Where did the moon come from? Is it space debris or a chunk of the earth? This article from 1905 presents the argument that the moon was once a piece of the earth.
The Earth’s Daughter
Hawaii’s Volcanoes Show That Moon Once Occupied Present Bed of Pacific Ocean
By William H. Pickering
Professor of Astronomy, Harvard University
THAT the moon, our sister planet, was originally torn away from the earth, we are forced to believe. The period of its birth we locate somewhere between fifty million and five hundred million years ago. But there are many facts connected with this great change which still lie in the realm of speculation and theory, and some of them were brought home to me last summer, while I was studying the Hawaiian volcanoes, with an emphasis which seems worthy of a special note.
In the Hawaiian Islands rise perhaps the finest group of volcanic peaks upon our globe. Enormous in their height and tremendous in their activity, they differ from other volcanoes in many respects which lend them special importance in the study of the moon’s origin. In the Island of Hawaii I found, lying black and sterile amid the magnificent growth of palms, bananas and tropical foliage, the great black lava-bed which swept down from Mauna Loa in 1880. It burst forth from the side of the mountain at a height of eleven thousand feet above the sea and a distance of seven miles from the nearest wall of the summit crater. It continued to flow for nine months, making straight for the town of Hilo, thirty-one miles away.
As an interesting commentary upon original belief and educated faith, the action of the natives may be noted. In great terror as the molten flow steadily approached their homes, they met constantly in their churches and prayed fervently that the flow might be arrested. Christianity had gained a firm hold among them fifty years before, and they trusted to it in their prayers; but finally the great burning flood continuing to advance unchecked, they lost heart and reverted to Paganism. They flocked en masse to Princess Ruth, one of the few survivors of the old line of native chiefs, and implored her to offer a sacrifice to Pele, the dread goddess of the volcano.
Ruth promptly came to the rescue, and without omitting a single one of the ancient sacred and traditional forms she solemnly sacrificed a pig, a white rooster and a bottle of wine, vintage not stated, by throwing into the on-moving lava whereupon the on-moving lava stopped instantly a mile outside the town. That it stopped on the date given is certain, and the Christian propaganda at Hilo since that day has been attended with some difficulty. Skeptical science, however, has hitherto declined to recognize any definite relation between volcanic action and a pig, a white rooster or even a bottle of wine.
The crater of Kilauea is the largest active crater in the world. It measures three miles by two, and near the center is located a pit known as Halemaumau, twelve hundred feet in diameter, with nearly vertical walls, and five hundred feet deep. This pit is gradually filling up with melted lava from below, and whenever this lava reaches the rim and begins to overflow the phenomena exhibited are said to be grand beyond description. It was last full to the brim in 1892; but on this occasion, contrary to rule, it emptied itself through some subterranean channel in a single night. Since then the crater has shown little activity, though red hot lava flows from thirty to fifty feet in length are sometimes seen at night at the bottom of the pit.
However before proceeding to consider the new evidence offered by Kilauea and its attendant volcanoes — evidence new to me at least — let us briefly review our existing knowledge concerning the moon’s origin. In order to understand it, we must first consider the mutual influences that the earth and moon exert upon each other at the present time. We all know that the moon creates a double tide upon the earth. If there were no continents to interfere, and if the ocean was deep enough, one of these tides would be always on the side of the earth toward the moon, and the other tide on the opposite side. There are two tides, because in one case the water nearest the moon is pulled away from the center of the earth is pulled away from the water that is still farther from the moon. This pulling force of the moon acts on the continents that are on opposite sides of the earth as well as on the oceans, but the continents being solid cannot yield and so move all in one piece, and only the oceans show the effect of the pull.
Bodies Of Water
As the result of the tides and the earth’s rotation, large bodies of water are being constantly moved about over the earth’s surface. We may indeed consider the earth as a wheel steadily revolving between two friction brakes, much as a grindstone might do. The result of this action is that the speed of the earth’s rotation is constantly diminishing, every day being a little longer than its predecessor. That this may not occasion alarm among those who work by the hour, I hasten to add that the total lengthening of the day that has taken place since the beginning of the Christian era amounts to only a small fraction of a second. But this was not always so. In the early days, before the oceans appeared, and when a large part of the solid earth was molten matter, tremendous tides occurred in this mass of liquid rock, tides which were much more efficient in this respect than those now in existence.
