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The progress in physics and geology requires a revision of geologic theories. We now know that the earth has a molten core, 4,000 miles in diameter, which is covered by a shell 1,800 miles thick, that is solid and mostly crystalline. It is called the mantle. And there is an outer crust 20 to 30 miles thick. The effective forces operating throughout this structure are gravity or load pressure, heat, and atomic attractions and repulsions. The heat may be attributed to compression and radioactive disintegration of atoms, but probably not to survival from an originally molten globe. In this hypothesis it is regarded as mainly due to radioactive processes.
It is reasonable to assume that radioactive minerals are present in the core and are its principle source of heat. Since the heat cannot escape the core must be heating and growing at the expense of the mantle. The earth is growing hotter, not cooling.
The boiling core emits gases and superheated liquids that bore into the mantle and form bubbles of magma. The bubbles rise by virtue of their bouyancy and boring activity. Their mineral composition changes by assimilation and adjustment of mineral species to environment. Starting from the core as nickel-iron and accessories they emerge in the crust as basalt and granite.
The mechanics of the pressure in and around a bubble of magma give it the shape of a pear, biggest at the top. On approaching the surface this effect develops the tack-shaped batholith. The cover over such a batholith is liable to uplift, indicated at the surface by elevated plateaus and broad domes or elongate swells, and to metamorphism, which may produce lateral pressures. The unbalanced load of an elevated mass also creates lateral pressure. Under certain circumstances the effect of lateral stress and strain in combination with magmatic heat may produce extensive horizontal intrusions 20 miles below the surface. Such a one is thought to have been the mass under the Appalachian geosyncline during the Paleozoic era. To that mobile foundation we may attribute the sinking of the sedim nts, and by a logical development of load stresses in combination with magmatic pressures we may explain the folding of the Appalachians, the outthrust of the Himalayas, and similar displacements.
Bubbles of igneous rock have risen to the surface at intervals during the last 2 billion years. They consist of two principle kinds, basalt and granite. They differ in fluidity or viscosity. The basalt reaches the surface and spreads out, forming such features as ocean beds and plateaus. The granite lifts the surface without breaking through, causes lateral stresses, and becomes the core of a mountain range. The possible mechanical effects are varied. We can not reason from one orogeny to another, without due consideration of the facts of unlike histories. The Appalachian mechanics will not explain the Rockies, or the Basin ranges, or the Alps. Each orogeny is a problem in itself. But they all are to be explained
through a study of the reactions of the forces of gravity, magmatic intrusion, and atomic activity.
The prolonged sequence of intrusions of the surface by magmatic bubbles is regarded as the source of the crust. The process is not finished or ever can be, since radioactive disintegration continues to heat the core. We may infer that the thinning mantle will ultimately disappear and the planet will become a star.
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