The Evolution of Worlds/Chapter 6
CHAPTER VI
A PLANET'S HISTORY
Self-sustained Stage
UP to this point in our retrospective survey the long course of evolution has taken one line, that of dynamical separation of the system's parts with subsequent reunitement of them according to the laws of celestial mechanics. Of this action I have submitted the reader my brief: departing in it from common-law practice, in which the cause of action is short and the brief long. And I have, I trust, guarded against his appealing on exceptions.
From this point on we have two kinds of development to follow: the one intrinsic, the chemical; the other incidental, the physical. Not that, in a way, the one is divorcible from the other. For the physical makes possible the chemical by furnishing it the conditions to act. But in another sense, and that which is most thrust upon our notice, the two are independent. Thus oceans and land, hills and valleys, clouds and blue sky, as we know them,—everything, pretty much, which we associate with a world,—are not universal, inevitable, results of planetary evolution, but resultant, individual, characteristics of our particular abode. They are as much our own as the peculiar arithmetic of waiters is theirs, or as used to be the sobriety of the country doctor's horse—his and no other's. Our whole geologic career is essentially earthly. Not that its fundamental laws are not of universal application, but the kaleidoscopic patterns they produce depend on the little idiosyncrasies of the constituents and the mode in which these fall together. Our everyday experiences we should find quite changed, could we alight on Venus or on Mars.
On the other hand, the chemical changes which follow a body's acquisition of heat, setting in the moment that heat has reached its acme and starts to decline, are as universal as the universe itself. They are conditioned, it is true, by the body's size and by the position that body occupied in the primal nebula, but they depend directly upon the degree of heat the body had attained. The larger the planet, the higher the temperature it reached and the fuller its possibilities. Even the planets are born to their estate. Thus the little meteorites live their whole waking life during the few seconds they spend rushing through our air. For then only does change affect their otherwise eternally inert careers. That the time is too short for any important experience is evident on their faces.
Heat is most intimately associated with the very constitution of matter. It is, in fact, merely the motion of its ultimate particles, and plays an essential part in their chemical relations. Just as a certain discreet fervor and sufficient exposure for attraction to take, make for matrimony, so with the little molecules, a suitable degree of warmth and a propitious opportunity similarly conduce to conjunction; too fiery a temperament resulting in a vagabondage preventative of settled partnership and too cold a one in permanent celibacy. You may think the simile a touch too anthropomorphic, but it is a most sober statement of fact. Indeed, it is more than probable that in some dull sense they feel the impulse, though not the need of expressing it in verse. That metals can remember their past states seems to have been demonstrated by Bose, and is certainly in keeping with general principles as we know them to-day. For memory is the partial retention of past changes, rendering those changes more facile of repetition.
A high degree of heat, then, makes chemical union impossible, because the great speeds at which the molecules are rushing past each other prevents any of them being caught. Lack of speed is equally deterrent. Nor is it wholly or even principally, perhaps, a movement of the whole which is here concerned, but a partitive throbbing of the molecule itself. Certain it is that great cold is as prohibitive of chemic combination as great heat. Phosphorus, which evinces such avidity for oxygen at ordinary temperatures as to have got its name from the way it publishes the fact, at very low ones shows a coolness for its affinity amounting to absolute unconcern. Thus only within a certain range of temperature does chemical combination occur. To remain above or below this is to stay forever immortally dead. To get hot enough in the first place, and then subsequently to cool, are therefore essential processes to a body which is to know evolutionary advance.
To pen the history of the solar system and leave out of it all mention of its most transcendentally wonderful result, the chemical evolution attendant upon cooling, would be to play "Hamlet" with Hamlet left out. For the thing which makes the second half of the great cosmic drama so inconceivably grand is the building up of the infinitely little into something far finer than the infinitely great. The mechanical action that first tore a sun apart, and then whirled the fragments into the beautifully symmetric system we behold to-day, is of a grandeur which is at least conceivable; the molecular one that, beginning where the other left off, built up first the diamond and then humanity is one that passes our power to imagine. That out of the aggregation of meteorites should come man, a being able to look back over his own genesis, to be cognizant of it, as it were, from its first beginnings, is almost to prove him immanent in it from the start. Fortunate it is that his powers should seem more limited than his perceptions, and the more so as he goes farther, else he had been but the embodiment of conceit.
We must sketch, therefore, the steps in this marvellous synthesis; hastily, for I have already spoken of it elsewhere in print and repetitions dull appreciation,—in the appreciative,—though we have the best of precedents for believing that, even in science, to be dull and iterative insures success; the dulness passing for wisdom and the iteration tiring opposition out.
