But as there are many luminous comets of short period, they must have been produced or acquired at some time when other members of the system, the planets and the satellites, were already in their places. A theory has been offered that once the solar system moved through a nebula and obtained its comets there. 3H. N. Russell, The Solar System and Its Origin (1935), p.
40.
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Did the sun emit planets by shrinkage or by tide, and comets by explosion? Did the comets come from interstellar space and were they captured into the solar system by larger planets? Did the larger planets produce the smaller planets by cleavage, or did they expel the short-period comets from their bodies?
It is admitted that we cannot know the truth about the origin of the planetary and cometary systems billions of years ago. "The problem of the origin and development of the solar system suffers from the label 'speculative.' It is frequently said that as we were not there when the system was formed, we cannot legitimately arrive at any idea of how it was formed." * The most we can do, it is believed, is to investigate one planet, the one under our feet, in order to learn its past; and then, by the deductive method, to apply the results to other members of the solar system.
4 Harold Jeffreys, "The Origin of the Solar System" in Internal Constitution of the Earth, B.
Gutenberg, ed. (1939).
CHAPTER 2
The Planet Earth
THE PLANET earth has a stony shell—the lithosphere; it consists of igneous rock, like granite and basalt, with sedimentary rock on top. The igneous rock is the original crust of the earth; sedimentary rock is deposited by water.
The inner composition of the earth is not known. The propagation of seismic waves gives support to the assumption that the shell of the earth is over 2,000 miles thick; on the basis of the gravitational effect of mountain masses (the theory of isostasy), the shell is estimated to be only sixty miles thick.
The presence of iron in the shell or the migration of heavy metals from the core to the shell has not been sufficiently explained. For these metals to have left the core, they must have been ejected by explosions, and in order to remain spread through the crust, the explosions must have been followed immediately by cooling.
If, in the beginning, the planet was a hot conglomerate of elements, as the nebular as well as the tidal theories assume, then the iron of the globe should have become oxidized and combined with all available oxygen. But for some unknown reason this did not take place; thus the presence of oxygen in the terrestrial atmosphere is unexplained.
robin-bobin
The water of the oceans contains a large amount of soluble sodium chloride, common salt.
Sodium might have come from rocks eroded by rain; but rocks are poor in chlorine and the proportion of sodium and chlorine in sea water calls for fifty times more chlorine in the igneous rock than it actually contains.
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The deep strata of igneous rock contain no signs of fossil life. Incased in sedimentary rock are skeletons of marine and land animals, often in many layers one upon the other. Not infrequently igneous rock is found protruding into sedimentary rock or even covering it over large areas, pointing to successive eruptions of igneous rock that became heated and molten after there was life on the earth.
Upon strata which show no signs of fossil life are strata containing shells, and sometimes the shells are so numerous as to constitute the entire mass of the rock. They are often found in the hardest rock. Higher strata contain skeletons of land animals, often of extinct species, and not infrequently, above the strata with the remains of land animals are other strata with marine fauna.
The species of the animals, and even their genera, change with the strata. The strata often assume an oblique position, sometimes being almost vertical; frequently they are faulted and overturned in many ways.
Cuvier (1769-1832), the founder of vertebrate paleontology, or the science of petrified skeletons of animals possessing vertebrae, from fish to man, was much impressed by the picture presented by the sequence of the layers of earth.
"When the traveller passes over these fertile plains where gently flowing streams nourish in their course an abundant vegetation, and where the soil, inhabited by a numerous population, adorned with flourishing villages, opulent cities, and superb monuments, is never disturbed, except by the ravages of war, or by the oppression of the powerful, he is not led to suspect that Nature also has had her intestine wars, and that the surface of the globe has been broken up by revolutions and catastrophes. But his ideas change as soon as he digs into that soil which now presents so peaceful an aspect." 1
Cuvier thought that great catastrophes had taken place on this earth, repeatedly changing sea beds into continents and continents into sea beds. He held that genera and species were unchangeable since Creation; but, observing different animal remains in various levels of earth, he concluded that catastrophes must have annihilated
1 G. Cuvier, Essay on the Theory of the Earth (5th ed., 1827) (English transl. of Discours sur les revolutions de la surface du globe, et sur les changements qu'elles ont produits dans le resne animal).
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life in vast areas, leaving the ground for other forms of life. Where did these other genera come from? Either they were newly created or, more likely they migrated from other parts of the world, which were not at that time also visited by cataclysms.
He could not find the cause of these cataclysms. He saw in their traces "the problem in geology it is of most importance to solve," but he realized that "in order to resolve it satisfactorily, it would be necessary to discover the cause of these events—an undertaking which presents a difficulty of quite a different kind." He knew only of "many fruitless attempts" already made and he did not find himself able to offer a solution. "These ideas have haunted, I may almost say have tormented me during my researches among fossil bones." 2
Cuvier's theory of stabilized forms of life and of annihilating catastrophes was supplanted by a theory of evolution in geology (Lyell) and biology (Darwin). The mountains are what is left of plateaus eroded by wind and water in a very slow process. Sedimentary rock is detritus of igneous rock eroded by rain, then carried to sea, and there slowly deposited. Skeletons of birds and of land animals in these rocks are presumed to have belonged to animals that waded close to the shore of the sea in shallow water, died while wading, and were covered by sediment before fish destroyed the cadavers or the water separated the bones of their skeletons. No widespread robin-bobin
catastrophes disrupted the slow and steady process. The theory of evolution, which can be traced to Aristotle, and which was the teaching of Lamarck in the days of Cuvier and of Darwin after him, has been generally accepted as truth by natural sciences for almost a hundred years.
Sedimentary rock covers high mountains and the highest of all, the Himalayas. Shells and skeletons of sea animals are found there. This means that at some early time fish swam over these mountains. What caused the mountains to rise?
A force pushing from within or pulling from without or twisting on the sides must have elevated the mountains and lifted continents from the bottom of the sea and submerged other land masses.
If we do not know what these forces are, we cannot answer the problem of the origin of the mountains and of continents, wherever 3 Ibid., pp. 240-242.