"On The Secular Cooling Of The Earth" By Lord Kelvin (William Thomson)

Excerpt. Transactions of the Royal Society of Edinburgh, Vol. XX111 (1864), pp. 167-169


8. It must indeed be admitted that many geological writers of the "Uniformitarian"

school, who in other respects have taken a profoundly philosophical view of their

subject, have argued in a most fallacious manner against hypotheses of violent

action in past ages. If they had contented themselves with showing that many

existing appearances, although suggestive of extreme violence and sudden

change, may have been brought about by long-continued action, or by paroxysms

not more intense than some of which we have experience within the periods of

human history, their position might have been unassailable; and certainly could

not have been assailed except by a detailed discussion of their facts. It would be a

very wonderful, but not an absolutely incredible result, that volcanic action has

never been more violent on the whole than during the last two or three centuries;

but it is as certain that there is now less volcanic energy in the whole earth than

there was a thousand years ago, as it is that there is less gunpowder in a

"Monitor" after she has been seen to discharge shot and shell, whether at a nearly

equable rate or not, for five hours without receiving fresh supplies, than there was

at the beginning of the action. Yet this truth has been ignored or denied by many

of the leading geologists of the present day, because they believe that the facts

within their province do not demonstrate greater violence in ancient changes of

the earth's surface, or do demonstrate a nearly equable action in all periods.


9. The chemical hypothesis to account for underground heat might be regarded as

not improbable, if it was only in isolated localities that the temperature was found

to increase with the depth; . . . but that there is slow uniform "combustion," . . . or

chemical combination of any kind going on, at some great unknown depth under

the surface everywhere, and creeping inwards gradually as the chemical affinities

in layer after layer are successively saturated, seems extremely improbable,

although it cannot be pronounced to be absolutely impossible, or contrary to all

analogies in nature. The less hypothetical view, however, that the earth is merely

a warm chemically inert body cooling, is clearly to be preferred in the present

state of science.


10. Poisson's celebrated hypothesis, that the present underground heat is due to a

passage, at some former period, of the solar system through hotter stellar regions,

cannot provide the circumstances required for a palaeontology continuous through

that epoch of external heat. For from a mean of values of the conductivity, in

terms of the thermal capacity of unit volume, of the earth's crust, in three

different localities near Edinburgh, which I have deduced from the observations on

underground temperature instituted by Principal Forbes there, I find that if the

supposed transit through a hotter region of space took place between 1250 and

5000 years ago, the temperature of that supposed region must have been from

25° to 50° Fahr. above the present mean temperature of the earth's surface, to

account for the present general rate of underground increase of temperature,

taken as 1° Fahr. in 50 feet downwards. Human history negatives this supposition.

Again, geologists and astronomers will, I presume, admit that the earth cannot,

20,000 years ago, have been in a region of space 100° Fahr. warmer than its

present surface. But if the transition from a hot region to a cool region supposed

by Poisson took place more than 20,000 years ago, the excess of temperature

must have been more than 100° Fahr., and must therefore have destroyed animal

and vegetable life. Hence, the farther back and the hotter we can suppose

Poisson's hot region, the better for the geologists who require the longest periods;

but the best for their view is Leibnitz's theory, which simply supposes the earth to

have been at one time an incandescent liquid, without explaining how it got into

that state. If we suppose the temperature of melting rock to be about 10,000°

Fahr. (an extremely high estimate), the consolidation may have taken place

200,000,000 years ago. Or, if we suppose the temperature of melting rock to be

7000° Fahr. (which is more nearly what it is generally assumed to be), we may

suppose the consolidation to have taken place 98,000,000 years ago.


11. . . . But we are very ignorant as to the effects of high temperatures in altering

the conductivities and specific heats of rocks, and as to their latent heat of fusions. We

must, therefore, allow very wide limits in such an estimate as I have attempted to make; but

I think we may with much probability say that the consolidation cannot have taken

place less than 20,000,000 years ago, or we should have more underground heat

than we actually have, nor more than 400,000,000 years ago, or we should not

have so much as the least observed underground increment of temperature. That

is to say, I conclude that Leibnitz's epoch of "emergence" of the "consistentior

status" [i.e. solid earth (ed. note)] was probably between those dates.