In the Sun all substances are in their elemental state. Though its materials are the same as the Earth's, we should certainly not feel at home there, even if we waived the question of comfort, for we should recognize nothing we know. We talk glibly of elements as if we had personal acquaintance with them, man's innate snobbery cropping out. For to the chemist alone are they observable entities. No one but he has ever beheld calcium or silicon, or magnesium, or manganese, and most of us would certainly not know these everyday elements if we met them on the street. Of all the substances composing the Earth's crust, or the air above, or the water beneath, practically the only elements with which we are personally familiar are iron, copper, and carbon, and these only in minute quantities and in that order of acquisition; which accounts for the stone, iron, and bronze ages of man, ending we may add with the graphite or lead-pencil age of early education.
Yet that elementary substances once existed here we have evidence. We find such in volcanic vents. That the Earth was once as hot on its surface as it now is underneath, we know from the condition of the plutonic rocks where sedimentary strata have not covered them up. Volcanoes and geysers are our only avenues now to that earlier state of things. From these pathways to the past, and only from them, do we find elementary substances produced to-day,—hydrogen, sulphur, chlorine, oxygen, and carbon.[1] We are thus made aware that once the Earth was simple, too, on the surface as well as deeper down. A side-light, this, to what we knew must have been the case.
From its primordial state, the least complex compounds were evolved first. As the heat lessened, higher and higher combinations became possible. And this is why the more complex molecules are so unstable, the organic ones the most. Since they are not possible at all under much stir of their atomic constituents, it shows that the bond between them must be feeble—and, therefore, easily broken by other causes besides heat. To the instability of the organic molecule is due 
For the steps in the chemical process from Sun to habitable Earth we must look to the spectroscope; not in its older field, the blue end of the spectrum, but in that which is unfolding to our view in Dr. Slipher's ingenious hands, the extension of the observable part of it into the red. For at that end lie the bands due to planetary absorption. Here we have already secured surprising results as to the atmospheres of the various planets. We have not only found positive evidence of water-vapor in the atmosphere of Mars, but we have detected strange envelopes in the major planets which show a constitution different from that of the Sun on the one hand, and of the Earth on the other. That size and position are for much in these peculiarities, I have already shown you; but something, too, is to be laid at the door of age. The major planets are not so advanced in their planetary history as is our Earth; and Dr. Slipher's spectrograms of them disclose what is now going on in that prefatory, childish stage.
These spectrograms are full of possibilities, and it is not too much to say that chemistry may yet be greatly indebted to the stars. Compounds, the strange unknown substances there revealed by their spectral lines, may be cryptic as yet to us. Some of the elements missing in Mendeléeffs table may be there, too. Helium was first found in the Sun; coronium still awaits detection elsewhere. So with these spectral lines of the outer planets. It looks as if chemistry had been a thought too previous in making free for others with what should have been their names, Zenon and Uranium. For we may yet have to speak of Dion and Varunium.
From the chemical aspect of evolution we pass to its physical side; from the indirectly to the directly visible results. Here again, to learn what happened after the sunlike stage, we must turn to the major planets. For the cooling which induced both physical and chemical change has there progressed less far, inasmuch as a large globe takes longer to cool than a small one. To the largest planets, then, we should look for types of the early planetary stages to-day.
Almost as soon as the telescope was directed to Jupiter, among the details it disclosed were the Jovian belts (in the year 1630), dark streaks ruling the planet's disk parallel to its equator. They are of the first objects advertised as visible in small glasses to-day, vying with the craters in the Moon as purchasable wonders of the sky. As the belts were better and better seen, features came out in them which proved more and more interesting. Cassini, in 1692, noticed that the markings travelled round Jupiter and those nearest his equator the quickest. Sir William Herschel thought them due to Jovian trade-winds, the planet's swift rotation making up for deficiency of sun; why, does not appear.
Modern study of the planet shows that the bright longitudinal layers between the dark belts are unquestionably belts of cloud. Their behavior indicates this, and their intrinsic brightness bears it out. For they are of almost exactly that albedo. Whether they are the kind of cloud with which we are familiar, clouds of water-vapor, we are not yet sure. But whatever their constitution, their conduct is quite other than is exhibited by our own.
In the first place, they are of singular permanence for clouds. The fleeting forms we know as such assume in the Jovian air a stability worthy of Jove himself. In their general outlines, they remain the same for years at a time. "Constant as cloud" would be the proper poetic simile there. But while remaining true to themselves, they prove to be in slow, unequal shift with one another. Thus Jupiter's official day differs according to the watch of the particular belt that times it. Spots in different latitudes drift round lazily in appearance, swiftly in fact, those near the equator as a rule the fastest. Nor is there any hard and fast latitudinal law; it is a go-as-they-please race in which one belt passes its neighbor at a rate sometimes of four hundred miles an hour. The mean day is 9h 55m long.
