Conclusion
Here we must bring this study of the earth's evolution to a close. Its
fundamental principle has been that the present, if rightly understood,
affords a full key to the past. With this as a guide we have touched on
many hypotheses, some essential and some unessential to the general line
of thought. The first main hypothesis is that the earth's present
climatic variations are correlated with changes in the solar atmosphere.
however, that it ranks as a theory rather than as an hypothesis. Next
comes the hypothesis that variations in the solar atmosphere influence
the earth's climate chiefly by causing variations not only in
temperature but also in atmospheric pressure and thus in storminess,
wind, and rainfall. This, too, is one of the essential foundations on
which the rest of the book is built, but though this cyclonic hypothesis
is still a matter of discussion, it seems to be based on strong
evidence. These two hypotheses might lead us astray were they not
balanced by another. This other is that many climatic conditions are due
to purely terrestrial causes, such as the form and altitude of the
lands, the degree to which the continents are united, the movement of
ocean currents, the activity of volcanoes, and the composition of the
atmosphere and the ocean. Only by combining the solar and the
terrestrial can the truth be perceived. Finally, the last main
hypothesis of this book holds that if the climatic conditions which now
prevail at times of solar activity were magnified sufficiently and if
they occurred in conjunction with certain important terrestrial
conditions of which there is good evidence, they would produce most of
the notable phenomena of glacial periods. For example, they would
explain such puzzling conditions as the localization and periodicity of
glaciation, the formation of loess, and the occurrence of glaciation in
low latitudes during Permian and Proterozoic times. The converse of this
is that if the conditions which now prevail at times when the sun is
relatively inactive should be intensified, that is, if the sun's
atmosphere should become calmer than now, and if the proper terrestrial
conditions of topographic form and atmospheric composition should
prevail, there would arise the mild climatic conditions which appear to
have prevailed during the greater part of geological time. In short,
there seems thus far to be no phase of the climate of the past which is
not in harmony with an hypothesis which combines into a single unit the
three main hypotheses of this book, solar, cyclonic, and terrestrial.
Outside the main line of thought lie several other hypotheses. Several
of these, as well as some of the main hypotheses, are discussed chiefly
in Earth and Sun, but as they are given a practical application in
this book they deserve a place in this final summary. Each of these
secondary hypotheses is in its way important. Yet any or all may prove
untrue without altering our main conclusions. This point cannot be too
strongly emphasized, for there is always danger that differences of
opinion as to minor hypotheses and even as to details may divert
attention from the main point. Among the non-essential hypotheses is the
idea that the sun's atmosphere influences that of the earth electrically
as well as thermally. This idea is still so new that it has only just
entered the stage of active discussion, and naturally the weight of
opinion is against it. Although not necessary to the main purpose of
this book, it plays a minor role in the chapter dealing with the
relation of the sun to other astronomical bodies. It also has a vital
bearing on the further advance of the science of meteorology and the art
of weather forecasting. Another secondary hypothesis holds that sunspots
are set in motion by the planets. Whether the effect is gravitational or
more probably electrical, or perhaps of some other sort, does not
concern us at present, although the weight of evidence seems to point
toward electronic emissions. This question, like that of the relative
parts played by heat and electricity in terrestrial climatic changes,
can be set aside for the moment. What does concern us is a third
hypothesis, namely, that if the planets really determine the periodicity
of sunspots, even though not supplying the energy, the sun in its flight
through space must have been repeatedly and more strongly influenced in
the same way by many other heavenly bodies. In that case, climatic
changes like those of the present, but sometimes greatly magnified, have
presumably arisen because of the constantly changing position of the
solar system in respect to other parts of the universe. Finally, the
fourth of our secondary hypotheses postulates that at present the date
of movements of the earth's crust is often determined by the fact that
storms and other meteorological conditions keep changing the load upon
first one part of the earth's surface and then upon another. Thus
stresses that have accumulated in the earth's isostatic shell during the
preceding months are released. In somewhat the same way epochs of
extreme storminess and rapid erosion in the past may possibly have set
the date for great movements of the earth's crust. This hypothesis, like
the other three in our secondary or non-essential group, is still so new
that only the first steps have been taken in testing it. Yet it seems to
deserve careful study.
In testing all the hypotheses here discussed, primary and secondary
alike, the first necessity is a far greater amount of quantitative work.
In this book there has been a constant attempt to subject every
hypothesis to the test of statistical facts of observation.
Nevertheless, we have been breaking so much new ground that in many
cases exact facts are not yet available, while in others they can be
properly investigated only by specialists in physics, astronomy, or
mathematics. In most cases the next great step is to ascertain whether
the forces here called upon are actually great enough to produce the
observed results. Even though they act only as a means of releasing the
far greater forces due to the contraction of the earth and the sun, they
need to be rigidly tested as to their ability to play even this minor
role. Still another line of study that cries aloud for research is a
fuller comparison between earthquakes on the one hand and meteorological
conditions and the wandering of the poles on the other. Finally, an
extremely interesting and hopeful quest is the determination of the
positions and movements of additional stars and other celestial bodies,
the faint and invisible as well as the bright, in order to ascertain the
probable magnitude of their influence upon the sun and thus upon the
earth at various times in the past and in the future. Perhaps we are
even now approaching some star that will some day give rise to a period
of climatic stress like that of the fourteenth century, or possibly to a
glacial epoch. Or perhaps the variations in others of the nearer stars
as well as Alpha Centauri may show a close relation to changes in the
sun.
Throughout this volume we have endeavored to discover new truth
concerning the physical environment that has molded the evolution of all
life. We have seen how delicate is the balance among the forces of
nature, even though they be of the most stupendous magnitude. We have
seen that a disturbance of this balance in one of the heavenly bodies
may lead to profound changes in another far away. Yet during the billion
years, more or less, of which we have knowledge, there appears never to
have been a complete cataclysm involving the destruction of all life.
