"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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