The Birth-Time of the World and Other Scientific Essays

John Joly

The Birth-Time of the World and Other Scientific Essays

EAN 8596547136941

DigiCat, 2022

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Table of Contents

PREFACE

THE BIRTH-TIME OF THE WORLD [1]

DENUDATION

THE ABUNDANCE OF LIFE [1]

THE BRIGHT COLOURS OF ALPINE FLOWERS [1]

MOUNTAIN GENESIS

ALPINE STRUCTURE

OTHER MINDS THAN OURS?

THE LATENT IMAGE [1]

PLEOCHROIC HALOES [1]

THE USE OF RADIUM IN MEDICINE [1]

SKATING [1]

A SPECULATION AS TO A PREMATERIAL UNIVERSE [1]

INDEX

"

PREFACE

Table of Contents

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

xi

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 accumulation 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

assumption 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 accumulation of wrinkling which we term mountain

chains. The

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

xii

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 entitled _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 attitude of the organism

towards energy external to it; an attitude which results in its

evasion of the retardative 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 canals. 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

xiii

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 accumulated since remote

geological times, and assuring us, indirectly, of the stability

of the chemical elements in general since the beginning of the

world. This assurance is, without proof, often assumed 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 illustration 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

xiv

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 phosphorescence. 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 illustrations 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 illustrations are fitly included

among pages which owe so much to Alpine inspiration. They

illustrate the

xv

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.

xvi

THE BIRTH-TIME OF THE WORLD [1]

Table of Contents

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 passed 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).

1

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 assign 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 spacious 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

2

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 orbital radius does in our views of the immensity of

space. Lucretius knew nothing of our time-unit: his unit was the

life of a man. So also he knew nothing of our space-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

3

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

[1] For a description of these early rocks, see especially the

monograph of Van Hise and Leith on the pre-Cambrian Geology of

North America (Bulletin 360, U.S. Geol. Survey).

4

prepares our minds to accept many scores of millions of years or

hundreds of millions of years, if such be yielded by our

calculations.

THE AGE AS INFERRED FROM THE THICKNESS OF THE SEDIMENTS

The earliest recognised method of arriving at an estimate of the

Earth's geological age is based upon the measurement of the

collective sediments of geological periods. The method has

undergone much revision from time to time. Let us briefly review

it on the latest data.

The method consists in measuring the depths of all the successive

sedimentary deposits where these are best developed. We go all

over the explored world, recognising the successive deposits by

their fossils and by their stratigraphical relations, measuring

their thickness and selecting as part of the data required those

beds which we believe to most completely represent each

formation. The total of these measurements would tell us the age

of the Earth if their tale was indeed complete, and if we knew

the average rate at which they have been deposited. We soon,

however, find difficulties in arriving at the quantities we

require. Thus it is not easy to measure the real thickness of a

deposit. It may be folded back upon itself, and so we may measure

it twice over. We may exaggerate its thickness by measuring it

not quite straight across the bedding or by unwittingly including

volcanic materials. On the other hand, there

5

may be deposits which are inaccessible to us; or, again, an

entire absence of deposits; either because not laid down in the

areas we examine, or, if laid down, again washed into the sea.

These sources of error in part neutralise one another. Some make

our resulting age too long, others make it out too short. But we

do not know if a balance of error does not still remain. Here,

however, is a table of deposits which summarises a great deal of

our knowledge of the thickness of the stratigraphical

accumulations. It is due to Sollas.[1]

Feet.

Recent and Pleistocene - - 4,000

Pliocene - - 13,000

Miocene - - 14,000

Oligocene - - 2,000

Eocene - - 20,000

63,000

Upper Cretaceous - - 24,000

Lower Cretaceous - - 20,000

Jurassic - - 8,000

Trias - - 7,000

69,000

Permian - - 2,000

Carboniferous - - 29,000

Devonian - - 22,000

63,000

Silurian - - 15,000

Ordovician - - 17,000

Cambrian - - 6,000

58,000

Algonkian—Keeweenawan - - 50,000

Algonkian—Animikian - - 14,000

Algonkian—Huronian - - 18,000

82,000

Archæan - - ?

Total - - 335,000 feet.

[1] Address to the Geol. Soc. of London, 1509.

6

In the next place we require to know the average rate at which

these rocks were laid down. This is really the weakest link in

the chain. The most diverse results have been arrived at, which

space does not permit us to consider. The value required is most

difficult to determine, for it is different for the different

classes of material, and varies from river to river according to

the conditions of discharge to the sea. We may probably take it

as between two and six inches in a century.