One star after another, if our hypothesis is correct, has approached the
solar system closely enough to set the atmosphere of the sun in such
commotion that great changes of climate have occurred upon the earth.
Yet never has the solar system passed so close to any other body or
changed in any other way sufficiently to blot out all living things. The
effect of climatic changes has always been to alter the environment and
therefore to destroy part of the life of a given time, but with this
there has invariably gone a stimulus to other organic types. New
adaptations have occurred, new lines of evolutionary progress have been
initiated, and the net result has been greater organic diversity and
richness. Temporarily a great change of climate may seem to retard
evolution, but only for a moment as the geologist counts time. Then it
becomes evident that the march of progress has actually been more rapid
than usual. Thus the main periods of climatic stress are the most
conspicuous milestones upon the upward path toward more varied
adaptation. The end of each such period of stress has found the life of
the world nearer to the high mentality which reaches out to the utmost
limits of space, of time, and of thought in the search for some
explanation of the meaning of the universe. Each approach of the sun to
other bodies, if such be the cause of the major climatic changes, has
brought the organic world one step nearer to the solution of the
greatest of all problems,--the problem of whether there is a psychic
goal beyond the mental goal toward which we are moving with ever
accelerating speed. Throughout the vast eons of geological time the
adjustment of force to force, of one body of matter to another, and of
the physical environment to the organic response has been so delicate,
and has tended so steadily toward the one main line of mental progress
that there seems to be a purpose in it all. If the cosmic uniformity of
climate continues to prevail and if the uniformity is varied by changes
as stimulating as those of the past, the imagination can scarcely
picture the wonders of the future. In the course of millions or even
billions of years the development of mind, and perhaps of soul, may
excel that of today as far as the highest known type of mentality excels
the primitive plasma from which all life appears to have arisen.
More
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Causes Of Mild Geological Climates
In discussions of climate, as of most subjects, a peculiar psychological phenomenon is observable. Everyone sees the necessity of explaining conditions different from those that now exist, but few realize that present conditions may be abnormal, a... Conclusion
Here we must bring this study of the earth's evolution to a close. Its fundamental principle has been that the present, if rightly understood, affords a full key to the past. With this as a guide we have touched on many hypotheses, some essential ... Glaciation According To The Solar-cyclonic Hypothesis[38]
The remarkable phenomena of glacial periods afford perhaps the best available test to which any climatic hypothesis can be subjected. In this chapter and the two that follow, we shall apply this test. Since much more is known about the recent Grea... Hypotheses Of Climatic Change
The next step in our study of climate is to review the main hypotheses as to the causes of glaciation. These hypotheses apply also to other types of climatic changes. We shall concentrate on glacial periods, however, not only because they are the ... Post-glacial Crustal Movements And Climatic Changes
An interesting practical application of some of the preceding generalizations is found in an attempt by C. E. P. Brooks[95] to interpret post-glacial climatic changes almost entirely in terms of crustal movement. We believe that he carries the mat... Some Problems Of Glacial Periods
Having outlined in general terms the coming of the ice sheets and their disappearance, we are now ready to discuss certain problems of compelling climatic interest. The discussion will be grouped under five heads: (I) the localization of glaciatio... Terrestrial Causes Of Climatic Changes
The major portion of this book has been concerned with the explanation of the more abrupt and extreme changes of climate. This chapter and the next consider two other sorts of climatic changes, the slight secular progression during the hundreds of... The Changing Composition Of Oceans And Atmosphere
Having discussed the climatic effect of movements of the earth's crust during the course of geological time, we are now ready to consider the corresponding effects due to changes in the movable envelopes--the oceans and the atmosphere. Variations ... The Climate Of History
We are now prepared to consider the climate of the past. The first period to claim attention is the few thousand years covered by written history. Strangely enough, the conditions during this time are known with less accuracy than are those of geolo... The Climatic Stress Of The Fourteenth Century
In order to give concreteness to our picture of the climatic pulsations of historic times let us take a specific period and see how its changes of climate were distributed over the globe and how they are related to the little changes which now tak... The Earth's Crust And The Sun
Although the problems of this book may lead far afield, they ultimately bring us back to the earth and to the present. Several times in the preceding pages there has been mention of the fact that periods of extreme climatic fluctuations are closel... The Effect Of Other Bodies On The Sun
If solar activity is really an important factor in causing climatic changes, it behooves us to subject the sun to the same kind of inquiry to which we have subjected the earth. We have inquired into the nature of the changes through which the eart... The Origin Of Loess
One of the most remarkable formations associated with glacial deposits consists of vast sheets of the fine-grained, yellowish, wind-blown material called loess. Somewhat peculiar climatic conditions evidently prevailed when it was formed. At prese... The Solar Cyclonic Hypothesis
The progress of science is made up of a vast succession of hypotheses. The majority die in early infancy. A few live and are for a time widely accepted. Then some new hypothesis either destroys them completely or shows that, while they contain ele... The Sun's Journey Through Space
Having gained some idea of the nature of the electrical hypothesis of solar disturbances and of the possible effect of other bodies upon the sun's atmosphere, let us now compare the astronomical data with those of geology. Let us take up five chie... The Uniformity Of Climate
The role of climate in the life of today suggests its importance in the past and in the future. No human being can escape from the fact that his food, clothing, shelter, recreation, occupation, health, and energy are all profoundly influenced by h... The Variability Of Climate
The variability of the earth's climate is almost as extraordinary as its uniformity. This variability is made up partly of a long, slow tendency in one direction and partly of innumerable cycles of every conceivable duration from days, or even hou...