sufficient supply of heat to hold mean temperatures at a higher degree
of heat than 32° Far. this isotherm shrunk to the surface only to
be removed by solar heat. Since the position of this isotherm was
independent of latitude its intersections with the surface depended
only upon elevation, and as the continents lost their heat more rapidly
than oceans, the latter were the last to fall to 32° Far.
As in previous eras torrid, tropical and temperate life had existed
in Spitzbergen, France and Brazil independent of the latitudes of
these countries, so too were glacial conditions equally independent of
latitudes. But in the removal of glacial conditions the isotherms of
solar climates were necessarily followed.
Thus the Ice Age marks the date at which the climates of the globe
passed from the control of earth heat to that of solar heat. The great
specific heat of water retained in the oceans, the energy necessary to
maintain the cloud shield shutting out solar heat until both land and
ocean areas could be equally cooled and contracted, thus ensuring the
maximum degree of thickness and stability to the crust. The mysteries
of geological climates, interpreted by known laws, applicable alike to
all members of the solar system, develop thus into a system beautiful
in its simplicity.
Once realize that the surface temperatures of the globe were at one era
in the past too high, by reason of _internal heat_, to permit water to
remain upon the surface, and the peculiar properties possessed by the
various forms of water and their relations to heat and cold, and follow
out these facts to their natural and logical conclusion, and the whole
mystery of geological climates clears up and becomes simple.
MATHEMATICAL CALCULATIONS AS TO THE DURATION OF EARTH HEAT.
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. An erroneous assumption of the manner in which heat is lost by a
planet, upon which there exists an atmosphere and a fluid possessing
the physical properties of water.
2. No account is taken in these calculations of the heat set free by
denudations, etc.
3. The conservative action of active exterior sources is not
considered.
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.”
ASTRONOMICAL CAUSES AND THEIR INFLUENCE.
We will now consider the effect of astronomical causes. Dr. Croll has
elaborately discussed the variations in solar exposure to which the two
hemispheres of our planet have been and are subjected.[23]
The distinguished Astronomer Royal of the Dublin Observatory, Dr.
Ball, has shown that 63% of the gross solar energy received by
either hemisphere reaches it during summer and the remaining 37%
during winter.[24] High authorities, both before and since these
publications, have discussed various phases of these influences, as
well as offered remarkable and unverifiable hypotheses regarding the
temperature of space, solar energy, and the heat absorptive power of
a solar envelope.[25] It is not necessary to attempt a discussion or
elaboration of these views. Should the interpretation herein rendered
be correct, it follows that variations in the distance from or
degree of solar energy could not have directly affected the surface
temperatures of the globe prior to the culmination of the Ice Age, and
that only since that age could these slight variations have acted,
except in a conservative way. It is unquestionable that for many
years past the temperature of the northern hemisphere has risen more
rapidly than the southern. This condition is proved not only by correct
deductions from actual conditions and laws, but by observation. This is
also recorded geologically by the greater removal of glacial conditions
in the northern hemisphere--although in both this removal is yet in
progress.
In a globe wrapped in a mass of vapor by reason of evaporation
maintained at the surface by its own heat and condensed upon the
outer surface of the spheroidal cloud envelope, it is immaterial so
far as surface temperatures are concerned, to what degree of outside
heat it may be subjected. The only possible effects of variations in
the distance from, or intensity of the exterior heat source being
to influence the duration of the interior supply and the distance
therefrom at which cloud condensation takes place.
In a globe thus enshrouded the same order of surface temperatures
would follow, whether revolving in the orbit of Venus or that of
Neptune--the actual influences being the greater rate of loss in the
remoter position, the more rapid succession of geological climates, and
the greater time necessary for the removal of glacial conditions, and
for the establishment of solar climatic control. Could the earth have
been removed during the Archæan Age to the orbit of Jupiter without
disturbing other conditions, no change could have occurred in the order
of succeeding geological climates prior to the Ice Age. The rate of
receipt of solar energy would have been in the ratio of (5.2)²:1; and
the actual retardation of loss would have been in this ratio, as also
the rate of establishment of solar climatic control; the crust would
have cooled quicker, and therefore have been thinner and less stable
than at present.
