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Volume 4, 1871
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Notes on Sir William Thomson's Hypothesis that the Germ of Life is derived from Meteors.

3. The President then read the following notes by Mr. Martin Chapman, “On Sir William Thomson's Hypothesis that the Germ of Life is derived from Meteors”:—

I enclose a report of a speech made by Sir William Thomson, President of the British Association, at Edinburgh. I send it on account of the theory there propounded of the advent of organic life on our planet. At first sight it struck me as being, to say the least, attractive; but on further consideration I came to the conclusion that Sir William had not considered the subject very fully. My objections to the theory, or rather hypothesis, are as follows:—

1. Assuming the meteorites which reach the earth to have been planets or

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fragments of planets having organisms, it must be clear that any atmosphere which these little planets might possess must be of a density proportioned to the attraction of the planets themselves, as we know that the density of our atmosphere is due to the weight or gravitation of the atmospheric column, which is in direct proportion to the attractive energy of the earth, and when you diminish the attraction by ascending a high mountain, you find, in about four miles or less, that the density is reduced one-half. Now, as the attraction exercised by a mass, even 100 miles in diameter, would be thousands of times less than that of the earth, even at a distance of four miles from its surface, such a planet would have an atmosphere more rare than the most perfect artificial vacuum capable of being produced by the air pump; and even if such small masses had organisms capable of existence in such a highly attenuated atmosphere, they would be incapable of enduring our atmosphere. But the meteors which reach our earth are to be measured by inches, or at the most by feet, and weighed by pounds. So that their atmospheres (if any) would only be an infinitesimal degree denser than interstellar space. How then can we conceive that any organism capable of living in such an atmosphere could survive when plunged suddenly in our dense atmosphere?

2. These little planets (assuming them to be such) all move in an orbit round the sun, which crosses or approximates to that of the earth; the velocity with which they move (the so-called planetary velocity) is infinitely greater than that of a cannon ball; the necessary result is that the instant they enter our atmosphere, they take fire with such energy that in a few seconds the smaller ones are dissipated into vapour, which, condensing, falls gently to the earth—the so-called cosmical dust, which, I believe, is always to be found in our air; (see “Tyndall on Heat.”) It is only the larger ones which reach the earth in a tangible shape, and you know how very rare they are. They are always in a state of intense heat, indeed, of fusion. Now, what chance would any organism (even the mythical salamander) have of surviving such a conflagration?

3. The third objection which I take is, I think, as strong as any. The hypothesis only shirks the question how organic life began, by attempting to conceal it by substituting the question how organic life arrived on this earth. If organic life existed on these little planets (which according to Sir William have once been portions of some larger planet destroyed by a cataclysm) it must have had a beginning somewhere; and if it began on these planets, where, as far as we can see, the conditions of life would be less favourable than here, why should not organic life also begin on our planet? If the Creator created by direct act, why should not that act have been done on this planet, as well as on others? If, on the other hand, the Creator created by establishing laws, by the operation of which life was gradually evolved from matter,

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again the question suggests itself, why should such beneficial laws not come into operation on this planet, as well as on others? I should not be surprised if this hypothesis were to generate a considerable amount of controversial writing and discussion before very long. I therefore give you my views at once, without being influenced by those of any others. I only hope that they will not prove tedious to you.

After reading that portion of Sir William Thomson's address which contains the hypothesis criticised, Mr. Webb suggested that though some of Mr. Chapman's remarks would undoubtedly apply to organised beings of even a comparatively low type, it was evident that these were not the forms of life Sir William Thomson had in view. It was impossible to say how little such forms as the globigerinæ of the Atlantic depths might be affected by the conditions existing on a meteoric mass. The fact that many aerolites exhibited but very slight traces of surface vitrification showed that the heat to which they had been subjected could not have been very excessive. He adduced other considerations leading to the same conclusion. Evidently Sir William Thomson, who was a firm supporter of the doctrine that the earth had once been a molten mass, had thought this hypothesis necessary to explain the first appearance of life on our planet after it had cooled down to a habitable condition.