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"Address of Sir William Thomson, Knt., LL.D., F.R.S, President" [Lord Kelvin]

Excerpt on the origin of life on earth. Report of the Forty-First Meeting of the British Association for the Advancement of Science; held at Edinburgh in August 1871, pages lxxxiv-cv


The essence of science, as is well illustrated by astronomy and cosmical

physics, consists in inferring antecedent conditions, and anticipating further evolutions,

from phenomena which have actually come under observation. In biology the

difficulties of successfully acting up to this ideal are prodigious. The earnest

naturalists of the present day are, however, not appalled or paralyzed by them,

and are struggling boldly and laboriously to pass out of the mere 'Natural History

stage' of their study, and bring zoology within the range of Natural Philosophy. A

very ancient speculation, still clung to by many naturalists (so much so that I have

a choice of modern terms to quote in expressing it), supposes that, under

meteorological conditions very different from the present, dead matter may have

run together or crystallized or fermented into 'germs of life,' or 'organic cells,' or

'protoplasm.' But science brings a vast mass of inductive evidence against this

hypothesis of spontaneous generation, as you have heard from my predecessor in

the Presidential chair. Careful enough scrutiny has, in every case up to the

present day, discovered life as antecedent to life. Dead matter cannot become

living without coming under the influence of matter previously alive. This seems to

me as sure a teaching of science as the law of gravitation. I utterly repudiate, as

opposed to all philosophical uniformitarianism, the assumption of 'different

meteorological conditions'—that is to say, somewhat different vicissitudes of

temperature, pressure, moisture, gaseous atmosphere—to produce or to permit

that to take place by force or motion of dead matter alone, which is a direct

contravention of what seems to us biological law. I am prepared for the answer,

'our code of biological law is an expression of our ignorance as well as of our

knowledge.' And I say yes: search for spontaneous generation out of inorganic

materials; let any one not satisfied with the purely negative testimony, of which

we have now so much against it, throw himself into the inquiry. Such

investigations as those of Pasteur, Pouchet, and Bastian are among the most

interesting and momentous in the whole range of Natural History, and their

results, whether positive or negative, must richly reward the most careful and

laborious experimenting. I confess to being deeply impressed by the evidence put

before us by Professor Huxley, and I am ready to adopt, as an article of scientific

faith, true through all space and through all time, that life proceeds from life, and

from nothing but life.

How, then, did life originate on the Earth? Tracing the physical history of the

Earth backwards, on strict dynamical principles, we are brought to a red-hot melted

globe on which no life could exist. Hence when the Earth was first fit for life, there

was no living thing on it. There were rocks solid and disintegrated, water, air all

round, warmed and illuminated by a brilliant Sun, ready to become a garden. Did

grass and trees and flowers spring into existence, in all the fullness of ripe beauty,

by a fiat of Creative Power? or did vegetation, growing up from seed sown, spread

and multiply over the whole Earth? Science is bound, by the everlasting vow of

honour, to face fearlessly every problem which can be fairly presented to it. If a

probable solution, consistent with the ordinary course of nature, can be found, we

must not invoke an abnormal act of Creative Power. When a lava stream flows

down the sides of Vesuvius or Etna it quickly cools and becomes solid; and after a

few weeks or years it teems with vegetable and animal life, which for it originated

by the transport of seed and ova and by the migration of individual living

creatures. When a volcanic island springs up from the sea, and after a few years is

found clothed with vegetation, we do not hesitate to assume that seed has been

wafted to it through the air, or floated to it on rafts. Is it not possible, and if

possible, is it not probable, that the beginning of vegetable life on the Earth is to

