< Page:Popular Science Monthly Volume 9.djvu
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THE PROBABLE AGE OF THE WORLD.

tion of the prodigious length of time that it must have taken to excavate the gorge? We should certainly feel startled when on making the necessary calculations we found that the stream had performed this enormous amount of work in something less than a million years.

The absolute settlement of the question must ever be above our powers. For a few centuries only we have the comparative daylight of historical times; thence backward lies the rapidly-gathering twilight of tradition; beyond that, geological periods the duration of which can be only vaguely guessed at, and beyond all these, far back in past eternity, the epoch when Time began. The old belief, which limited the existence of the earth to less than seven thousand years, gave way once for all, almost within living memory. All men are now agreed that the six days of creation were periods of indefinite extent. They are not solar days—for evening happened and morning happened three times over before the sun was created. Not being days measured by the sun, we know not how many thousands of years they may have endured. The reaction was sudden and complete. Geology jumped to the conclusion that the past history of the world was without any limits that human imagination could conceive. But in quite recent years, as we have tried to show, the calm light of science has proved that the practical eternity of matter is not more tenable than the arbitrary limitation by which thought was formerly confined.

"I dare say," says Prof. Tait, "that many of you are acquainted with the speculations of Lyell and others, especially of Darwin, who tell us that even for a comparatively brief portion of recent geological history three hundred millions of years will not suffice! We say—so much the worse for geology as at present understood by its chief authorities, for.... physical considerations render it impossible that more than ten or fifteen millions of years can be granted."

Sir William Thomson is not so sweeping in his assertion: but then the nature of the problem before him did not require any such opinion at his hands. His argument aimed at disproving Playfair's assertion that neither the heavenly bodies nor the earth offered any evidence of a beginning, or any advance toward an end. If, therefore, Sir William Thomson was able to show that there was good evidence both of a beginning and an end, he was not concerned to speculate how long past time had existed, or when the end would come. His summing up is this:

"We must admit some limit. . . . Dynamical theory of the sun's heat renders it almost impossible that the earth's surface has been illuminated by the sun many times ten million years. And when finally we consider underground temperature we find ourselves driven to the conclusion that the existing state of things on the earth, life on the earth, and all geological history showing continuity of life, must be limited within some such period of past time as one hundred million years."
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