wonderful development—these same forces were called upon to well nigh obliterate every living individual of both kingdoms. The efficiency of their work is attested in every zone of life from the equator to the poles.
The exhaustion of the residuum of earth heat in the oceans and beneath them could only have been accomplished by the same means as before, and this exhaustion resulted in the preservation of those conditions most favorable to glaciation. When by the chilling of the oceans to about 31° Far. and by the glaciation of continental areas, the air was cleared of obscuring clouds and fogs, the wonderfully uniform series of climates was at an end.
With the dominion of solar heat there dawned upon our planet an era of climatic zones whose lines sensibly follow parallels of latitude; then also began seasons of spring, summer, autumn and winter, with the varying changes of the earth’s annual round.
The climatic changes during the control of earth heat, and within the range of geological research extended over eras:
- An era of torrid heat.
- An era of tropical heat.
- An era of temperate heat.
- An era of glacial cold.
Each merged gradually into the others, but each recorded its period of existence in unmistakable terms, all shrouded from the direct action of solar heat, and all evidencing by the life produced, the stifling, smothered character of the climate.
That solar heat was shut out from the surface of the earth during the Ice Age is geologically recorded in the glaciation of the North Temperate Zone over continental areas, where solar energy has removed glacial cold and established in its stead a mean annual temperature of 40° Far., and in the torrid zone it has removed glacial cold and established a mean annual temperature of 76° Far., where snow never falls.
Consequently, in a heated globe, constituted and circumstanced as the earth, exposed to two sources of heat, internal heat and solar heat, before its climates or surface temperature can pass under the control of solar heat climatic changes must be independent of latitude and the continental areas must be glaciated.