The Birth-Time of the World and Other Scientific Essays Part 1

The Birth-Time of the World and Other Scientific Essays.

by J. (John) Joly.

PREFACE

Tins volume contains twelve essays written at various times during recent years. Many of them are studies contributed to Scientific Reviews or delivered as popular lectures. Some are expositions of views the scientific basis of which may be regarded as established. Others--the greater number--may be described as attempting the solution of problems which cannot be approached by direct observation.

The essay on The Birth-time of the World is based on a lecture delivered before the Royal Dublin Society. The subject has attracted much attention within recent years. The age of the Earth is, indeed, of primary importance in our conception of the longevity of planetary systems. The essay deals with the evidence, derived from the investigation of purely terrestrial phenomena, as to the period which has elapsed since the ocean condensed upon the Earth's surface. Dr. Decker's recent addition to the subject appeared too late for inclusion in it. He finds that the movements (termed isostatic) which geologists recognise as taking place deep in the Earth's crust, indicate an age of the same order of magnitude

as that which is inferred from the statistics of denudative history.[1]

The subject of _Denudation_ naturally arises from the first essay.

In thinking over the method of finding the age of the ocean by the acc.u.mulation of sodium therein, I perceived so long ago as 1899, when my first paper was published, that this method afforded a means of ascertaining the grand total of denudative work effected on the Earth's surface since the beginning of geological time; the resulting knowledge in no way involving any a.s.sumption as to the duration of the period comprising the denudative actions. This idea has been elaborated in various publications since then, both by myself and by others.

"Denudation," while including a survey of the subject generally, is mainly a popular account of this method and its results. It closes with a reference to the fascinating problems presented by the inner nature of sedimentation: a branch of science to which I endeavoured to contribute some years ago.

_Mountain Genesis_ first brings in the subject of the geological intervention of radioactivity. There can, I believe, be no doubt as to the influence of transforming elements upon the developments of the surface features of the Earth; and, if I am right, this source of thermal energy is mainly responsible for that local acc.u.mulation of wrinkling which we term mountain chains. The

[1] Bull. Geol. Soc. America, vol. xxvi, March 1915.

paper on _Alpine Structure_ is a reprint from "Radioactivity and Geology," which for the sake of completeness is here included. It is directed to the elucidation of a detail of mountain genesis: a detail which enters into recent theories of Alpine development.

The weakness of the theory of the "horst" is manifest, however, in many of its other applications; if not, indeed, in all.

The foregoing essays on the physical influences affecting the surface features of the Earth are accompanied by one ent.i.tled _The Abundance of Life._ This originated amidst the overwhelming presentation of life which confronts us in the Swiss Alps. The subject is sufficiently inspiring. Can no fundamental reason be given for the urgency and aggressiveness of life? Vitality is an ever-extending phenomenon. It is plain that the great principles which have been enunciated in explanation of the origin of species do not really touch the problem. In the essay--which is an early one (1890)--the explanation of the whole great matter is sought--and as I believe found--in the att.i.tude of the organism towards energy external to it; an att.i.tude which results in its evasion of the r.e.t.a.r.dative and dissipatory effects which prevail in lifeless dynamic systems of all kinds.

_Other Minds than Ours_? attempts a solution of the vexed question of the origin of the Martian "ca.n.a.ls." The essay is an abridgment of two popular lectures on the subject. I had previously written an account of my views which carried the enquiry as far as it was in

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my power to go. This paper appeared in the "Transactions of the Royal Dublin Society, 1897." The theory put forward is a purely physical one, and, if justified, the view that intelligent beings exist in Mars derives no support from his visible surface features; but is, in fact, confronted with fresh difficulties.

_Pleochroic Haloes_ is a popular exposition of an inconspicuous but very beautiful phenomenon of the rocks. Minute darkened spheres--a microscopic detail--appear everywhere in certain of the rock minerals. What are they? The discoveries of recent radioactive research--chiefly due to Rutherford--give the answer. The measurements applied to the little objects render the explanation beyond question. They turn out to be a quite extraordinary record of radioactive energy; a record acc.u.mulated since remote geological times, and a.s.suring us, indirectly, of the stability of the chemical elements in general since the beginning of the world. This a.s.surance is, without proof, often a.s.sumed in our views on the geological history of the Globe.

Skating is a discourse, with a recent addition supporting the original thesis. It is an ill.u.s.tration of a common experience--the explanation of an unimportant action involving principles the most influential considered as a part of Nature's resources.

The address on _The Latent Image_ deals with a subject which had been approached by various writers before the time of my essay; but, so far as I know, an explanation

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based on the facts of photo-electricity had not been attempted.

Students of this subject will notice that the views expressed are similar to those subsequently put forward by Lenard and Saeland in explanation of phosph.o.r.escence. The whole matter is of more practical importance than appears at first sight, for the photoelectric nature of the effects involved in the radiative treatment of many cruel diseases seems to be beyond doubt.

It was in connection with photo-electric science that I was led to take an interest in the application of radioactivity in medicine. The lecture on _The Use of Radium in Medicine_ deals with this subject. Towards the conclusion of this essay reference will be found to a practical outcome of such studies which, by improving on the methods, and facilitating the application, of radioactive treatment, has, in the hands of skilled medical men, already resulted in the alleviation of suffering.

Leaving out much which might well appear in a prefatory notice, a word should yet be added respecting the ill.u.s.trations of scenery.

