THE PLANET-FORMING ERA
Subsequent to the birth of our solar system a period of diminishing solar disgorgement ensued. Decreasingly, for another five hundred thousand years, the sun continued to pour forth diminishing volumes of matter into surrounding space. But during these early times of erratic orbits, when the surrounding bodies made their nearest approach to the sun, the solar parent was able to recapture a large portion of this meteoric material.
The planets nearest the sun were the first to have their revolutions slowed down by tidal friction. Such gravitational influences also contribute to the stabilization of planetary orbits while acting as a brake on the rate of planetary-axial revolution, causing a planet to revolve ever slower until axial revolution ceases, leaving one hemisphere of the planet always turned toward the sun or larger body, as is illustrated by the planet Mercury and by the moon, which always turns the same face toward our planet, Urantia. the earth will always turn the same hemisphere toward the moon, and the day and month will be analogous – in length about forty-seven days. When such stability of orbits is attained, tidal frictions will go into reverse action, no longer driving the moon farther away from the earth but gradually drawing the satellite toward the planet. And then, in that far distant future when the moon approaches to within about eleven thousand miles of the earth, the gravity action of the latter will cause the moon to disrupt, and this tidal- gravity explosion will shatter the moon into small particles, which may assemble about the world as rings of matter resembling those of Saturn or may be gradually drawn into the earth as meteors.
If space bodies are similar in size and density, collisions may occur. But if two space bodies of similar density are relatively unequal in size, then, if the smaller progressively approaches the larger, the disruption of the smaller body will occur when the radius of its orbit becomes less than two and one-half times the radius of the larger body. Collisions among the giants of space are rare indeed, but these gravity-tidal explosions of lesser bodies are quite common.
Shooting stars occur in swarms because they are the fragments of larger bodies of matter which have been disrupted by tidal gravity exerted by near- by and still larger space bodies. Saturn’s rings are the fragments of a disrupted satellite. One of the moons of Jupiter is now approaching dangerously near the critical zone of tidal disruption and, within a few million years, will either be claimed by the planet or will undergo gravity-tidal disruption. The fifth planet of the solar system of long, long ago traversed an irregular orbit, periodically making closer and closer approach to Jupiter until it entered the critical zone of gravity tidal disruption, was swiftly fragmentized, and became the present-day cluster of asteroids.
4,000,000,000 years ago, witnessed the organization of the Jupiter and Saturn systems much as observed today except for their moons, which continued to increase in size for several billions of years. In fact, all of the planets and satellites of our solar system are still growing as the result of continued meteoric captures.
3,500,000,000 years ago, the condensation nucleuses of the other ten planets were well formed, and the cores of most of the moons were intact, though some of the smaller satellites later united to make the present-day larger moons. This age may be regarded as the era of planetary assembly.
3,000,000,000 years ago, the solar system was functioning much as it does today. Its members continued to grow in size as space meteors continued to pour in upon the planets and their satellites at a prodigious rate. It is about this time our solar system was placed on the physical registry of our local universe Nebadon and given its name, Monmatia.
2,500,000,000 years ago, the planets had grown immensely in size. Our planet Urantia was a well-developed sphere about one-tenth its present mass and was still growing rapidly by meteoric accretion.
All of this tremendous activity is a normal part of the making of an evolutionary world on the order of our planet Urantia and constitutes the astronomic preliminaries to the setting of the stage for the beginning of the physical evolution of such worlds of space in preparation for its creature life adventure of time.
THE METEORIC ERA — THE VOLCANIC AGE ; THE PRIMITIVE PLANETARY ATMOSPHERE
Throughout these early times the space regions of the solar system were swarming with small disruptive and condensation bodies, and in the absence of a protective combustion atmosphere such space bodies crashed directly on the surface of Urantia. These incessant impacts kept the surface of the planet more or less heated, and this, together with the increased action of gravity as the sphere grew larger, began to set in operation those influences which gradually caused the heavier elements, such as iron, to settle more and more toward the center of our planet.
2,000,000,000 years ago, our earth began decidedly to gain on the moon. Always had Urantia been larger than its satellite, but there was not so much difference in size until about this time, when enormous space bodies were captured by the earth. Urantia was then about one fifth its present size and had become large enough to hold the primitive atmosphere which had begun to appear as a result of the internal elemental contest between the heated interior and the cooling crust. Definite volcanic action dates from these times. The internal heat of the earth continued to be augmented by the deeper and deeper burial of the radioactive or heavier elements brought in from space by the meteors. The study of these radioactive elements will reveal that our planet Urantia is more than one billion years old on its surface. The radium clock is our most reliable timepiece for making scientific estimates of the age of the planet, but all such estimates are too short because the radioactive materials open to our scrutiny are all derived from the earth’s surface and hence represent Urantia’s comparatively recent acquirements of these elements.
1,500,000,000 years ago, the earth was two-thirds its present size, while the moon was nearing its present mass. Earth’s rapid gain over the moon in size enabled it to begin the slow robbery of the little atmosphere which its satellite originally had.
Volcanic action is now at its height. The whole earth is a veritable fiery inferno, the surface resembling its earlier molten state before the heavier metals gravitated toward the center. This is the volcanic age. Nevertheless, a crust, consisting chiefly of the comparatively lighter granite, is gradually forming. The stage is being set for a planet which can someday support life.
The primitive planetary atmosphere is slowly evolving, now containing some water vapor, carbon monoxide, carbon dioxide, and hydrogen chloride, but there is little or no free nitrogen or free oxygen. The atmosphere of a world in the volcanic age presents a queer spectacle. In addition to the gases enumerated, it is heavily charged with numerous volcanic gases and, as the air belt matures, with the combustion products of the heavy meteoric showers which are constantly hurtling in upon the planetary surface. Such meteoric combustion keeps the atmospheric oxygen very nearly exhausted, and the rate of meteoric bombardment is still tremendous.
The atmosphere presently became more settled and cooled sufficiently to start precipitation of rain on the hot rocky surface of the planet. For thousands of years Urantia was enveloped in one vast and continuous blanket of steam. And during these ages the sun never shone upon the earth’s surface. Much of the carbon of the atmosphere was abstracted to form the carbonates of the various metals which abounded in the superficial layers of the planet. Later on, much greater quantities of these carbon gases were consumed by the early and prolific plant life.
Even in the later periods, the continuing lava flows and the incoming meteors kept the oxygen of the air almost completely used up. Even the early deposits of the soon appearing primitive ocean contain no colored stones or shales. And for a long time after this ocean appeared, there was virtually no free oxygen in the atmosphere; and it did not appear in significant quantities until it was later generated by the seaweeds and other forms of vegetable life.
The primitive planetary atmosphere of the volcanic age affords little protection against the collisional impacts of the meteoric swarms. Millions upon millions of meteors are able to penetrate such an air belt to smash against the planetary crush as solid bodies. But as time passes, fewer and fewer prove large enough to resist the ever-stronger friction shield of the oxygen-enriching atmosphere of the later eras.
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