Harper's Round Table, August 20, 1895

by Various

A RING THROWN FROM THE SUN FORMING A SEPARATE PLANET.

The studies of astronomers have made it evident that in the olden days, indeed before days began, at a time which is to be reckoned as many hundred million years ago, the sun and the other bodies of the solar system, including our earth, the kindred planets and their satellites, were parts of a great mass of vapor or star dust, which extended throughout the spaces in which these spheres now swing about the sun. As time went on this nebulous mass, just like many such masses which the telescope reveals in the distant heavens, drew together, because its particles were impelled by gravitation towards the central point, and as it contracted it began to revolve, much as our earth and the other spheres as well now turn on their axes. Thus turning, it divided into successively formed rings, each of which in time broke up, the matter of the ring gathering into a separate planet. At first this planet, like the original mass, was gaslike, and when separated from the sun it began to gather in on itself, in most cases forming rings, which in time were to alter into the lesser spheres—the moons. The earth and all the planets lying further away from the sun have these little bodies about them, but in one case, as if to show the stages of creation, the unbroken ring remains, forming the magnificent circles which girdle Saturn. When, in the history of these wonderful processes of growth which have taken place in our solar system, our earth parted from the shrinking sun, the separate life of the sphere began. In the course of ages it set off the mass of the moon, and after that process was effected by further shrinking, it was reduced from a body several hundred thousand miles in diameter to a relatively small sphere. Such are the steps which led to the birth of our planet.

As the earth's matter gathered into a smaller bulk, its heat was greatly increased, so that for a time it was a hot, shining star like the sun. Gradually, however, it parted with so much of its heat that it, as we may say, froze over or became covered with a solid crust which soon became cool enough to permit the waters hitherto in the state of steam to descend upon the surface of the sphere. With this descent of the waters, which led to the formation of the seas, another stage of great importance in the history of the earth began. In the earlier ages the heat of the earth, which came from within its mass, was so great that the temperature coming from the sun was of no consequence, but when the earth acquired a crust of cold rocks, a new period began, that in which the solar heat was thereafter to be the source of most of the movements that occurred in this limited world. Thenceforward to the present day, and yet on through the ages, the sun and earth are linked together in their actions in a marvellously entangled way.

When the sun's heat began effectively to work on the earth in the manner which we now behold, the winds began to blow, the ocean waters under their influence to circulate currents, and the moisture to rise into the air to be carried to and fro and to fall as rain. It seems likely that these movements of air and water, which we know to be due to the action of the sun's heat, took place at first upon the surface which was everywhere covered by the ocean, a vast continuous sea through which the lands had not yet pierced, and in which living creatures had not begun to dwell. This universal field of waters could not have long continued, and this for the reason that certain changes in the earth itself brought about the creation of broad folds on the sea-bottom, which grew upward until dry lands rose above the level of the waters. The way in which this process took place can in general be easily understood.

After the earth had cooled to the point where its outer parts were what we term cold, and the whole of its mass approximately solid, it remained as it does to-day, exceedingly hot in its central portions, and therefore kept on slowly cooling. What we call the outer or crust part, because it had already become cool, had little heat to lose. The greater portion of the temperature, which crept away into the frigid places of the heavens, where the thermometer is always some hundred degrees below the freezing-point, came from the interior of the sphere. Because of this cooling in the deeper parts of the earth the mass shrunk in its interior portion, while the outer part, losing less heat, because it had less to lose, did not contract to anything like the same extent. Thus it came about that this crust portion which forms the surface, and that which is below to the depth of many miles, were forced to wrinkle in order to fit the diminished centre. The action may be compared, in a way, to what takes place when in an apple or other similar fruit or vegetable with a distinct skin the water dries out of the interior parts. The skin wrinkles, because it has little water to lose. Let us conceive that the heat which keeps the particles of matter apart in our earth answers to the water which separates the solid portions of the fruit, and the likeness becomes clear.

When the great wrinkles of the earth's crust were high enough to bring their surfaces in part above the level of the ocean, another important stage in the history of the sphere was begun. Before that time, the water which the sun's heat had lifted into the air, and sent back to the earth in the form of rain, had fallen into the ocean whence it came without in any way affecting the solid parts of the crust. But now a portion of it came down on what we call the dry land, making the beginning of the rivers and the lakes, and in its course to the sea wearing away the rocks over which it flowed, conveying the débris to the oceans, where it served to build layers of rocks upon the bottom, which with the further upward growth of the continent might in turn rise above the sea. Thus we may fairly reckon the appearance of the land above the seas as the third great event in the history of the earth.

After the earth had cooled down so that the waters had something like their present temperature, and probably after the lands had appeared, came the fourth and, on many accounts, the most interesting episode in the history of the planet. This was the beginning of what we call life, those little temporary gatherings of the earth's substance which take shape in the form of animals and plants. As yet we do not know, we are not likely indeed ever to know, just when or how this change from the earlier stage in which the earth knew no living creatures to that in which they were to abound in seas and on land. All that has been found out concerning the matter leads us to believe that the first steps led to the creation of very simple species—jellylike forms having but few of the qualities which we commonly associate with living beings. But the first steps taken in the immemorable ages, the others followed in quick succession, so that the earliest fossil remains which we find in rocks formed on the sea-bottom, a hundred million or more years ago, show that the earth was richly peopled with a lowly life.

Probably at some time after the lands had risen above the sea, and had begun to yield their waste in the form of mud, sand, and pebbles, to provide strata on the sea-bottoms, volcanoes began to break forth on the sea-bottom and along the margins of the continents. These strange outbursts, mainly of steam, but often accompanied by molten rock, appear to owe their formation to the accumulation of beds on the bottom of the ocean, which as they are formed are to a great extent filled with water. Accumulated to a thickness of many miles, the water in the lower part of these strata gradually becomes exceedingly heated. In the end it breaks forth in steam, having a temperature quite as hot as molten iron, so that it may melt ordinary rocks.

The beginning of volcanic action on the earth was in a way important, though the event is less noteworthy than any of those which have been previously remarked, for tremendous as a volcanic eruption may be (that of Kratakoa in 1883 shook a large part of the earth's surface, perturbed all its atmosphere, and sent its dust to every part of the world), they, after all, are not leading features in the earth's history, but rather incidents. It is otherwise with the last great physical event in the history of the earth, which we shall now have to consider.