Earth's core

“ All these manifestations of heat are derived from the great stores which exist in the interior of the earth. The consideration of them and of the known increase of temperature with depth led earlier geologists to believe that the earth possessed a heated molten core and a cold and relatively thin exterior shell. But as further investigation developed correct conceptions of the rigidity of the globe in resisting strains produced by its rotation and the attraction of other heavenly bodies for its mass ”

“ According to the account now generally accepted, the original material of the earth seems to have been a semi-solid or semi-fluid mass formed by the condensation of the still more fluid or even gaseous nebula out of which all the planets of the solar system have been formed and of which the sun is the still fiery core. ”

“ In the system of the globe every thing must be consistent. The changing and destroying operations of the surface exposed to the sun and influences of the atmosphere, must correspond to those by which land is composed at the bottom of the sea; and the consolidating operations of the mineral region must correspond to those appearances which in the rocks, the veins, and solid stones, give such evident, such universal testimony of the power of fire, in bringing bodies into fusion, or introducing fluidity, the necessary prelude to solidity and concretion. ”

“ These are the considerations which are held to prove that the inorganic structure of the globe through all its successive stages—the earth beneath our feet, with its varied surface of land and sea, mountain and plain, and with its atmosphere which distributes heat and moisture over that surface—has been evolved as the necessary result of the original aggregation of matter at some extremely remote period, and of the subsequent modification of that matter in condition and form under the exclusive operation of invariable physical forces. ”

“ The same elements, the same principles, are found in the formation of minerals, as well as in their decomposition, whether natural or artificial. We find that earth, diversely modified, wrought, and combined, serves to increase their bulk, and give them more or less density and gravity. Air and water contribute to make their particles cohere; the igneous matter, or inflammable principle, tinges them with colour, and sometimes plainly indicates its presence, by the brilliant scintillation which motion elicits from them. ”

“ We thus are led to inquire into the efficient causes of this constitution of things, by which solidity and stability had been bestowed upon a mass of loose materials, and by which this solid earth, formed first at the bottom of the sea, had been placed in the atmosphere, where plants and animals find the necessary conditions of their life. ”

“ The material portion of the earth is altogether a surface film, an insignificant skin over the sphere of purity, the center of gravitation. Although men naturally imagine that the density and stability of the earth is dependent on the earthy particles, of which his own body is a part, such is not the case. Earth, as man upon the outer surface, can now know it, is an aggregation of material particles, a shell resting on this globular sphere of medial force, which attracts solid matter from both the outer and inner surfaces of earth, forming thereby the middle of the three concentric spheres. ”

“ I shall answer, by the same causes, and by the same means as it exists on the terrestrial globe, although composed of stone, gres, marble, iron, and glass. There are other planets like our globe, whose principal is one of these matters; but the external causes will soon have altered its superficial strata, and according to the different degrees of heat or cold, dryness or humidity, they will have converted this matter into a fertile earth proper to receive the seeds of organized nature, which only needs heat and moisture to develope itself. ”

“ With the separation of the ore and the Inflammable out of the primary water and the confluence of the Earthy into marine salt, its metamorphosis upon the surface or when exposed to light is at an end. All forms of the planet have been successively developed out of the earth-element. It can attain no further to anything new, and if nature had not yet been concluded, that which in the sequel is still dynamically developed upon our earth, must be thus a product, which extends beyond the mineral kingdom. ”

“ A dewdrop on the petal of a flower is nearly globular; but it is not quite a globe, because the gravitation presses it against the flower and somewhat distorts the shape. A falling drop of rain is a globe; a drop of oil suspended in a liquid with which it does not mix forms a globe. Passing from small things to great things, let us endeavour to conceive a stupendous globe of molten matter. Let that globe be as large as the earth, and let its materials be so soft as to obey the forces of attraction exerted by each part of the globe on all the other parts. ”

“ Lifting our searching gaze into the measureless space beyond our earth, we find planet bound to planet, and system chained to system, all impelled by a universal force to roll in regularity and order around a common centre. The pendulations of the remotest star are communicated through the unseen bond; and our rocking world obeys the mysterious impulse throughout all those forces which regulate the inorganic combinations of this earth, and unto which its organic creation is irresistibly compelled to bow. ”

“ Passing by his speculations on the displacement of the poles of the earth, and on the elevations of the equatorial regions, which will dispense with the necessity of considering the earth as originally in a liquid condition, he allows that “the terrestrial globe is not at all a body entirely and truly solid, but that it is a combination (réunion) of bodies more or less solid, displaceable in their mass or in their separate parts, and among which there is a great number which undergo continual changes in condition.” ”

“ Abstracting them from the investigations before us, we arrive at the idea of the earth in its first condition as a globe of its present size—namely, as a mass, externally at least, consisting of the crystalline kind of rock, with the waters of the present seas and the present atmosphere around it, though these were probably in considerably different conditions, both as to temperature and their constituent materials, from what they now are. ”

“ In Cordier’s purely thermometrical theory as to the nature and mode of action of the great elevating force that has at successive periods raised and broken the earth’s crust, lifting up various igneous or plutonic rocks, and forcing them into the cracks and fissures, the central nucleus of the earth is considered in the light of an immense sea of molten mineral matter. ”

