The Romance of Modern Geology / Describing in simple but exact language the making of the earth with some account of prehistoric animal life

by Edwin Sharpe Grew

CHAPTER VIII

THE EARTH AT ITS BEGINNING

If we look up at the sky with the eye of knowledge we can read in the celestial objects with which it is strewn something of the history of our earth. We can only read it dimly even with the aid of the greatest telescopes, and it is quite possible that in some respects we may read it wrongly. Let us, however, consider what the eye and the telescope will reveal to us. The eye will see the Sun—a great ball, into which the earth might sink without greatly altering the Sun's appearance, and surrounded with flaming gases hotter than the hottest furnace man has ever been able to contrive. In that heat every solid thing on the earth would melt and be turned into vapour. The eye will also perceive the Moon—another ball, much smaller than the earth, surrounded by no gases at all, having as far as can be seen no water; and being so cold during its long nights that all gases and liquids of which we know would be frozen solid there.

The eye can also see a myriad of stars of varying brightness, but for the most part only thus distinguishable. If the telescope be now called in to aid, the eye will, however, be able to discern differences and distinctions in the stars. It will see that some are balls like the Earth, the Sun, and the Moon. If these balls are studied attentively we shall discover that one of them, Jupiter, is a great deal hotter than the earth, though a great deal cooler than the Sun; and that another of them, Mars, is a great deal colder than the earth, but a great deal warmer than the Moon. Perhaps we might now begin to surmise that the Sun coming first, Jupiter next, the Earth next, Mars next, and the Moon last, were all like stages in the history of one of these balls; and that, for example, any one ball began by being as hot as the Sun, and ended, after passing through stages like Jupiter, the Earth, and Mars, in being as cold and lifeless as the Moon.

But if one had a very good telescope, and could examine those more distant specks of light which we call stars, we perhaps could spy a little earlier into the history of these great balls. For example, among the blazing lights of the heavens—the stars which we know to be suns—there are others which are not balls at all. There are the Pleiades, for instance, of whom the Prophet Amos wrote, "Seek Him that maketh the seven stars and Orion" (Amos v. 8). The seven stars (in the Authorised Version rendered Pleiades),[4] when seen through a great telescope, are caught in a mesh or a veil of something that may be starry matter, but of the exact nature of which we are uncertain. In other parts of the sky there are great masses of this starry mist; and to these bright patches astronomers have given the name of "nebulæ." The most wonderful of them all is the great nebula in Orion;[5] and one of the most beautiful is the great spiral nebula of Andromeda. These objects are not only wonderful and beautiful; they also give us a hint as to what might have been the earliest state of our earth, and of the Sun itself in those almost inconceivably distant ages before order took the place of chaos.

[4] It has been cogently suggested that by the "seven stars" the biblical writer meant the constellation of the Great Bear; but Mr. E. W. Maunder, F.R.A.S., of Greenwich Observatory, is of opinion that the Pleiades were signified.

[5] "God maketh Arcturus, Orion, and Pleiades, and the chambers of the south" (Job IX. 9).

Let us ask the reader to imagine what would take place if the earth were to come into collision with another planet. Some of our readers, at any rate, will know that the Sun and all its planets—the earth among them—is moving swiftly to some unknown destination among the stars.[6] Suppose that some great planet, not of the Solar System, barred our path. We should not be taken wholly unawares, for astronomers would know of the approach of the star and our earth to one another months, and perhaps years, beforehand. That would be because the light of the Sun falling on it would be reflected, just as the reflection of the Sun's rays light up the Moon for our eyes. If the strange planet were a very large body, like the sun for bigness, it would become visible far beyond the confines of the Solar System. It might first be taken for a new star such as sometimes blazes up in the sky and then sinks into darkness again. But its steadiness would make it an object of suspicion. There would be another brief period in which it might be taken for a comet; but comets have a light quite different from that of reflected sunlight. So that anxious expectation would be dissipated, and the world would begin to recognise the monster for what it really was. If its size were the same as that of the Sun, then it would first become visible to us when 15,000,000,000 miles distant,[7] or let us say 1600 times farther away from us than we are from the Sun. We and it would approach slowly at first. It would be nearly ten years before the distance had been reduced to 6,000,000,000 of miles, and the intruder had begun to be visible to the naked eye. In fourteen years it would have reached the outer edge of the Solar System, and would be the brightest star in the heavens. In another year it would be twice as bright as Venus at her brightest, and would be coming nearer with appalling swiftness. In less than two months it would be as near the Sun as we are. In a week more it would have plunged into the Sun at the rate of 400 miles a second, and in the awful heat born in that collision, Sun and earth and planets would be molten, and the Solar System overwhelmed

In unremorseful folds of rolling fire.

[6] It is usually supposed that this movement, amounting to perhaps ten miles a second, is in the direction of the constellation of Vega.