The observed movements in the cloud envelope of Jupiter
present phenomena warranting the belief that his atmosphere is
non-transcalent.[26] In this particular it resembles the clouded
atmosphere of the earth; and indicates a condition analogous to that
of the earth in pre-glacial ages. The smaller planets by reason
of their lesser masses have lost their available resident heat.
Their atmospheres have become cleared and are both translucent and
transcalent. Their surfaces can be observed, and their volumes and
densities calculated with a reasonable degree of exactness. In the
cases of the larger planets observations are confined to the surface
of their spheroidal cloud envelopes, and hence to these planets are
ascribed volumes and densities varying abnormally from those whose
actual volumes can be measured. The satellites of Jupiter possess
much greater densities than that ascribed to the great planet--were
it possible to measure the actual volume of his enshrouded mass this
apparent anomaly would be in whole or in part removed.
Not knowing the surface temperatures, the exact composition of the
atmospheres, nor the dimensions of the planetary masses, the distances
to which the cloud envelopes of Jupiter, Saturn, Uranus and Neptune may
be expanded, are yet matters of conjecture. Whatever is known of these
planets corroborates the interpretation herein rendered of the record
of the geological climates of the earth.[27]
THE ESTABLISHMENT OF SOLAR CLIMATES.
At the culmination of the Ice Age the snow line was much lower than at
present, and elevated lands[28] at all latitudes were deeply glaciated;
the seas were intensely cold. It is evident that since the culmination
of the Ice Age and in the establishment of the present climates there
has been a great rise in temperatures in the tropical, temperate and
sub-frigid zones. There is also indisputable evidence that this rise in
temperature is yet in progress. This accession of heat must therefore
be accounted for by the correct application of laws and forces now
acting, and it is not necessary to go outside of these known laws and
forces to render a correct interpretation of the establishment and
maintenance of the zones of climate now existing.
It will be observed that when the oceans were exhausted of their heat
and the lands deeply glaciated, the crust was shrunk in upon the
interior mass by being uniformly chilled down to the lowest temperature
to which a planet, upon which water and an atmosphere exist, can be
subjected. The atmosphere was then cleared of clouds and heat rays from
exterior sources permitted to reach the planetary surface. At once
these rays began to be changed into dark heat rays, particularly those
from water, and the trapping of heat ensued; from this date a general
rise in temperatures must follow from the accession of heat from
exterior sources, until checked within the moderate limits hereafter
outlined.
The trapping process thus inaugurated is independent of the actual
amount of heat received whether from solar or stellar sources.
Were it possible for the now pent-up internal heat to raise the
temperature of the oceans, the crust at the bottom of the oceans, and
under the polar ice caps to a mean temperature of say 68 degrees Far.,
the accession of heat from exterior sources would be shut off, as in
early Quaternary times, by dense clouds; the exterior would be again
shrunk by glacial conditions, the air cleared as before and heat from
exterior sources in whatever amounts it then reached the surface would
be trapped as succeeded the Ice Age.
This action must in turn take place upon any planet upon which water
and an atmosphere resembling ours exist. The rate at which a planet
acquires heat from exterior sources is dependent upon the power of its
atmosphere to trap heat; very slight variations in the atmospheric
constituents producing great variations in heat trapping power.
The trapping process not being a function of the orbital distance, nor
of the actual amount of heat received, but of the composition of the
atmosphere, this rise, being only a function of the amount received and
not of the trapping process, this rise in temperature is as certain to
follow in one position as another.
By thus being subjected to the maximum shrinking-strains the weakest
portions of the crust were ruptured. The lava ejected from these
ruptures was spread out over the weak areas in successive layers of
a few dozen feet in thickness until the added strength reached that
belonging to thousands of feet of solid rock.[29]
To digress a moment--
These lava overflows evidently performed another important function.