Now the total depth of the sediments as we see is about 335,000

feet (or 64 miles), and if we take the rate of collecting as

three inches in a hundred years we get the time for all to

collect as 134 millions of years. If the rate be four inches, the

time is soo millions of years, which is the figure Geikie

favoured, although his result was based on somewhat different

data. Sollas most recently finds 80 millions of years.[1]

THE AGE AS INFERRED FROM THE MASS OF THE SEDIMENTS

In the above method we obtain our result by the measurement of

the linear dimensions of the sediments. These measurements, as we

have seen, are difficult to arrive at. We may, however, proceed

by measurements of the mass of the sediments, and then the method

becomes more definite. The new method is pursued as follows:

[1] Geikie, _Text Book of Geology_ (Macmillan, 1903), vol. i., p.

73, _et seq._ Sollas, _loc. cit._ Joly, _Radioactivity and Geology_

(Constable, 1909), and Phil. Mag., Sept. 1911.

7

The total mass of the sediments formed since denudation began may

be ascertained with comparative accuracy by a study of the

chemical composition of the waters of the ocean. The salts in the

ocean are undoubtedly derived from the rocks; increasing age by

age as the latter are degraded from their original character

under the action of the weather, etc., and converted to the

sedimentary form. By comparing the average chemical composition

of these two classes of material—the primary or igneous rocks and

the sedimentary—it is easy to arrive at a knowledge of how much

of this or that constituent was given to the ocean by each ton of

primary rock which was denuded to the sedimentary form. This,

however, will not assist us to our object unless the ocean has

retained the salts shed into it. It has not generally done so. In

the case of every substance but one the ocean continually gives

up again more or less of the salts supplied to it by the rivers.

The one exception is the element sodium. The great solubility of

its salts has protected it from abstraction, and it has gone on

collecting during geological time, practically in its entirety.

This gives us the clue to the denudative history of the

Earth.[1]

The process is now simple. We estimate by chemical examination of

igneous and sedimentary rocks the amount of sodium which has been

supplied to the ocean per ton of sediment produced by denudation.

We also calculate

[1] _Trans. R.D.S._, May, 1899.

8

the amount of sodium contained in the ocean. We divide the one

into the other (stated, of course, in the same units of mass),

and the quotient gives us the number of tons of sediment. The

most recent estimate of the sediments made in this manner affords

56 x 10¹⁶ tonnes.[1]

Now we are assured that all this sediment was transported by the

rivers to the sea during geological time. Thus it follows that,

if we can estimate the average annual rate of the river supply of

sediments to the ocean over the past, we can calculate the

required age. The land surface is at present largely covered with

the sedimentary rocks themselves. Sediment derived from these

rocks must be regarded as, for the most part, purely cyclical;

that is, circulating from the sea to the land and back again. It

does not go to increase the great body of detrital deposits. We

cannot, therefore, take the present river supply of sediment as

representing that obtaining over the long past. If the land was

all covered still with primary rocks we might do so. It has been

estimated that about 25 per cent. of the existing continental

area is covered with archæan and igneous rocks, the remainder

being sediments.[2] On this estimate we may find valuable

[1] Clarke, _A Preliminary Study of Chemical Denudation_

(Washington, 1910). My own estimate in 1899 (_loc. cit._) made as a

test of yet another method of finding the age, showed that the

sediments may be taken as sufficient to form a layer 1.1 mile

deep if spread uniformly over the continents; and would amount to

64 x 10¹⁸ tons.

[2] Van Tillo, _Comptes Rendues_ (Paris), vol. cxiv., 1892.

9

major and minor limits to the geological age. If we take 25 per

cent. only of the present river supply of sediment, we evidently

fix a major limit to the age, for it is certain that over the

past there must have been on the average a faster supply. If we

take the entire river supply, on similar reasoning we have what

is undoubtedly a minor limit to the age.

The river supply of detrital sediment has not been very

extensively investigated, although the quantities involved may be

found with comparative ease and accuracy. The following table

embodies the results obtained for some of the leading rivers.[1]

Mean annual Total annual Ratio of

discharge in sediment in sediment

cubic feet thousands to water

per second. of tons. by weight.

Potomac - 20,160 5,557 1 : 3.575

Mississippi - 610,000 406,250 1 : 1,500

Rio Grande - 1,700 3,830 1 : 291

Uruguay - 150,000 14,782 1 : 10,000

Rhone - 65,850 36,000 1 : 1,775

Po - 62,200 67,000 1 : 900

Danube - 315,200 108,000 1 : 2,880

Nile - 113,000 54,000 1 : 2,050

Irrawaddy - 475,000 291,430 1 : 1,610

Mean