The Evolution of Worlds

by Percival Lowell

Ideal section of a laccolith—
Gilbert.

Whether our Earth was ever hot enough at the surface to vaporize those substances which now form the Jovian or Saturnian clouds, we do not know; but that it was once hot enough to vaporize water we are perfectly certain. And this from proof both of what did exist and of what did not. That the surface temperature was at onetime in the thousands of degrees Fahrenheit, the Plutonic magma underlying all the sedimentary rocks of the Earth amply shows. Reversely, the absence of any effect of water until we reach these sedimentary deposits, testifies that during all the earlier stages of the Earth’s career water as such was absent, and as water subsequently appeared, it is clear that the conditions did not at first allow it to form. We are sure, therefore, that there was a time when water existed only as steam, and very possibly a period still anterior to that when it did not exist at all, its constituent hydrogen and oxygen not having yet combined. There was certainly an era, then, in the morning of the ages, when the Earth wore her cloud-wrapper much as Jupiter his now.

That the seas were not once and yet are to-day, affords proof positive that at some intermediate period they began to be. Avery long intermediate one it must have been, too,—all the time it took the Earth to cool from about 2000° C. to 100° C. Not till after the temperature had fallen to the latter figure in the outer regions of the atmosphere could clouds form, and not till it had done so at the solid surface could the steam be deposited as water. Reasoning thus presents us with a picture of our Earth as a vast seething caldron from which steam condensing into cloud was precipitated upon a heated layer of rock, to rise in clouds of steam again. The solid surface had by this time formed, thickening slowly and more or less irregularly, and into its larger dimples the water settled as it grew, deepening them into the great ocean basins of to-day. We see the process with as much certainty and considerably more comfort than if, in the French sense, we had assisted at it. Presence of mind now thus amply makes up for absence of body then.

Passing on evolutionarily we reach more and more tolerable conditions and solid ground in fact, as well as theory. Thus the crust hardened and cooled, while the oceans still remained uncomfortably hot. For water requires much more heat to warm it to a given temperature than rock, about four and a half times as much. It has therefore by so much the more to lose, and is proportionally long in the losing. These hot seas must have produced a small universe of cloud, and as the conditions were the same all over the Earth, we can see easily with the mind’s eye that we could not have seen at all with the bodily one, had we occupied the land in those very early days. To be quite shut out from curious sight without, was hardly made up for by not being able to see more than dimly within. Any one who has stood on the edge of a not-extinct crater when the wind was blowing his way, will have as good a realization of the then state of things as he probably cares for.

Now this astronomic drawing of the then Earth, which by its lack of detail allows of no doubt whatever, permits us to offer help in the elucidation of some of their phenomena to our geologic colleagues. We are the more emboldened to do so in that they have themselves appealed to astronomy for diagnosis, and accepted nostrums devised by themselves. It is always better in such cases to call in a regular practitioner. Not that he is necessarily more astute, but that he knows what will not work. It was in the matter of the paleologic climate that they were led to consult astronomy. The singular thing about paleologic times was the combination of much warmth with little light; and the not less singular fact that these conditions were roughly uniform over the whole Earth. From this universality it was clear, as De Lapparent, their chief spokesman, puts it, that nothing local could explain the fact. It was something which demanded a cause common to the globe.

It thus fell properly within the province of astronomy. For if we are to draw any line between the spheres of influence of the two sciences, it would seem to lie where totality ends and provincialism begins. I use this not as a pejorative, but simply to part local color from one universal drab. In the Earth’s general attributes,—its size, shape, and weight,—we must have recourse to astronomy to learn the facts. Not less so for those principal causes which have shaped its general career; we surrender it only at the point where everyday interest begins, when those causes that led it through its uninviting youth give way to effects which in the least concern humanity at large.

Between the mere aggregation of matter into planetary bodies, of which nebular hypotheses treat, and the specific transformation of plants and animals upon their surfaces with which organic evolution is concerned, lies a long history of development, which, beginning at the time the body starts to cool, continues till it become, for one cause or another, again an inert mass. In this period is contained its career as a world. Planetology I have ventured to call the brand of astronomy which deals with this evolution of worlds. It treats of what is general and cosmic in that evolution, as geology treats of what is terrestrial and specific in the history of one member of the class, our own Earth. The two do not interfere, as the one faces questions in time and space to which the other remains perforce a stranger. If the picture by the one be fuller of detail, the canvas of the other permits of the wider perspective. Certain events in the history of our Earth can only be explained by astronomy, as geologists have long since recognized. It is these that fall into our present province.

Geologists, however, have applied astronomy according to their own ideas. Either they called in aurists, so to speak, when what they needed was an oculist, or they went to books for their drugs, which they then administered themselves—a somewhat dangerous practice. Thus they began by displacing the Earth’s axis in hope of effecting a result; not realizing that this would only shift the trouble, not cure it; in fact, make it rather worse. They next tried what De Lapparent, one of the most brilliant geologists of the age, calls “a variation in the eccentricity of the ecliptic[16] joined to precession of the equinoxes,”—a startling condition unknown to astronomy which does not deal in eccentric planes, whatever such geometric anomalies may be, but by which its coiner evidently means a change in the eccentricity of the orbit, as the context shows. Its effect on the Earth, as he wisely points out, would be to reduce its extremities to extremes. To get out of his quandary he then embraced a brilliant suggestion of a brother geologist, M. Blandet. M. Blandet conceived the idea, and brought it forth unaided, that all that was necessary was a sun big enough to look down on both poles of the Earth at once. To get this he travelled back to the time when, in Laplace’s cosmogony, the Sun filled the whole orbit of Mercury. This conception, which, De Lapparent remarks, “might, at the time of its apparition, have disconcerted spirits accustomed to consider our system as stable,”—an apparition which we may add would certainly continue to disconcert them,—he says seems to him quite in harmony with that system’s genesis. That it labors under two physical impossibilities, one on the score of the Sun, the other on that of the Earth, and that in this case two negatives do not make an affirmative, need not be repeated here, as the reader will find it set forth at length elsewhere,[17] together with what I conceive to be the only explanation of paleothermal times which will work astronomically—presently to be mentioned. But before I do so, it is pertinent to record two things that have come to my notice since. One is that in rereading Faye’s “Origine du Monde,” I came upon a passage in which it appears that M. Blandet had actually consulted Faye about his hypothesis, and that Faye had shown him its impossibility on much the same grounds as those above referred to; which, however, did not deter M. Blandet from giving it to the world nor De Lapparent from god-fathering the conception.

Faye, meanwhile, developed his theory of the origin of the world, and by it explained the greater heat and lesser light of paleologic times compared with our own, thus: The Earth evolved before the Sun. In paleologic times the Sun was still of great extent,—an ungathered-up residue of nebula that had not yet fallen together enough to concentrate, not a contracting mass from which the planets had been detached,—and was in consequence but feebly luminous and of little heating effect; so that there were no seasons on Earth and no climatic zones. The Earth itself supplied the heat felt uniformly over its whole surface.

This differs from my conception, as the reader will see presently, in one vital point—as to why the Earth was not heated by the Sun. In the first place Faye’s sun has no raison d’être; and in the second no visible means of existence. If its matter were not already within the orbit of the Earth at the time, there seems no reason why it should ever get there; and if there, why it should have been so loath to condense. We cannot admit, I think, any such juvenility in the Sun at the time the Earth was already so far advanced as geology shows it to have been in paleologic times. For the Earth had already cooled below the boiling-point of water.