The Outline of History/Chapter 1
THE OUTLINE OF HISTORY
I
THE EARTH IN SPACE AND TIME
THE earth on which we live is a spinning globe. Vast though it seems to us, it is a mere speck of matter in the greater vastness of space.
Space is, for the most part, emptiness. At great intervals there are in this emptiness flaring centres of heat and light, the "fixed stars." They are all moving about in space, notwithstanding that they are called fixed stars, but for a long time men did not realize their motion. They are so vast and at such tremendous distances that their motion is not perceived. Only in the course of many thousands of years is it appreciable. These fixed stars are so far off that, for all their immensity, they seem to be, even when we look at them through the most powerful telescopes, mere points of light, brighter or less bright. A few, however, when we turn a telescope upon them, are seen to be whirls and clouds of shining vapour which we call nebulæ. They are so far off that a movement of millions of miles would be imperceptible.
One star, however, is so near to us that it is like a great ball of flame. This one is the sun. The sun is itself in its nature like a fixed star, but it differs from the other fixed stars in appearance because it is beyond comparison nearer than they are; and because it is nearer men have been able to learn something of its nature. Its mean distance from the earth is ninety-three million miles. It is a mass of flaming matter, having a diameter of 866,000 miles. Its bulk is a million and a quarter times the bulk of our earth.
These are difficult figures for the imagination. If a bullet fired from a Maxim gun at the sun kept its muzzle velocity unimpaired, it would take seven years to reach the sun. And yet we say the sun is near, measured by the scale of the stars. If the earth were a small ball, one inch in diameter, the sun would be a globe of nine feet diameter; it would fill a small bedroom. It is spinning round on its axis, but since it is an incandescent fluid, its polar regions do not travel with the same velocity as its equator, the surface of which rotates in about twenty-five days. The surface visible to us consists of clouds of incandescent metallic vapour. At what lies below we can only guess. So hot is the sun's atmosphere that iron, nickel, copper, and tin are present in it in a gaseous state. About it at great distances circle not only our earth, but certain kindred bodies called the planets. These shine in the sky because they reflect the light of the sun; they are near enough for us to note their movements quite easily. Night by night their positions change with regard to the fixed stars.
It is well to understand how empty space is. If, as we have said, the sun were a ball nine feet across, our earth would, in proportion, be the size of a one-inch ball, and at a distance of 323 yards from the sun. The moon would be a speck the size of a small pea, thirty inches from the earth. Nearer to the sun than the earth would be two other very similar specks, the planets Mercury and Venus, at a distance of 125 and 250 yards respectively. Beyond the earth would come the planets Mars, Jupiter, Saturn, Uranus, and Neptune, at distances of 500, 1806, 3000, 6000, and 9500 yards respectively. There would also be a certain number of very much smaller specks, flying about amongst these planets, more particularly a number called the asteroids circling between Mars and Jupiter, and occasionally a little puff of more or less luminous vapour and dust would drift into the system from the almost limitless emptiness beyond. Such a puff is what we call a comet. All the rest of the space about us and around us and for unfathomable distances beyond is cold, lifeless, and void. The nearest fixed star to us, on this minute scale, be it remembered,—the earth as a one-inch ball, and the moon a little pea—would be over 40,000 miles away.
The science that tells of these things and how men have come to know about them is Astronomy, and to books of astronomy the reader must go to learn more about the sun and stars. The science and description of the world on which we live are called respectively Geology and Geography.
The diameter of our world is a little under 8000 miles. Its surface is rough; the more projecting parts of the roughness are mountains, and in the hollows of its surface there is a film of water, the oceans and seas. This film of water is about five miles thick at its deepest part—that is to say, the deepest oceans have a depth of five miles. This is very little in comparison with the bulk of the world.
About this sphere is a thin covering of air, the atmosphere. As we ascend in a balloon or go up a mountain from the level of the sea-shore the air is continually less dense, until at last it becomes so thin that it cannot support life. At a height of twenty miles there is scarcely any air at all—not one hundredth part of the density of air at the surface of the sea. The highest point to which a bird can fly is about four miles up—the condor, it is said, can struggle up to that; but most small birds and insects which are carried up by aeroplanes or balloons drop off insensible at a much lower level, and the greatest height to which any mountaineer has ever climbed is under five miles. Men have flown in aeroplanes to a height of over four miles, and balloons with men in them have reached very nearly seven miles, but at the cost of considerable physical suffering. Small experimental balloons, containing not men, but recording instruments, have gone as high as twenty-two miles.
It is in the upper few hundred feet of the crust of the earth, in the sea, and in the lower levels of the air below four miles that life is found. We do not know of any life at all except in these films of air and water upon our planet. So far as we know, all the rest of space is as yet without life. Scientific men have discussed the possibility of life, or of some process of a similar kind, occurring upon such kindred bodies as the planets Venus and Mars. But they point merely to questionable possibilities.
Astronomers and geologists and those who study physics have been able to tell us something of the origin and history of the earth. They consider that, vast ages ago, the sun was a spinning, flaring mass of matter, not yet concentrated into a compact centre of heat and light, considerably larger than it is now, and spinning very much faster, and that as it whirled, a series of fragments detached themselves from it, which became the planets. Our earth is one of these planets. The flaring mass that was the material of the earth broke as it spun into two masses, a larger, the earth itself, and a smaller, which is now the dead, still moon. Astronomers give us convincing reasons for supposing that sun and earth and moon and all that system were then whirling about at a speed much greater than the speed at which they are moving to-day, and that at first our earth was a flaming thing upon which no life could live. The way in which they have reached these conclusions is by a very beautiful and interesting series of observations and reasoning, too long and elaborate for us to deal with here. But they oblige us to believe that the sun, incandescent though it is, is now much cooler than it was, and that it spins more slowly now than it did, and that it continues to cool and slow down. And they also show that the rate at which the earth spins is diminishing and continues to diminish—that is to say, that our day is growing longer and longer, and that the heat at the centre of the earth wastes slowly. There was a time when the day was not a half and not a third of what it is to-day; when a blazing hot sun, much greater than it is now, must have moved visibly—had there been an eye to mark it—from its rise to its setting across the skies. There will be a time when the day will be as long as a year is now, and the cooling sun, shorn of its beams, will hang motionless in the heavens.
It must have been in days of a much hotter sun, a far swifter day and night, high tides, great heat, tremendous storms and earthquakes, that life, of which we are a part, began upon the world. The moon also was nearer and brighter in those days and had a changing face.[1]
- ↑ For a convenient recent discussion of the origin of the earth and its early history before the seas were precipitated and sedimentation began, the student should consult Professor Burrell's contribution to the Yale lectures, The Evolution of the Earth and Its Inhabitants (1918), edited by President Lull.