Centennial by James A. Michener Read Free Book Online Page A

and lighter layer, fifteen miles thick, was composed of lighter rock known by the invented word sial, indicating silicon and aluminum. The subsequent two miles of Colorado’s rock and sediment would eventually come to rest on this sialic layer.
    Three billion, six hundred million years ago the crust had formed, and the cooling earth lay exposed to the developing atmosphere. The surface as it then existed was not hospitable. Temperatures were too high to sustain life, and oxygen was only beginning to accumulate. What land had tentatively coagulated was insecure, and over it winds of unceasing fury were starting to blow. Vast floods began to sweep emerging areas and kept them swamp-like, rising and falling in the agonies of a birth that had not yet materialized. There were no fish, no birds, no animals, and had there been, there would have been nothing for them to eat, for grass and trees and worms were unknown.
    There were in existence, even under these inhospitable conditions, elements like algae from which recognizable life would later develop, but the course of their future development had not yet been determined.
    The earth, therefore, stood at a moment of decision: would it continue as a mass with a fragile covering incapable of sustaining either structures or life, or would some tremendous transformation take place which would alter its basic surface appearance and enlarge its capacity?
    Sometime around three billion, six hundred million years ago, the answer came. Deep within the crust, or perhaps in the upper part of the mantle, a body of magma began to accumulate. Its concentration of heat was so great that previously solid rock melted partially. The lighter materials were melted first and moved upward through the heavier material that was left behind, coming to rest at higher elevations and in enormous quantities.
    Slowly but with irresistible power it broke through the earth’s crust and burst into daylight. In some cases, the sticky, almost congealed magma may have exploded upward as a volcano whose ash would cover thousands of square miles, or, if the magma was of a slightly different composition, it would pour through fissures as lava, spreading evenly over all existent features to a depth of a thousand feet.
    As the magma spread, the central purer parts solidified into pure granite. Most of it, however, was trapped within the crust, and slowly cooled and solidified into rock deep below the surface.
    What degree of time was required for this gigantic event to complete itself? It almost certainly did not occur as a vast one-time cataclysm although it might have, engulfing all previous surface features in one titanic wrenching which shook the world. More likely, convective movements in the mantle continued over millions of years. The rising internal heat accumulated eon after eon, and the resultant upward thrust still continues imperceptibly.
    The earth was at work, as it is always at work, and it moved slowly. A thousand times in the future this irresistible combination of heat and movement would change the aspect of the earth’s surface.
    This great event of three billion, six hundred million years ago was different from many similar events for one salient reason: it intruded massive granite bodies which, when the mountains covering it were eroded away, would stand as the permanent basement rock. In later times it would be penetrated, wrenched, compressed, eroded and savagely distorted by cataclysmic forces of various kinds. But through three billion, six hundred million years, down to this very day, it would endure. Upon it would be built the subsequent mountains; across it would wander the rivers; high above its rugged surface animals would later roam; and upon its solid foundations homesteads and cities would rest.
    A relatively short distance below the surface of the earth it rides, this infinitely aged platform, this permanent base for action. How do we know of its existence? From time to time, in