But if the earth’s rotation is being constantly held back by this action of the moon, since action and reaction are equal and opposite, the moon must constantly be pulled forward in its orbit by the earth. If the moon’s velocity is accelerated, its centrifugal force will be increased, and as a result it will tend every day to fly farther and farther away from the earth. If next year the moon will be farther from the earth than it is today, then this year it must have been farther than it was the year before, and since the action is obviously continuous, in early times it is certain not only that the earth revolved faster on its axis, but also that the moon revolved nearer to the earth’s surface.
In those early days, since the moon was nearer, the tides must have been higher, and therefore more effective, so that these actions must have been still more pronounces than they are at present. Carrying the process back therefore to its beginning, we come to a time when the moon must have laid close to the earth’s surface, and when the earth must have revolved exceedingly fast.
It has been shown by Professor George H. Darwin, son of the eminent naturalist, that at the time when the moon nearly touched earth’s surface the earth must have revolved on its axis once in about three hours, instead of once in twenty four. Now it can readily be shown that if the earth was to revolve on its axis in a little less than three hours portions of its surface near the equator would be likely to fly away by centrifugal force.
As the original cloudlets from which the earth was formed coalesced and revolved about the sun, they rotated upon their common axis, and as they condensed they must necessarily have rotated more and more rapidly. This rotation was doubtless somewhat diminished by the action of the tides produced in them by the sun, but as we have seen at a much later time, when the moon was near the earth they were revolving in about three hours. The presence of the moon must have already produced a retarding action, so that a little earlier, before the moon appeared, they must have been revolving still faster.
But this high speed could have been attained in only a comparatively small body, a body, that is to say, a little larger than the earth is at present. As its speed of rotation increased, its centrifugal force must have increased also, consequently objects near its equator must have risen higher and higher. Thus action went on, gradually becoming more and more critical, until one day a catastrophe occurred, a catastrophe of such magnitude as has never been seen upon the earth before or since — five thousand million cubic miles of material left the earth’s surface never again to return to it. Whether it all left at once or the action was prolonged we do not know, but we may try in vain to imagine the awful uproar and fearful volcanic phenomena exhibited when a planet was cleft in twain and a new planet was born into the solar system. This was the moon’s origin.
As to how long ago this separation occurred we are entirely in the dark, but we know that as astronomical events go it must have been rather recent, since the earth had already assumed about its present dimensions. Indeed, the moon must be one of the younger members of the solar system. At the same time its age, as I have said, cannot be less then fifty million years, and is more likely five hundred million.
That the material composing the moon was torn away from the surface of the earth we are well assured by what we certainly know concerning the moon’s density. The density of the whole earth is five and one half times greater than that of water. The density of the surface of the earth as we now know it is about two and one-half; so that the density of the central regions must be much higher, and they are probably largely metallic. The average density of the moon is only three and one-half, so it is clear that the materials forming it were gathered from the earth’s surface, and just below it rather than from toward the center of the earth.
The place where the moon was torn away has ever been an interesting problem, and it was upon this division of the question that new light was shed by the volcanoes of Hawaii.
As I saw them for the first time, explored them and studied them, they seemed more like a part of the moon than a part of the earth. Long familiar with the moon’s surface as revealed by a powerful telescope, I have found portions of it exactly reproduced in the general plan and smaller details of the lava formations. Photographs of many parts of it, taken from a balloon, would have been declared by many astronomers, at first sight, to be lunar photographs. Outside of the pit of Kilauea on the floor of the great crater were lava forms twelve to twenty feet in height shaped exactly like the central peak or ridge as we see them in the moon’s volcanoes. Here too were the lunar rills, great cracks six to eight feet in breadth, a mile in length and of such great depth, that they are popularly regarded as bottomless.
The suggestion has been made that the mass of the moon, when torn away from the earth, left the great scar now filled by the Pacific Ocean, and the shape of the ocean, supplemented by the peculiarities of the Hawaiian volcanoes, certainly goes far to support that view.
The coastline of the Pacific is nearly that of a great circle whose center lies on the Tropic of Capricorn, in longitude one hundred and seventy west, about five hundred miles south of Samoa. It is bounded everywhere, from Cape Horn to the East Indies, by a continuous row of active or extinct volcanoes. Toward the center of this circle the volcanic peaks of Hawaii, Samoa and New Zealand are situated with reference to the circumference much as the central peaks of a lunar volcano are situated with reference to the rim. In other words, the general shape of the bed of the Pacific Ocean is that of the crater of a great volcano, much like Kilauea, much like the great craters of the moon.