The heat set free by each successive layer could not have been lost
by radiation into space, for the enshrouding clouds had not yet been
removed. The air and clouds caught this heat and bearing it eastwardly
in their general course caused warm rains instead of snow to be
precipitated upon the adjacent region. In this way the “unglaciated
area” escaped glaciation; in this area are the “bad lands” of Dakota,
whose topography distinctly shows that sub-aerial denudation, and not
glacial ice formed the controlling features. In this area are the great
deposits of tertiary fossil life, in perfect form--uncrushed by the
mighty tread of the glaciers which surrounded them on all sides, except
to the west. From areas such as these went forth the life that survived
the glacial winter.
That the isotherm marked by glacial ice is yet slowly retreating upward
is recorded not only by tradition and history but geologically and
physically, as observed by every scientist who has studied existing
glaciers.[30]
This retreat is a positive proof of either a decrease in precipitation
on the tributary areas, a rise in temperature, or both of these
agencies acting conjointly. There is no evidence to show that a
decrease in precipitation[31] is synchronously taking place over the
sub-frigid, temperate and tropical regions of both hemispheres, as
is the retreat of glaciers; and there are positive and active causes
in force which have affected, and are yet affecting an increase in
temperature. We must therefore conclude that this rise in the isotherm
marking glacial ice is due primarily, if not entirely, to an accession
of heat.
It has been demonstrated that at the culmination of the Ice Age,
much colder conditions existed than at present. It now remains to
explain the conditions acting to bring about existing climates. Upon
the exhaustion of the last available remnant of earth heat--left in
the oceans by reason of the high specific heat of water--the supply
of vapor maintaining the cloud envelope was shut off, and solar heat
permitted to reach the planetary surface.
That direct solar rays are converted into obscure or dark heat rays
by contact with the planetary surface, and that the atmosphere of
our planet is more transcalent to the former than to the latter, has
been fully demonstrated by Tyndall,[32] although slightly modified by
Buff.[33]
However small may be the difference between the transcalency of the
atmosphere to direct solar rays and to the dark rays into which the
direct are converted, a gradual rise in temperature must follow. This
rise must follow whether solar energy be constant or slowly decreasing,
the rise being due not to the actual amount of heat received, but to
the difference between the rate of receipt and the rate of loss.
The great increase of mean surface temperatures in equatorial,
temperate and sub-tropical areas being due to this small but positive
difference between the rates of receipt and loss; as has just been
shown, this action is yet in progress.
These deductions are radically at variance with the opinion of
high authorities on meteorology, as may be seen from the following
quotation: “It is evident that our planet, considered as a whole, and
on the average of many years, loses all the heat that it receives from
the sun, but all the details of this process have not yet been worked
out.[34]”
The author is unable to find any facts to sustain this view--all
tend to refute it. The trapping of heat by vapors and gases of the
atmosphere--the gradual retreat of glaciers in both hemispheres--and
the vast rise in temperatures since the culmination of the Ice Age--all
conclusively tend to corroborate the deductions just reached--namely,
that the mean surface temperatures of the globe have been and are yet
rising from the trapping of heat.
It does not follow that this rise has an indefinite or excessive limit,
as the oceans become warmer they are cooled by giving off more vapor.
This vapor, when partly condensed into clouds, intercepts solar heat
in the upper atmosphere, and the intense white of the upper surface of
clouds reflects more heat into space than the darker planetary surface
beneath.[35]
The vast store of cold in the continental ice sheets has been
greatly exhausted; there yet remains the vaster store in the ice
cold depths of the oceans, the conservative influence of which
cannot be estimated; for besides the difficulties of heating water
from the surface downwards, there yet remains the cooling effect of
surface evaporation. There is thus presented the extreme slowness
of the methods by which vast changes are wrought. Here are agencies
whose results are so slight as not to be detected by thermometric
methods--yet recording their effects in grand eras of climates
throughout the earth.
The planet Mars is particularly interesting, having a mass less
than one-ninth (1/9.4) that of the earth. His loss of internal heat
occurred ages before that of the earth; therefore, Mars has been a
heat-gathering body longer than the earth, and enjoys a milder general
temperature,[36] although that planet receives less than half the heat
and light received by the earth. Jupiter is in a condition which our
geological history proves the earth to have passed through; Mars is in
a condition towards which the earth is gradually tending.[37]
It is now a simple matter to trace the steps by which glacial
conditions were removed and zones of climate established.
