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THE SCIENTIFIC

MONTHLY

JANUARY, 1921
EARTH SCIENCES AS THE BACKGROUND

OF HISTORY
By JOHN C. MERRIAM
CARNEGIE INSTITUTION OF WASHINGTON

THE LARGER VIEW OF HISTORY THE concept of history as generally accepted has undergone extra

ordinary changes in recent years. History as read and taught has frequently expressed only in part the broader relations of events with a view to indicating their true bearing on the present. In its origin as a constructive science much of history was concerned with the emotional side of national propaganda, and in varying measure it has been an instrument used to promote a nationalistic spirit. Fortunately, we find many interpretations which have clearly stated the continuity of events, their real relations and significance in the world sense, and their proper trend.

Not less insufficient than the use to which history has often been put is in many instances the structure of the account presented. Continuity has not always been the fundamental factor. Descriptions of events in series, but unrelated, have at times formed the basis for discussion, and fundamental laws or scientific principles have not always played an important part.

Reaction against the incomplete view of historical study is in some measure due to application in human affairs of the hypothesis of evolution or development growing out of the fundamental historical sequence of geology as presented by Lyell and applied in the broad biological concept of Darwin. Assuming that man remains on a constant level, representing the type as created, human history might show indefinite fluctuations of movement; or it might be cyclic, each cycle representing approximately the same plane of development. According to the evolution hypothesis, the trend of the living world would be toward the more specialized, or more complicated, or more advanced. Although it might be cyclic, each cycle would rise to a

1Delivered as the Presidential Address before the Geological Society of America, December 29, 1919.

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higher stage, and the path would be helicoid. According to the developmental or evolution interpretation, every part of a historic sequence is related to every other part, and each feature of past series contributes somewhat to the interpretation of the present. This concept gives us for every portion of historic succession a formula, through which, with a certain degree of accuracy, the line may be projected forward. Viewed in this light, history becomes not merely a teacher by comparison or by analogy, but interprets the development of present conditions, and also furnishes a key to the future.

Rarely has the range of historical account included all major influences actually involved. Largely by reason of the fact that the world is so complicated, there is no connected statement which shows the happenings as a whole with their interlocking connections. The records are mainly pieces, or pieces of pieces, limited to one phase of the subject, restricted to one portion of the world, and covering only a small section of time. True world history scarcely exists. Analysis of the elements composing the fabric of history, considered in its enormous complication and as a world problem, shows that we cannot doubt the need for every item of knowledge which may be brought to bear for interpretation of our present situation and requirements. We must have these materials also for guidance of mankind in decisions on those greater problems demanding for their proper settlement a vision reaching over long periods and extending beyond the present generation. We should have light with increasing brilliance thrown into many dark corners. Present world questions will be solved in part by men who trade and those who study commerce, in part by men who rule and those who study ruler and politician. But the only view that can show us where we are and whither we go is one that, with other items, includes at least the outlines of the path over which we have come. The point of my story in this paper is that the farther back we see the path clearly, and the better we know our progress over it, the more certain we are to eliminate the minor curves and determine the true direction and the rate of speed to expect. I am suggesting that the deepest view of history is desirable for the purposes of fundamental decisions; that, no matter how far back this vision leads us, if it continues to add to knowledge of what we are by showing us how we came to be, it is needed and should be secured.

CoNTRIBUTION of THE SciENCEs To History

The sciences especially concerned with historic sequence are astronomy, geology, geography, paleontology, biology and anthropology. Astronomy, with its broad conceptions of stellar evolution, concerns us because it discusses the origin and early history of our planet. Geology and geography deal directly with the earth. Paleontology, representing biological history, must go to geology for its record. Anthropology has, as one of its most important phases, the history and origin of Inan.

The field of the astronomer, with its myriad bodies of the heavens, presumably represents wide range in development of the stellar systems within our view. Yet, with all our information as to the stages through which these bodies may proceed in their history, there is but little positive evidence on which we may depend. We may note modifications in the surface of the sun or in the clouds of Jupiter, or we may observe the varying brightness of the stars; but there is little in these variations which we have proved to be more than incidental fluctuation. Our knowledge of evolution of the stellar universe must depend largely upon comparisons of stars of various types, or of groups of stars and nebulae which we assume to represent incipient stellar systems. The nebular hypothesis, which has served to present a type of evolution of the solar system and a basis for interpretation of the origin of the earth, is called in question to such an extent as to be no longer acceptable to a large group of astronomers. The planetesimal hypothesis, developing similar world systems out of spiral nebulae, seems also to suffer under recent criticism. For practical comparisons in study of world evolution, we appear to have one of the most important sources of information in the history of our own planet. For the universe in the large we can prove little more than that there is shown a process of development for which almost infinite time seems required and in which cycles seem determined.