Now, the bed of the Atlantic Ocean has an entirely different shape, and this difference has never been explained. Generally speaking, its eastern coastline and its western coastline fit into each other so naturally and so symmetrically that they seem to be parts of a torn fabric. This is so greatly true that it is not unreasonable to suppose that they were torn apart; that when some great cataclysm occurred where the bed of the Pacific now is the newly formed crust of the earth was so torn apart and shifted that the rent formed the bed of the Atlantic as the departing mass formed the circular bed of the Pacific. When the earth had sufficiently cooled for water to condense these two depressions appear to have filled and to have thus formed our two great oceans. If the reader will take an ordinary terrestrial globe and draw a line from the southern point of Nova Scotia to the coast of Dutch Guiana, and then suppose all the region west of this line to be land, as appears to have once been the case, the way in which the two sides of the Atlantic fit together will strikingly appear.
In further support of the theory is the strong probability that the earth’s surface was solid when the moon was created, and the certainty, this being so, that the catastrophe would have left a permanent scar. Geologists are not unanimous regarding these questions, but the majority hold that the ocean beds are permanent features of the earth’s surface, protected as they are from atmospheric erosion, and have suffered no change in geological time.
From the standpoint of quantity it would have required a shell of matter covering all the ocean surface to a depth of thirty five miles to form a spherical body the size of the moon. This depth we may therefore take on this supposition as the thickness of the crust of the earth at that time. Since the average depth of the ocean is about three miles, this crust was floating on the earth’s liquid interior, immersed to a depth of thirty two miles. The density of this crust as we find it in the moon (three and one-half) gives us a not improbable value, bearing out the supposition.
When first thrown off, the moon cannot have had its present shape, as the attractive force of the earth would not have permitted a spherical body of such size to exist in its immediate vicinity. It possibly took the form of a ring, more or less irregular, surrounding the earth’s equator, and was probably composed of a large number of separate bodies which, as they receded, coalesced and eventually took the present spherical shape.
Having now looked back into the past as far as modern science can see, let us turn in the opposite direction and learn what the future has in store for us. Are we going to lose our moon after all?Apparently not, for the recession is limited. The moon may continue to recede until it reaches a distance of three hundred and fifty thousand miles, or about half as far again as it is now. Its month will then last fifty of our present days. Our day at that remote epoch will also have increased and be fifty times as long as it is at present. The earth and moon will then constantly present the same face to one another. The moon will cease to rise and set, there will be one point on the earth’s surface where the moon will be always overhead, and people living on the other side of the earth will never see the moon at all. After that the tides will peace to act, a permanent condition will have been reached, and no further change will be possible.
That this condition of affairs cannot occur in many millions of years is obvious, but is it not possible that in the meantime other events may occur which will modify or entirely change the order of procedure? To this question science gives a pretty distinct affirmative. The moon will cease to recede as soon as the tides cease to exist, and the tides will cease to exist as soon as the ocean dries up, or freezes into one solid mass. Whether in the future the ocean will dry up, we cannot say, although it looks as if it would, unless it first freezes solid.
The heat of our sun is maintained by a steady contraction of its bulk, amounting to an annual diminution of about two hundred and fifty feet in its diameter. The sun’s diameter is about a million miles, and although this diminution is small, it is clear that it cannot go on forever. In short, before long, astronomically speaking, the heat of the sun must begin to diminish sensibly. Professor Newcomb concludes that in five million years it will be giving out less than half its present supply of heat. Long before that time our oceans will have frozen over, and soon after that occurs our Eskimo posterity will have disappeared off the face of this frozen planet, so it is not likely that any of our descendants will ever live to see a stationary distant moon and a many times lengthened day.
In closing, it may be well to call attention to the fact that while we have at present no means either to prove or disprove this suggestion as to the birthplace of the moon, it is a point in its favor that it explains three facts for which no explanation whatever has before been offered: first the resemblance of the Atlantic coastline of the eastern and western continents; second, the contrast between the character of the Atlantic and Pacific continental coasts; and third, the existence of the permanent ocean beds.
Source: Evening Star. Newspaper. November 12, 1905.
