Centennial by James A. Michener Read Free Book Online

bells” sounded over the telephone—three male voices, joined later by a soprano. It would be an interesting time till Christmas.

Chapter 2

THE LAND
    When the earth was already ancient, of an age incomprehensible to man, an event of basic importance occurred in the area which would later be known as Colorado.
    To appreciate its significance, one must understand the structure of the earth ( See Map 02 – Structure of Earth ) , and to do this, one must start at the vital center.
    Since the earth is not a perfect sphere, the radius from center to surface varies. At the poles it is 3950 miles and at the equator 3963. At the time we are talking about, Colorado lay about the same distance from the equator as it does now, and its radius was 3956. Those miles were composed in this manner.
    At the center then, as today, was a ball of solid material, very heavy and incredibly hot, made up mostly of iron; this extended for about 770 miles. Around it was a cover about 1375 miles thick, which was not solid, but which could not be called liquid either, for at that pressure and that temperature, nothing could be liquid, as we know that word. It permitted movement, but it did not easily flow. It transmitted heat, but it did not bubble. It is best described as having characteristics with which we are not familiar, perhaps like a warm plastic.
    Around this core was fitted a mantle of dense rock 1784 miles thick whose properties are difficult to describe, though much is known of them. Strictly speaking, this rock was in liquid form, but the pressures exerted upon it were such as to keep it more rigid than a bar of iron. The mantle was a belt which absorbed both pressure and heat from many directions and was, consequently, under considerable stress. From time to time throughout this story, the pressures will become so great that some of the mantle material will force its way toward the surface of the earth, undergoing marked change in the process. The resultant body of molten liquid, called magma, will solidify to produce the igneous rock, granite, but if it is still in liquid form as it approaches the surface, lava results. It was in the mantle that many of the movements originated which would determine what was to happen next to the visible structure of the earth, and although we shall not often refer again to the mantle, we must remember it deep beneath our feet, accumulating stress and generating enormous heat as it prepares for its next dramatic excursion toward the surface, producing the magma which will appear as either granite or lava.
    At the top of the mantle, only twenty-seven miles from the surface, rested the earth’s crust, where life would develop. What was it like? It can be described as the hard scum that forms at the top of a pot of boiling porridge. From the fire at the center of the pot, heat radiates not only upward, but in all directions. The porridge bubbles freely at first when it is thin, and its motion seems to be always upward, but as it thickens, one can see that for every slow bubble that rises at the center of the pan, part of the porridge is drawn downward at the edges; it is this slow reciprocal rise and fall which constitutes cooking. In time, when enough of this convection has taken place, the porridge exposed to air begins to thicken perceptibly, and the moment the internal heat stops or diminishes, it hardens into a crust.
    This analogy has two weaknesses. The flame that keeps the geologic pot bubbling does not come primarily from the hot center of the earth, but rather from the radioactive structure of the rocks themselves. And as the liquid magma cools, different types of rock solidify: heavy dark ones rich in iron settle toward the bottom; lighter ones like quartz move to the top.
    The crust was divided into two distinct layers. The lower and heavier, twelve miles thick, was composed of a dark, dense rock known by the made-up name of sima, indicating the predominance of silicon and magnesium. The upper