“ In this cooling down and solidification of the Earth’s surface, we have one of the simplest, as well as one of the most important, instances, of that change from a uniform to a multiform state which occurs in any mass through exposure of its different parts to different conditions. To the differentiation of the Earth’s exterior from its interior thus brought about, we must add one of the most conspicuous differentiations which the exterior itself afterwards undergoes, as being similarly brought about. ”

“ Similarly, the later planets disengaged would acquire a large proportion of the substances which form solid rocks. In the case of the earth we may suppose that the greater part was rock-making material, since the earth’s specific gravity is so high ”

“ But it is likewise the creed adopted by other distinguished geologists, that the interior of the globe is neither gas nor water, nor any of the heaviest minerals known, for in none of these cases would the earth weigh what it does. ”

“ Even now our knowledge carries us far enough to warrant the assertion that there was a time when our earth was in a state of igneous fusion, when no ocean bathed it and no atmosphere surrounded it, when no wind blew over it and no rain fell upon it, but an intense heat held all its materials in solution. In those days the rocks which are now the very bones and sinews of our mother Earth—her granites, her porphyries, her basalts, her syenites—were melted into a liquid mass. ”

“ The regulation which disposes the arrangements of matter on this earth, must exist through the celestial spaces, and every planet bears the same relation to every other glittering mass in heaven’s o’erarching canopy, as one atom bears to another in the pebble, the medusa, the lion, or the man. An indissoluble bond unites them all, and the grain of sand which lies buried in the depth of one of our primary formations, holds, chained to it by these all-pervading forces, the uncounted worlds which, like luminous sand, are sprinkled by the hand of the Creator through the universe. ”

“ Hence it was a common opinion among the older Geologists that the condition of our globe is that of a vast central nucleus composed of molten mineral, and covered over with a comparatively thin external shell of solid rock. The most eminent Geologists, however, of the present day, hesitate to accept this opinion. They observe: (1) That we have not yet learned what the material is of which the interior of the Earth is composed; therefore we cannot tell for certain what degree of heat is sufficient to reduce that material to a liquid state. ”

“ We see that while the geological changes classed as igneous, result from the still-progressing motion of the Earth’s substance to its centre of gravity; the antagonistic changes classed as aqueous, result from the still-progressing motion of the Sun’s substance towards its centre of gravity—a motion which, transformed into heat and radiated to us, is here re-transformed, directly into motions of the gaseous and liquid matters on the Earth’s surface, and indirectly into motions of the solid matters. ”

“ Let us suppose that during the period required by any of the speculations of geologists, however long, a mass of matter was gathered in an unformed condition, and gradually shaped into the present condition of the earth by the action of its constituent elements upon each other, influenced by the laws of mechanical forces, of chemical combinations, of light and heat, and of whatever physical agencies were made to operate in the process of evolving the mass into the condition in which it has been known to us for a certain time. ”

“ But within the mass, slowly and silently, the force of gravitation is compressing the particles in its giant hand, and gathering the denser toward the centre, while heat is given forth on all sides from the condensing mass into the voids of space without. Little by little the denser and less volatile matters collect in the centre as a fluid molten globe, the nucleus of the future planet; and in this nucleus the elements, obeying their chemical affinities hitherto latent, are arranging themselves in compounds which are to constitute the future rocks. ”

“ From all this we obtain, as the most probable solution of the problem of the constitution of the interior parts of the earth, that the substances therein occurring have such analogies to those now seen near the surface, that they would have been subjected to very much greater condensation than they have suffered,—the globe would have been denser than it is,—were it not for the expansive influence of heat in the interior of the planetary mass. ”

“ Apparently the forces of the molecular, atomic, and sub-atomic attractions increase at higher rates, and have individual peculiarities of action quite different from gravity. It would be of the utmost service to geological philosophy if these laws of molecular and sub-molecular attractions were firmly established, and could be applied to the conditions of heat and pressure under which the matter of the interior of the earth exists. ”

“ Further, it seems to have been rendered probable, from the density of rocky matter in the solid and liquid states, that a molten globe would solidify at the centre as well as at the surface, and consequently that the earth must not only have a solid crust of great thickness, but also a solid nucleus, and that any liquid portions must be of the nature of a sheet or of detached masses intervening between these. ”

“ By laws, the origin of which we have not yet traced, the condition of the diffused heat was changed, and the particles of the gaseous matter, condensed and agglomerated by attraction, into a series of planets, of which our earth is the third in point of size. That the earth has undergone vast changes, is evident to the most superficial geological student. ”

“ Even the earth itself is composed, as geologists tell us, of various strata, composed of different substances, and varying from one degree of density to another. If every part of our globe be regulated according to the received laws of gravity, and the relative density of matter, why do we find almost all over the world, light alluvial soil in the vallies and [55] plains; and on the tops of the highest mountains, the more heavy granite, and some of the heaviest substances that nature knows? ”

“ So far it seemed necessary to premise with regard to the great mineral power which we are to employ as an agent in the system of this earth; and it may be now observed, that it is in the proper relation of this power of heat and the fluidity or softness of bodies, as cause and effect, that we are to find a physical principle or argument for detecting those false theories of the earth that have been only imagined, and not properly founded on fact or observation. ”