A side-light is cast upon the Jovian state of things by the "great red spot," which has been more or less visible
Jupiter and its "great red spot"—a drawing by Dr. Lowell, April 12, 7h0 m–5m, 1907
for thirty years, and which takes five minutes longer than the equatorial band to travel round. Its tint bespoke interest in what might be its atmospheric horizon. Yet it betrayed no sign of being either depressed or exalted with regard to the rest of the surface. "In 1891," as Miss Clerke puts it, "an opportunity was offered of determining its altitude relative to a small
dark spot on the same parallel, by which, after months of pursuit, it was finally overtaken. An occultation appeared to be the only alternative from a transit; yet neither occurred. The dark spot chose a third. It coasted round the obstacle in its way, and got damaged beyond recognition in the process." It thus astutely refused to testify.
Now, this exclusiveness on the part of the "great red spot" really offers us an insight to its character. Clearly it was no void, but occupied space with more than ordinary persistency. As it was neither above nor below the dark spot and shattered that spot on
approach, which its former surroundings had not done, its force must have been due to motion. This can be explained by its being formed of a vast uprush of heated vapor from the interior. In short, it was a sort of baby elephant of a volcano, or geyser, occurring as befits its youth in fluid, not solid, conditions, but fairly permanent, nevertheless—a bit of kindergarten Jovian geology. This estimate of it is concurred in by Dr. Slipher's spectrogram of the dark and light belts respectively. For in the spectrum of the dark one we see
Photograph of a Sun spot—after the late M. Janssen
the distinctive Jovian bands intensified as if the light had traversed a greater depth of Jovian air. Its color, a cherry red, abets the conclusion—that in such places we look down into the fiery, chaotic turmoil so incessantly going on.
It is of interest to note that we have prototypes of this sort of extraterrestrial cyclone in the Sun. His spots are probably local upsettings of atmospheric equilibrium, using the word atmospheric in the widest possible sense. Just as our storms are the mildest examples of the like expostulation at the impossibility of keeping up a too long continued decorum. Only that with us the Earth is not so much to blame as the Sun; while both Jupiter and the Sun are themselves responsible for their condition.
Thus we have, in the very depth of their negation, warrant from the dark belts of Jupiter that the bright ones are cloud. But also that they are not clouds ordered as ours. The Jovian clouds pay no sort of regard to the Sun. In orbital matters Jupiter obeys the ruler of the system; but he suffers no interference from him in his domestic affairs. His cloud-belts behave as if the Sun did not exist. Day and night cause no difference in them; nor does the Jovian year. They come when they will; last for months, years, decades; and disappear in like manner. They are sui Jovis, caused by vertical currents from the heated core and strung out in longitudinal procession by Jupiter's spin. They are self-raised, not sun-raised, condensations of what is vaporized below. Jove is indeed the cloud-compeller his name implies.
Yet Jupiter emits no light, unless the cherry red of his darker belts be considered its last lingering glow. He is thus on the road from Sun to world, and his present appearance informs us that this incubation takes place under cloud.
The like is true of Saturn, in fainter replica, even to the cherry hue. In one way Saturn visibly asserts his independence beyond that possible by Jupiter. For Jupiter's equator lies almost in the plane of his orbit, and on a hasty view the Sun might be credited with the ordering of the belts, as was indeed long the case. But Saturn's inclination to his orbital plane is 27°; yet his belts fit his figure as neatly as his rings, and never get displaced, no matter how his body be turned.
Uranus and Neptune are in the same self-centred attitude at present as the faint traces of belts on their disk, otherwise of the same albedo as cloud, lead us to conclude. Yet both their densities and their situation give us to believe them further advanced than the giant planets, and still they lie wrapped in cloud.
These planets, then, are quite unbeholden to the Sun for all their present internal economies. What goes on under that veil of clouds with which they discreetly hide their doings from the too curious astronomic eye—we can only conjecture. But we discern enough to know that it is no placid uneventfulness. That it will continue, too, we are assured. For whether these clouds are largely water-vapor now, or not, to watery ones they must come as the last of all the wrappers they will eventually put off.
The major planets are the only ones at the present moment in this self-centred and self-sustained stage. Their great size has kept them young. In the smaller terrestrial planets we could not expect to witness any such condition to-day. If they experienced an ebullient youth, they have long since outgrown it. Only by rummaging their past could we find evidence on the point, and this, distance both in time and space bars
us from doing. There is but one body into whose foretime career we could hope to peer with the slightest prospect of success—our own Earth.