[7] See an article by Mr. Ellard Gore in Knowledge, November, 1905. The object would not be visible at this distance except through large telescopes.

Suppose that this catastrophe were to take place. Would that be the end of all things? No. Out of the fiery mist many millions of miles across—like one of those great nebulæ which the telescopes reveal to us—order would be evolved. Two things would at once begin to happen, since in the Universe nothing stands still. The fiery mist would be giving out heat all about it, sending out heat-waves as a fire or a red-hot poker will do. The red-hot poker cools; so, too, would the fiery nebula. Then the nebula would begin to condense; not quite in the same way that a cloud of steam does, for it would be whirling all the time, and its fiery particles would be all trying to fall inwards, just as anything dropped from our hands tends to fall towards the centre of the earth. As this whirling mass of gas condensed some great masses of it would become detached, and would begin to enjoy separate existences of their own.

Let us imagine, for the sake of argument, that a mass of gas vast enough, when it condensed, to form the earth itself became detached from the parent nebula. Suppose we follow its history. At first it may have been a globe hardly distinguishable from a whirling flame. In brightness it was like the Sun, and like the Sun, it was covered with elemental gases. It was, in fact, in its earliest days a sphere of gas continually giving out heat, and continually cooling, till from a sphere like the Sun it became a ball like Jupiter. It had an intermediate stage when its gases were condensing into liquids, as steam condenses into water; for though the nebula as a whole was hot it was always travelling through cold space. Gradually the earth became partly liquid and partly gas. For millions of years it continued to revolve as a ball of liquid—still cooling—still being pressed very hard at its central parts by the weight of all the gases and liquids round it, till at last the first crust of solid matter began to form on the liquid surface. This crust continued to thicken, but it was subject to many appalling catastrophes and breakages.

We have already used the occurrence of the tides of the earth as an instance of the Sun's attraction. The Sun (and the Moon) attract the waters of the earth, pulling them up towards themselves. So would they also attract the molten materials of which the early earth was composed. The liquid mass would be continually surging like a tide against its wall of solid crust, and the liquid would now and again burst through. There must have been a time when the thin solid crust covering the molten interior became, owing to the solidification and contraction of the crust, much too small to contain the liquid material. The lava would then break through, and would form huge craters, not unlike some of those which we see on the Moon. We can faintly imagine these terrible outbreaks in which the molten tide rose not thirty or forty feet but many miles high!

Later, after some relief had been given by these outbreaks and the crust thickened, the interior regions of the earth by cooling shrank away from the solid shell, which was now too large. This solid shell being insufficiently supported sometimes caved in, and other great outflows of lava resulted. These lava floods dissolved the original solid shell whenever they came in contact with it. The earth probably once had gigantic craters like those which we can see in their extinct form on the Moon; but they were destroyed by these outflows of lava of which we have spoken.

Then, still cooling, the earth's crust grew thicker and thicker. The great outflows and eruptions of molten elements from underneath grew fewer, and more liquid elements cooled into solids, and more gases condensed into liquids. There was another thing happening of which, as conscientious recorders of the history of the earth's geology, we must take note; and it is that in those early days meteorites were falling on the earth in vastly greater numbers than they do to-day. Meteorites are masses of cooled rock flying through space which still occasionally fall on the earth, and specimens of them are still to be found, many of them preserved in museums, such as the Natural History Museum in Cromwell Road, London. But the earth in its path has swept most of them up, as the housemaid's dusting-pan collects the fragments of dust. When the earth was young there were incomparably more fragments to collect, and they fell on the earth like rain.

Meanwhile the cooling water vapour became the oceans; clouds and rain and cool winds and eventually snow and ice became possible; and the hardening lavas, or fire-born rocks, became subject to their influences, till above them were raised the stratified rocks, of which we have spoken in our earlier chapters, and the lineage and descent of which is part of the study of geology. On the earth most of the traces of its earlier history have been removed, but there are some signs of them perceptible to the comprehending eye. The earth is probably seamed with great cracks that do not now reach to the surface, but which are indicated by the presence of chains of volcanoes. The volcanoes of the great chains of the Andes lie along a straight crack reaching from Southern Peru to Terra del Fuego, 2500 miles in length. The volcanoes of the Aleutian Islands lie along a curved track equally long. Other shorter lines of volcanoes are very numerous, and since countless others existed in former times, the cracks in the earth's crust must be exceedingly numerous. There is one crack which comes to the surface in various places in Eastern Asia and Western Africa, and stretching from the Dead Sea to Lake Nyassa, reaches the enormous length of 3500 miles.

From this brief sketch of the formation of the earth, its progress and processes, and from the hints which the volcanoes and earthquakes of to-day afford us, we may obtain some idea of the underworld that lies far beneath our feet. Not much, however, for we are ignorant of the actual conditions which exist towards the centre of the earth. But there seems a strong case for supposing that there is an outer solid crust of earth and an inner molten core of very great heat.