The Age of the Earth

Abstract

WITH reference to the ingenious suggestion by Mr. Preston, on the earth's orbit having been practically diminished by ethereal retardation, there are a few other points to be considered. 1. That the minor planets could never have passed the major planets, as they would be certainly caught by them during the immense number of revolutions in which their orbits would be nearly equal. Therefore the earth cannot have dropped in from much farther than Jupiter's present orbit; for if during its revolutions it came within one-sixth of the distance from Jupiter that it now is from the sun, it would be mastered by Jupiter. 2. By the retardation of Encke's comet it seems that if the comet had the same orbit as the earth, its distance from the sun would diminish about 1/25000 per year. But for any appreciable lengthening of the earth's life-period, the earth must have started much more than one-tenth farther from the sun than it now is; that is to say, it must fall in much quicker than at the rate of its present distance from the sun in 108 years. This shows that the individual portions of Encke's comet must be much more than two miles in diameter, even supposing it to have as great a mean density as the earth, and to consist of a shower of solid meteors. Thus if the earth's history should be lengthened by any important amount from this cause, the nucleus of Encke's comet must consist of a shower of bodies of as great a density as the earth, and of a considerable size, each weighing very much more than 100,000,000 tons. And considering that there must be thousands of such bodies to compose it, the total mass would be greatly beyond what is considered possible. 3. If the earth had drawn much nearer to the sun, the asteroids must have come in from a very much greater distance; and yet, though they differ greatly in size, they are all grouped closely together, whereas we should find then sorted out very much more widely, and a vast quantity of them retained by Jupiter as satellites.