They are a small selection from a considerable number of photographs taken during my summer wanderings in the Alps in company with Henry H. Dixon. An exception is Plate X, which is by the late Dr. Edward Stapleton. From what has been said above, it will be gathered that these ill.u.s.trations are fitly included among pages which owe so much to Alpine inspiration. They ill.u.s.trate the

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subjects dealt with, and, it is to be hoped, they will in some cases recall to the reader scenes which have in past times influenced his thoughts in the same manner; scenes which in their endless perspective seem to reduce to their proper insignificance the lesser things of life.

My thanks are due to Mr. John Murray for kindly consenting to the reissue of the essay on _The Birth-time of the World_ from the pages of _Science Progress_; to Messrs. Constable & Co. for leave to reprint _Pleochroic Haloes_ from _Bedrock_, and also to make some extracts from _Radioactivity and Geology_; and to the Council of the Royal Dublin Society for permission to republish certain papers from the Proceedings of the Society.

_Iveagh Geological Laboratory, Trinity College, Dublin._

July, 1915.

THE BIRTH-TIME OF THE WORLD [1]

LONG ago Lucretius wrote: "For lack of power to solve the question troubles the mind with doubts, whether there was ever a birth-time of the world and whether likewise there is to be any end." "And if" (he says in answer) "there was no birth-time of earth and heaven and they have been from everlasting, why before the Theban war and the destruction of Troy have not other poets as well sung other themes? Whither have so many deeds of men so often pa.s.sed away, why live they nowhere embodied in lasting records of fame? The truth methinks is that the sum has but a recent date, and the nature of the world is new and has but lately had its commencement."[2]

Thus spake Lucretius nearly 2,000 years ago. Since then we have attained another standpoint and found very different limitations.

To Lucretius the world commenced with man, and the answer he would give to his questions was in accord with his philosophy: he would date the birth-time of the world from the time when

[1] A lecture delivered before the Royal Dublin Society, February 6th, 1914. _Science Progress_, vol. ix., p. 37

[2] _De Rerum Natura_, translated by H. A. J. Munro (Cambridge, 1886).

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poets first sang upon the earth. Modern Science has along with the theory that the Earth dated its beginning with the advent of man, swept utterly away this beautiful imagining. We can, indeed, find no beginning of the world. We trace back events and come to barriers which close our vista--barriers which, for all we know, may for ever close it. They stand like the gates of ivory and of horn; portals from which only dreams proceed; and Science cannot as yet say of this or that dream if it proceeds from the gate of horn or from that of ivory.

In short, of the Earth's origin we have no certain knowledge; nor can we a.s.sign any date to it. Possibly its formation was an event so gradual that the beginning was spread over immense periods. We can only trace the history back to certain events which may with considerable certainty be regarded as ushering in our geological era.

Notwithstanding our limitations, the date of the birth-time of our geological era is the most important date in Science. For in taking into our minds the s.p.a.cious history of the universe, the world's age must play the part of time-unit upon which all our conceptions depend. If we date the geological history of the Earth by thousands of years, as did our forerunners, we must shape our ideas of planetary time accordingly; and the duration of our solar system, and of the heavens, becomes comparable with that of the dynasties of ancient nations. If by millions of years, the sun and stars are proportionately venerable. If by hundreds or thousands of millions of

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years the human mind must consent to correspondingly vast epochs for the duration of material changes. The geological age plays the same part in our views of the duration of the universe as the Earth's...o...b..tal radius does in our views of the immensity of s.p.a.ce. Lucretius knew nothing of our time-unit: his unit was the life of a man. So also he knew nothing of our s.p.a.ce-unit, and he marvels that so small a body as the sun can shed so much, heat and light upon the Earth.

A study of the rocks shows us that the world was not always what it now is and long has been. We live in an epoch of denudation.

The rains and frosts disintegrate the hills; and the rivers roll to the sea the finely divided particles into which they have been resolved; as well as the salts which have been leached from them.

The sediments collect near the coasts of the continents; the dissolved matter mingles with the general ocean. The geologist has measured and mapped these deposits and traced them back into the past, layer by layer. He finds them ever the same; sandstones, slates, limestones, etc. But one thing is not the same. _Life_ grows ever less diversified in character as the sediments are traced downwards. Mammals and birds, reptiles, amphibians, fishes, die out successively in the past; and barren sediments ultimately succeed, leaving the first beginnings of life undecipherable. Beneath these barren sediments lie rocks collectively differing in character from those above: mainly volcanic or poured out from fissures in

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the early crust of the Earth. Sediments are scarce among these materials.[1]

There can be little doubt that in this underlying floor of igneous and metamorphic rocks we have reached those surface materials of the earth which existed before the long epoch of sedimentation began, and before the seas came into being. They formed the floor of a vaporised ocean upon which the waters condensed here and there from the hot and heavy atmosphere. Such were the probable conditions which preceded the birth-time of the ocean and of our era of life and its evolution.

It is from this epoch we date our geological age. Our next purpose is to consider how long ago, measured in years, that birth-time was.

That the geological age of the Earth is very great appears from what we have already reviewed. The sediments of the past are many miles in collective thickness: yet the feeble silt of the rivers built them all from base to summit. They have been uplifted from the seas and piled into mountains by movements so slow that during all the time man has been upon the Earth but little change would have been visible. The mountains have again been worn down into the ocean by denudation and again younger mountains built out of their redeposited materials. The contemplation of such vast events