be similarly explained? Every year thousands, probably millions, of fragments of

solid matter fall upon the Earth—whence came these fragments? What is the

previous history of any one of them? Was it created in the beginning of time an

amorphous mass? This idea is so unacceptable that, tacitly or explicitly, all men

reject it. It is often assumed that all, and it is certain that some, meteoric stones

are fragments which had been broken off from greater masses and launched free

into space. It is as sure that collisions must occur between great masses moving

through space as it is that ships, steered without intelligence directed to prevent

collision, could not cross and recross the Atlantic for thousands of years with

immunity from collisions. When two great masses come into collision in space it is

certain that a large part of each is melted; but it seems also quite certain that in

many cases a large quantity of debris must be shot forth in all directions, much of

which may have experienced no greater violence than individual pieces of rock

experience in a land-slip or in blasting by gunpowder. Should the time when this

earth comes into collision with another body, comparable in dimensions to itself,

be when it is still clothed as at present with vegetation, many great and small

fragments carrying seed and living plants and animals would undoubtedly be

scattered through space. Hence and because we all confidently believe that there

are at present, and have been from time immemorial, many worlds of life besides

our own, we must regard it as probable in the highest degree that there are

countless seed-bearing meteoric stones moving about through space. If at the

present instant no life existed upon this earth, one such stone falling upon it

might, by what we blindly call natural causes, lead to its becoming covered with

vegetation. I am fully conscious of the many scientific objections which may be

urged against this hypothesis; but I believe them to be all answerable. I have

already taxed your patience too severely to allow me to think of discussing any of

them on the present occasion. The hypothesis that life originated on this earth

through moss-grown fragments from the ruins of another world may seem wild

and visionary; all I maintain is that it is not unscientific.

From the Earth stocked with such vegetation as it could receive meteorically,

to the Earth teeming with all the endless variety of plants and animals which now

inhabit it, the step is prodigious; yet, according to the doctrine of continuity, most

ably laid before the Association by a predecessor in this Chair (Mr. Grove), all

creatures now living on earth have proceeded by orderly evolution from some such

origin. Darwin concludes his great work on `The Origin of Species' with the

following words:—'It is interesting to contemplate an entangled bank clothed with

many plants of many kinds, with birds singing on the bushes, with various insects

flitting about, and with worms crawling through the damp earth, and to reflect that

these elaborately constructed forms, so different from each other, and dependent

on each other in so complex a manner, have all been produced by laws acting

around us.' . . . . 'There is grandeur in this view of life with its several powers,

having been originally breathed by the Creator into a few forms or one; and that,

whilst this planet has gone cycling on according to the fixed law of gravity, from so

simple a beginning endless forms, most beautiful and most wonderful, have been

and are being evolved.' With the feeling expressed in these two sentences I most

cordially sympathize. I have omitted two sentences which come between them,

describing briefly the hypothesis of 'the origin of species by natural selection,'

because I have always felt that this hypothesis does not contain the true theory of

evolution, if evolution there has been, in biology. Sir John Herschel, in expressing

a favourable judgment on the hypothesis of zoological evolution (with, however,

some reservation in respect to the origin of man), objected to the doctrine of

natural selection, that it was too like the Laputan method of making books, and

that it did not sufficiently take into account a continually guiding and controlling

intelligence. This seems to me a most valuable and instructive criticism. I feel

profoundly convinced that the argument of design has been greatly too much lost

sight of in recent zoological speculations. Reaction against the frivolities of

teleology, such as are to be found, not rarely, in the notes of the learned

commentators on Paley's 'Natural Theology,' has I believe had a temporary effect

in turning attention from the solid and irrefragable argument so well put forward

in that excellent old book. But overpoweringly strong proofs of intelligent and

benevolent design lie all around us; and if ever perplexities, whether metaphysical

or scientific, turn us away from them for a time, they come back upon us with

irresistible force, showing to us through Nature the influence of a free will, and

teaching us that all living things depend on one ever-acting Creator and Ruler.

[p. ciii-cv]

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