The New Astronomy contemplates a period when each of the planets was a germinal nucleus of matter around which other matter was precipitated, thus producing a kind of world-growth or accretion. Thus, for instance, our earth may be considered at a time when its entire mass would not, according to our measurement, have weighed a hundred pounds! It consisted of a nucleus around which extended, through a great space, a mass of attenuated planetary matter. The nucleus once formed the matter adjacent would precipitate itself by gravitation upon the surface of the incipient world. The precipitation would proceed as heat was given off into space. It was virtually a process of condensation; but the result appeared like growth.
To the senses a planet would seem to be forming itself by accretion; and so, indeed, in one sense it was; for the mass constantly increased. As the nucleus sped on in the prescribed pathway, it drew to itself the surrounding matter, leaving behind it an open channel. The orbit was thus cleared of the matter, which was at first merely nebular, and afterward both nebular and fragmentary. The growth at the first was rapid. With each revolution a larger band of space was swept clear of its material. With each passage of the forming globe the matter from the adjacent spaces would rush down upon its surface, and as the mass of the planet increased the process would be stimulated; for gravitation is proportional to the mass. At length a great tubular space would be formed, having the orbit of the earth for its centre, and in this space the matter was all swept up. The tube enlarged with each revolution, until an open way was cut through the nebular disc, and then from the one side toward Venus and from the other side toward Mars the space widened and widened, until the globe took approximately by growth its present mass of matter. The nebulous material was drawn out of the inter-planetary space where it was floating, and the shower of star dust on the surface of the earth became thinner and less frequent. In some parts of the orbit bands or patches of this material existed, and the earth in passing through such hands drew down upon itself the flying fragments of such matter as it continues to do to the present day. What are meteoric displays but the residue of the primordial showers by which the world was formed?
All this work, according to the New Astronomy, took place while our globe was still in a superheated condition. The mass of it had not yet settled into permanent form. The water had not yet become water; it was steam. The metals had not yet become metals; they were rather the vapor of metals. At length they were the liquids of metals, and at last the solids. So, also, the rocks were transformed from the vaporous through the liquid into the solid form—all this while the globe was in process of condensation. It grew smaller in mathematical measurements at the same time that it grew heavier by the accretion of matter. At last the surface was formed, and in time that surface was sufficiently cooled to allow the vapors around it to condense into seas and oceans and rivers. There were ages of superficial softness—vast epochs of mud—in which the living beings that had now appeared wallowed and sprawled.
We cannot trace the world-growth through all its stages but can only indicate them as it were in a sketch. The more important thing to be noted is the relation of our planet in process of formation to the great fact called life. Here the New Astronomy comes in again to indicate, theoretically at least, the philosophy of planetary evolution. Each planet seems to pass through a vast almost inconceivable period in which its condition renders life on its surface or in its structure impossible. Heat is at once the favoring and the prohibitory condition of life. Without heat life cannot exist; with too great heat life cannot exist. With an intermediate and moderate degree of heat many forms of animate and inanimate existence may be promoted.
These facts tend to show that every world has in its career an intermediate period which may be called the epoch of life. Before the epoch of life begins there is in the given world no such form of existence. There is matter only. Then at a certain stage the epoch of life begins. The epoch of life continues for a vast indeterminate period. No doubt in some of the worlds an epoch of life has been provided ten times as great, possibly a thousand times as great, as in other planets. After the epoch of life begins only certain forms of existence are for a while possible. Then other and higher forms succeed them, and then still higher. Thus the process continues until the highest—that is, the conscious and moral form of existence becomes possible, and that highest, that conscious, that moral form of being is ourselves.
This is not all. The epoch of life seems to be terminable at the further extreme by a planetary condition in which life is no longer possible. The New Astronomy indicates the coming of a condition in all the worlds when life must disappear therefrom and be succeeded by a lifeless state of worldhood. This may be called the epoch of death—that is, of world-death. It seems to be almost established by investigation and right reason that worlds die. They reach a stage in which they are lifeless. They cool down until the waters and gases that are on the surface and above the surface recede more and more into the surface and then into the interior, until they wholly disappear. Cold takes the throne of nature. Universal aridity supervenes, and all forms of vegetable and animate existence go away to return no more. They dwindle and expire. The conditions that have come are virtually conditions of death.
Whether the universe contains within itself, under the Almighty supervision, certain arrangements and laws by which the dead world can be again cast into the crucible and regenerated by liberation through the action of heat into its primordial state once more and go the same tremendous round of planet life, we know not. The conception of such a process, even the dream or vague possibility of it, is sufficiently sublime and fills the mind with a great delight in contemplating the possible cycles through which the material universe is passing.
At any rate, we may contemplate the three great stages of world-life with which we are already acquainted—that is, the birth stage, the epoch of life and the epoch of death. There is a birth, as also a life and a death of planets. Richard A. Proctor, of great fame, on one of his last tours of instructive lecturing among our people, had for his subject the "Birth and Death of Worlds." The theme was not dissimilar to that which has been here presented in outline. The birth, the life and the death of worlds! Such is a summary of that almost infinite history through which our earth is passing—the history which the globe is making on its way from its nebulous to its final state.
Such, if we mistake not, is the story epitomized—the life history in brief—of all the worlds of space. They have each in its order and kind, an epoch of the beginning, then an epoch of growth and evolution, then an epoch of life—toward which all the preceding planet history seems to tend—and finally an epoch of death which must, in the course of infinite time, swallow from sight each planet in its turn, or at least reduce each from that condition in which it is an arena of animated existence into that state where it is a frozen and desert clod, still following its wonted path through space, still shining with a cold but cheerful face, like our moon, upon the silent abysses of the universe.