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 one time 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
Ideal section of a laccolith—Gilbert.
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. A very 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 evolutionary 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[2] 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,[3] 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 
To understand the problem from the Earth's point of view, let us review the facts with which geology presents us. The flora of paleologic times, as we see both at their advent in the Devonian and from their superb development in the Carboniferous era, consisted wholly of forms whose descendants now seek the shade.[4] Tree ferns, sigillaria, equisetæ, and other gloom-seeking plants composed it. That some tree-fern survivals today can bear the light does not invalidate the racial tendency. We have plenty of instances in nature of such adaptability to changed conditions. In fact, the dying out and deterioration of most of the order shows that the conditions have changed. And these plants, grown to the dimensions of trees, inhabited equally the tropic, the temperate, and the frigid zones as we know them now. Lastly, no annual rings of growth are to be found on them.[5]In other words, they grew right on, day in, day out. The climate, then, was as continuous as it was widespread.
On the other hand, astronomy and geology both assert that the seas were warm.[6] From this it follows that a vastly greater evaporation must have gone on then than now, and that a welkin of cloud must thus inevitably have been formed.
Now put the two facts together, and you have the solution. The climate was warm and equable over the whole globe because a thick cloud envelope shut off the Sun's heat, the heat being wholly supplied from the steamy seas. At the same time, by the same means the light was necessarily so tempered as to produce exactly that half-light the ferns so dearly love. One and the same cause thus answers the double riddle of greater warmth and less light in those old days than is now the case.
And here comes in the second find I spoke of above, in the person of some old trilobites who stepped in unexpectedly in corroboration. It has long been known—though its full significance seems to have escaped notice—that in 1872 M. Barrande made the discovery that many species of trilobites of the Cambrian and lower Silurian, the two lowest, and therefore the oldest, strata of paleozoic times, and distant relative of our horseshoe crabs, were blind. What is yet more significant, the most antediluvian were the least provided with eyes. Thus in the primordial strata, one-fourth of the whole number of species were eyeless, in the next above one-fifth, and in the latest of all one two-hundredth only.[7] Furthermore, they testify to the difficulty of seeing, in two distinct ways, some by having no eyes and some colossal ones, strenuous individuals increasing their equipment and the lazy letting it lapse. It seems more than questionable to attribute this blindness to a deep-sea habitat, as Suess does in describing them, for they lived in what geologists agree were shallow seas on the site of Bohemia to-day. Besides, trilobites never had abyssal proclivities; for they are found preserved in littoral deposits, not in deep-sea silt. Muddy water may have had some hand in this, but muddy water itself testifies to great commotion above and torrential rains. So the light in those seas was not what it became later, or would be now. Thus these trilobites were antelucan members of their brotherhood, and this accuses a lack of light in those earlier eras even greater than in Carboniferous times, which is just where it ought to be found if the theory is true.
I trust this conception may prove acceptable to geologists, for it seems imperative from the astronomic side that something of the sort must have occurred. And it is just as well, if not better, to view it thus in the light of the dawn of geologic history as to remain in the dark about it altogether. Nescience is not science—whether hyphenized or apart; for the whole object of science is to synthesize and explain. Its body of learning is but the letter, coordination the spirit, of its law. Nevertheless, the unpardonable impropriety of a new idea, I am aware, is as reprehensible as the atrocious crime of being a young man. Yet the world could not get on without both. Time is a sure reformer and will render the most hardened case of youth senile in the end. So even a new idea may grow respectable at last. And it is really as well to make its acquaintance while it still has vigor in it as to wait till it is old and may be embraced with impunity. Boasted conservatism is troglodytic, and usually proves a self-conferred euphuism for dull. For conservatism proceeds from slowness of apprehension. It may be necessary for certain minds to be in the rear of the procession, but it is of doubtful glory to find distinction in the fact.
Thus the youth of a world, like the babyhood of an individual, is passed screened from immediate contact from without. That this is the only way that life can originate on a planet we cannot say, but that it is away in which it does occur, our own Earth attests, and that, moreover, it is the way with all planets of sufficient size, the present aspect of the major planets shows. It may well be that with celestial bodies as with earthly species, some swaddle their young, others cast them forth to take their chance, and that those that most protect them rear the higher progeny in the end. What glories in evolution thus await the giant planets when they shall have sufficiently cooled down, we can only dimly imagine. But we can foresee enough to realize that we are not the sum of our solar system's possibilities, and by studying the skies read there a future more wonderful than anything we know.