Our greatest scientific contributions to the study of history and of origins have come through geological and biological investigations. Geology is the greatest of historical sciences. From comparative and experimental studies alone biology makes large contribution, but its distinctly historical phase lies in the field of paleontology, in which the life record is read from the geological book. To geology and biology, furnishing together the life records, anthropological history must be added, reaching back, as it does, into geological history and expressing the beginnings of our account of human life and activity in terms of geology and paleontology.

For the purposes of this paper, geological history may be divided roughly into two portions. One, the later division, is represented in the known section of stratified rocks formed through the piling up of sediments and by the out-welling of molten material spread on the surface or squeezed into the strata. An earlier period expresses in a more doubtful manner the partly astronomic history of the earth antecedent to the record presented by the lowest or earliest known Strata.

The astronomic period of our earth's history is a subject for investigation by astronomer, physicist, chemist, and geologist. As yet the results of studies in this region are in large part of a speculative nature. The field furnishes one of the most attractive opportunities in science for further investigation. Although this phase of the problem has in it very much of fascination, the results are still of such a nature as to contribute little toward the objects of the present discussion. I shall therefore refer to geologic history only in terms of the distinct record extending to the lowest known strata in the second chapter of the account.

The length of the period which remains after elimination of the earlier or astronomic stage may be very short measured against the total age of the earth. We know that the lowest strata, wherever we find them, rest upon rocks which have been molten and in their molten state have destroyed the basement upon which the oldest known stratified rocks once rested. We admit, therefore, that not only have we lost the record before the earliest strata were formed, but that the earliest strata themselves have disappeared. The record remaining is, however, by no means brief in terms of human understanding. Few recent estimates have suggested that the section comprises less than two hundred thousand feet of strata, or that the time involved measures less than one hundred million years. This time may not be long compared with the entire age of the earth, and may not be more than a moment compared with the age of our solar system, but it furnishes all that we require for purposes of interpretation of human history.

Reduced to their simplest terms, the geological data of the stratified rocks give us a history relating to the accumulation of sediments, movements of the earth's crust, the making of continents and ocean basins, erosive agencies tending to wear down the land, volcanic activities, climatic changes, and life succession. This history presents, as its first significant lesson, the fact of instability of the earth's crust and the evidence that throughout geologic time, as we know it, the surface has shown diversity of form dependent upon movements of large magnitude. By offering opportunity for erosive forces to act, the movements which have produced continents and mountain ranges have also been responsible for accumulation of the sediments washed down to form the strata from which our record is read. Also intimately related to the succession of crustal movements is the history of igneous activity evidenced from time to time in the great extrusions of molten material forming successions of lava flows intercalated in the sedimentary series. The history of climate, furnished us through a great variety of data, gives evidence of almost continuously fluctuating conditions in the physics of the atmosphere, ranging between high and low humidity, and between temperatures comparable with those of the glacial periods and the climate of tropical or subtropical regions of the present day. The salient features of climatic history are the continuous change and the evidence of comparatively slight range of temperature for the earth as a whole within the span of geologic time as known. Earth history, as we see it in this record, shows from the most remote periods to the present constantly varying surface conditions dependent upon an unstable crust; continents and mountains arise only to be subject to the steady grind of erosion, wearing them away and spreading the débris over the seas. Always do we find land areas and seas, but with much variation as to size and form; always was the temperature near that of the present, though fluctuating from warmer and more humid to climates like that of the Glacial Period. Within the whole span of geological history and its continuous changes recorded, the phases of purely physical history presented do not show us in any of their various aspects definite progression or trend which may be described as an evolutionary process. It was once our practice to place emphasis on the geological history of the earth as the continuation of a graded or evolution series based on the succession of stages described in the nebular hypothesis. According to this view, we seemed to see in climatic evolution a gradual movement away from the conditions of the primitive heated earth and toward the present temperature of a cooling sphere. We once thought we saw the early atmosphere fit only for lower organisms and later cleared and purified for the higher types of life. With better understanding of climatic history, it comes out more and more distinctly that while the earth's climate fluctuated continuously, there is no clear evidence of definite progression through a series of stages dependent on gradual cooling of a once highly heated globe. So in other phases of purely physical history we have worked out what seemed at first to be evolution series, which have all proved finally to be nothing more than cycles that may be represented by variable formulae. As nearly as we can determine, the physical history of the earth within the span of time represented by our legible record has been so nearly stabilized as to show little or no variation which may not be considered merely as fluctuation rather than as evolution. As evidence of a continuously changing evolution series, the most extraordinary record of all history is that included in the paleontologic succession of life, running down through the story of geology, practi. cally to the beginning. Not only do we find the character of the earlier stratified rocks indicating atmospheric and climatic conditions similar to those now •btaining on the earth, but we find the rocks containing traces of living forms such as now are fitted to these climatic conditions. Throughout the whole stretch of the strictly geologic record, condi. tions in temperature and humidity evidently kept within the range

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