Geologic time

“ These three principal phenomena of the ice-fields, the mammals, and the human life and industry, together establish the chronology of the Age of Man. In other words, there are four ways of keeping prehistoric time: that of geology, that of palæontology, that of anatomy, and that of human industry. Geologic events mark the grander divisions of time; palæontologic and anatomic events mark the lesser divisions; while the successive phases of human industry mark the least divisions. ”

“ Not in their climates—for the climate of the globe seems to have been uniformly warm from pole to pole, without climatic zones, throughout the vast stretch of Palaeozoic and Mesozoic times—but in the succession of animal and vegetable life which they show. The rocks are the cemeteries of the different forms of life that have appeared upon the globe, and here the geologist reads their succession in time, and assigns them to his geologic horizons accordingly. ”

“ Now, as all historic records end, for each country, with the surface,—terminate at some point of man's history posterior to the preparation of that tract for his residence, we see how far more ancient than the historic date of the human race is the series of productions which lie below the surface. The limit of least antiquity of the scale of geological time is in every country beyond the date of the present surface. The series of strata is so ancient, that even its uppermost and newest term in every country is older than the race of man now existing there ”

“ The only value of such estimates is to define our notions of geological time, and to show that the enormous periods, of hundreds of millions of years, which have sometimes been indicated by geologists, are neither necessary nor warranted by the facts at our command; while the present result places us more in harmony with the calculations of physicists, by leaving a very wide margin between geological time as defined by the fossiliferous rocks, and that far more extensive period which includes all possibility of life upon the earth. ”

“ In the study of the many changes which have taken place in the history of the earth, a fundamental consideration is the determination of the relative ages of the rocks, especially the strata. How can the geologist assign a rock formation of any part of the earth to a particular age in the history of the earth? How can it be proved that certain rock formations in various parts of the earth originated practically at the same time? ”

“ While all hypotheses of the earth's beginnings are as yet unproved speculations, they serve to bring to mind one of the chief lessons which geology has to teach,—that the duration of the earth in time, like the extension of the universe in space, is vastly beyond the power of the human mind to realize. Behind the history recorded in the rocks, which stretches back for many million years, lies the long unrecorded history of the beginnings of the planet ”

“ The fossil remains of the Tertiary rocks, both animal and vegetable, present us with many instances of this kind.
The discussion of the distribution of animals and plants, when carried on in the light of geology, raises many interesting questions as to time, which we have already glanced at, but which deserve a little more attention. As to the vast duration of geological time all geologists are agreed. It is, however, now well understood that science sets certain limits to the time at our disposal. ”

“ As to the cosmical nature of the periods, while some geologists appear to regard the whole of geological time as a continuous evolution without any breaks, it is evidently more in accordance with facts to hold that there have been cycles of repose and activity succeeding each other, and that these have been of different grades. ”

“ No geologist will deny that the distance of time which separates some of the eras above alluded to, or the dates of the earliest and latest appearances of some of the fossils above mentioned, must be reckoned by millions of years. ”

“ Can you measure either of those intervals in the years of common chronology? Yet all over the world the succession of geological strata proclaims the recurrence over and over again of such intervals; silent, indeed, as to positive evidence, but widening the possible limits of time’s duration to the furthest stretch of fancy.
All our great continents have been ever so many times, either in the mass or piecemeal, under the waves of the ocean. Nothing hinders that the bed of every great ocean should have been ever so many times turned into dry land. ”

“ Computation of the Average Annual Amount of Subaërial Denudation.—The geology of the district above alluded to may assist our imagination in conceiving the extent to which groups of ancient rocks, each of which may in their turn have formed continents and oceanic basins, have been disturbed, folded, and denuded even in the course of a few out of many of those geological periods to which our imperfect records relate. It is not easy for us to overestimate the effects which causes in every day action must produce when the multiplying power of time is taken into account. ”

“ A lasting service will be rendered to our science if by well-concerted effort we can place geological dynamics and geological chronology on a broader and firmer basis of actual experiment and measurement than has yet been laid.
To understand aright the origin and progress of the dispute regarding the value of time in geological speculation, we must take note of the attitude maintained towards this subject by some of the early fathers of [Pg 200] the science. Among these pioneers none has left his mark more deeply graven on the foundations of modern geology than James Hutton. ”

“ But we have another system of chronology derived from a wholly different system of ideas; it too relates to periods of vast duration, and, like our great tidal periods, extends to times anterior to human history, or even to the duration of human life on this globe. The facts of geology open up to us a majestic chronology, the epochs of which are familiar to us by the succession of strata forming the crust of the earth, and by the succession of living beings whose remains these strata have preserved. ”

“ Hence, trifling as the results during a human life may appear, if we realize the multiplying influence of time we are led to perceive that the apparently feeble superficial agents can, in the course of ages, achieve stupendous transformations in the aspect of the land. If this efficacy may be deduced from what can be seen to be in progress now, it may not less convincingly be shown, from the nature of the sedimentary rocks of the earth’s crust, to have been in progress from the early beginnings of geological history. ”

“ It works out the chronological succession of the great formations of the earth’s crust, and endeavours to trace the sequence of events of which they contain the record. More particularly, it determines the order of succession of the various plants and animals which in past time have peopled the earth, and thus ascertains what has been the grand march of life upon this planet. ”