Solar energy first established its control in that zone most exposed to
its power--namely, the torrid zone. From this zone glacial conditions
were first removed, and this removal continued north and south upon
lines parallel with present isotherms.
In considering the astronomical causes, and the physical results
thereby brought about, it was argued that these causes tended to heat
the northern hemisphere more rapidly than the southern. Dr. Croll and
other physicists, have so fully discussed this question that there
remains but little to be added.
The prime reason, however, seems to have been omitted, which is simply
this, the northern hemisphere, containing so large a predominance of
land area, was more easily warmed than the southern. This unequal
heating once inaugurated would establish currents both of air and water
tending to perpetuate this action, reinforced as it is by geographical
and cosmical agencies.
When, by this gradual accession of heat, conditions and temperatures
resembling those existing prior to the Ice Age, were re-established,
we find these new conditions restricted to latitudinal belts
sensibly parallel with the equator, but modified by elevation and
ocean currents; whereas the corresponding pre-glacial climates were
independent of latitude.
By the trapping of solar heat a gradual rise in temperature was
inaugurated at that period, when by the exhaustion of the earth heat,
left in the oceans, the enshrouding clouds were removed. Then, and not
until then, do we find the removal of conditions shutting out solar
heat written in zones of life belting the earth. In these new zones of
climate there have been developed higher, nobler types of life, and
with the birth of the seasons there was ushered in upon the earth that
Light which is developing Psychozoic Life.
FOOTNOTES
[1] In 1821 Venetz called attention to the once greater extension of
Glaciers; and in 1824 Prof. Esmark made similar observations as to the
Glaciers of Norway. Phil. Mag., Vol. XXVII, p. 321.
As early as 1821 a prize of 300 livres was offered by the Helvitic
Soc. of Nat. Sci. for the collection of facts regarding the increase
or decrease of the extension of glaciers in the Alps. Tillock’s Phil.
Mag., Vol. LVII, p. 307.
But to Agassiz belongs the honor of having first pointed out the
existence of _the_ Ice Age when _all_ glaciers were vastly more
extended than at present.
[2] The writer prefers the nomenclature of Dr. Geikie and others using
the term Ice Age rather than Glacial Epoch, or Period. The duration
of this age was not recorded in the same manner and terms as either
previous or succeeding ages; this is due to the inactivity, or even
absolute suspension of the great forces, heat and moisture, over
continental areas during this age; under estimates of its duration are
thus liable to be made.
[3] This question is so important and has so broad a bearing that it
will be reverted to later under the heading _Palæozoic Glaciation_.
[4] Transactions of the Technical Society of the Pacific Coast,
Sept., 1891, Vol. VIII. See also The Climate Controversy, S. V.
Wood, Jr., Geol. Mag., 1876 and 1883. Climate and Time, Climate and
Cosmology, Croll. Island Life, Alfred Russell Wallace, F. R. S.,
etc. Philosophical Magazine, May, 1864. British Association Reports,
part 2, p. 11. Proceedings Royal Soc., vol. xxviii, p. 15. Quart.
Jour. Geological Soc., Feb., 1878. Nature, July 4, 1878. Trans.
Geological Soc., Glasgow, Feb. 22, 1877. The Ice Age in North America,
Dr. Fred. G. Wright, Appendix by Warren Upham. The Cause of an Ice
Age, Sir Robert Ball, F. R. S., etc. Révolutions de la Mer. Déluges
Périodiques, Alphonse Joseph Adhémar.
[5] See also _The Date of the Last Glacial Epoch_. Gen. Drayson, R. A.
Science, Nov. 25, 1892.
[6] Elements of Geology, Le Conte, 2d Edition, page 578.
[7] Stellar heat having the same function as solar heat, and being
sensibly a constant of unknown amount but much less than solar heat,
need not be separately considered in further discussion of the question.