“ The belief that the mathematical physicist must be right in his views as to the age of the sun’s heat, and that there is no possibility of a longer period being admitted, seems at present to be leading geologists towards the opposite extreme in regard to the length of geological time. Attempts have been recently made to compress the geological history of our globe into the narrow space allotted by the physicist. ”

“ Though this epoch is incredibly more remote than any historical record, it is perhaps not incomparable with the duration of the human race; while compared with the vast lapse of geological time, such periods seem trivial and insignificant. Geologists have long ago repudiated mere thousands of years; they now claim millions, and many millions of years, for the performance of geological phenomena. ”

“ To say that man lived in the Glacial Age, and that we have some faint traces of his presence in still earlier periods, after all conveys to our minds only vague ideas of a far-away time. The more a geologist studies the structure of the earth, the more impressed is he with the magnitude of the time that must have passed since “The Beginning.” ”

“ Modern geology and archæology have rendered valuable assistance toward its solution, and at the present stage of these sciences it seems most probable that the time of man's advent must be placed in the tertiary or in the beginning of the diluvial age. ”

“ The arguments from the geological side against the physical contention that would limit the age of our globe to some 10 or 20 millions of years are mainly based on the observed rates of geological and biological changes at the present time upon land and sea, and on the nature, physical history and organic contents of the stratified crust of the earth. ”

“ The fundamental character of the period we are about to study is the immense development of a vegetation which then covered much of the globe. The great thickness of the rocks which now represent the period in question, the variety of changes which are observed in these rocks wherever they are met with, lead to the conclusion that this phase in the Earth’s history involved a long succession of time. ”

“ For certainly on my theory such strata must somewhere have been deposited at these ancient and utterly unknown epochs in the world's history.
I can answer these questions and grave objections only on the supposition that the geological record is far more imperfect than most geologists believe. It cannot be objected that there has not been time sufficient for any amount of organic change; for the lapse of time has been so great as to be utterly inappreciable by the human intellect. ”

“ For, just at the close of the first quarter of the nineteenth century, geologists began to examine the caves and beds of drift in various parts of the world; and within a few years from that time a series of discoveries began in France, in Belgium, in England, in Brazil, in Sicily, in India, in Egypt, and in America, which established the fact that a period of time much greater than any which had before been thought of had elapsed since the first human occupation of the earth. ”

“ And of this the whole science of geology affords the demonstration. If the rocks have been formed in succession, as geology has proved, and twenty miles of strata have been piled over the earliest-appearing forms of life, then the time since living creatures came has been indefinitely vast, and that the periods are not amenable to anything like "calculation" or trustworthy estimate is shown by the way the subject is dealt with in our most authoritative geological works. ”

“ The conditions of life must have been greatly modified by these geographical changes. The life-forms bear testimony to this changed condition. Old forms die away, and are succeeded by those approaching more nearly our own times. The name of this period is the Mesozoic time, or the period of middle life forms.14 It is instructive to notice the steady advance in the type of life, both animal and vegetable. The abundant flowerless vegetation of the coal formation of the preceding epoch dwindles away. ”

“ The terms used for the more important divisions of geological time are, in descending order of magnitude, era, period, epoch, age or stage, and the general scheme of the eras and periods, which is in almost uniform use throughout the world, is given in the table, which is arranged so as to give the succession graphically, with the most ancient rocks at the bottom and the latest at the top. ”

“ In studying the various geological agencies we must remember the almost inconceivable times in which they work. The slowest process when multiplied by the immense time in which it is carried on produces great results. The geologist looks upon the land forms of the earth’s surface as monuments which record the slow action of weathering and other agents during the ages of the past. ”

“ Independently altogether of human history, these are two geological ages distinguished by different physical conditions and different species of animals; and the time has undoubtedly come when all the speculations of archæologists respecting early man must be regulated by these great geological facts, which are stamped upon those later deposits of the crust of the earth, which have been laid down since man was its inhabitant. ”

“ Geologists call the last great geological period the Pleistocene. It began somewhere between a half million and a million years ago, and was a time of great changes. Sometimes we call it the Ice Age, for in the Pleistocene there were at least three or four times when large areas of earth were covered with glaciers. The reason for my uncertainty is that while there seem to have been four major mountain or alpine phases of glaciation, there may only have been three general continental phases in the Old World.2 ”

“ If we knew the total quantity of stratified rock on the globe, we could easily tell the time that would be required for its formation. Most geologists would, I believe, be inclined to admit that, if spread uniformly over the entire globe, it would form a layer of at least 1,000 feet in thickness. In such a case the time required for its deposition would be as follows:
1,000 × 6,000 × 4 = 24,000,000 years. ”

“ Different geologists, proceeding from different premises, have sought to estimate the duration of the above-named creative period, and vary from a million to nine million years.——The time during which the earth generated organic beings is again small when compared with the ages during which the world was a ball of fused rocks. ”

“ Geological terms convey to us no definite ideas as to the lapse of time, and we have an instinctive desire to substitute for them some term of years. In most cases this is impossible, as we have no means to measure the flight of past time, nor are we yet prepared to discuss the question of time, since to do so we must learn a great deal more about the cause of the Glacial Age. ”