معدن الحديد مُنَزّلٌ من الفضاء الخارجي – المراجع العلمية

ENCYCLOPEDIA BRITANNICA:

“… The origin of the Earth by the accretion of planetesimals is a well-founded hypothesis, however, and meteorites are probably examples of planetesimals that have survived from the preplanetary stage of the solar system. It thus seems likely that the Earth formed by the accretion of solid bodies with the average composition of stony meteorites. The accretion process, however, led to massive segregation of the elements. Much of the iron was reduced to the metallic state and sank to the centre to form the core, carrying with it the major part of the siderophile elements. Lithophile elements, those with a greater affinity for oxygen than iron, combined as oxide compounds, mostly silicates, and provided material for the mantle and crust. Chalcophile elements would tend to form sulfides; however, few sulfides are stable at the high temperatures of the Earth's interior, so the fate of the chalcophile elements during the early history of the Earth is somewhat uncertain.

This primary geochemical differentiation of the Earth can be interpreted in terms of the system iron-magnesium-silicon-oxygen-sulfur, because these five elements make up about 95 percent of the Earth. There was insufficient oxygen to combine with the major metallic elements iron, magnesium, and silicon; because magnesium and silicon have a greater affinity for oxygen than iron, these elements combined completely with oxygen, and the remaining oxygen combined with part of the iron, leaving the remainder as the metal iron and iron sulfide. As indicated above, the metal sank to form the core, carrying with it the major part of the siderophile elements...”

“… Further heating of the material leads to a complicated set of nuclear reactions whereby the elements produced in carbon and oxygen burning are gradually converted into the elements of maximum fractional binding energy; e.g., chromium, manganese, iron, cobalt, and nickel. These reactions have collectively been given the name silicon burning because an important part of the process is the breaking down of silicon nuclei into helium nuclei, which are added in turn to other silicon nuclei to produce the elements noted above.

Finally, at temperatures around 4 109 K, an approximation to nuclear statistical equilibrium may be reached. At this stage, although nuclear reactions continue to occur, each nuclear reaction and its inverse occur equally rapidly, and there is no further overall change of chemical composition. Thus, the gradual production of heavy elements by nuclear fusion reactions is balanced by disintegrations, and the buildup process effectively ceases once the material is predominantly in the form of iron and its neighbouring elements of the periodic table. Indeed, if further heating occurs, a conversion of heavy nuclei to light nuclei follows in much the same way as occurs in the ionization of atoms when they are heated up. The elements heavier than iron cannot be produced by fusion reactions between light elements; an input of energy is required to produce them…”

“… The density at the Sun's core is about 100 times that of water (roughly six times that at the centre of the Earth), but the temperature is at least 15,000,000 K, so the central pressure is at least 10,000 times greater than that at the centre of the Earth, which is 3,500 kilobars.

While the temperature of the Sun drops from 15,000,000 K at the centre to 5,800 K at the photosphere, a surprising reversal occurs above that point; the temperature drops to a minimum of 4,000 K, then begins to rise in the chromosphere, a layer about 7,000 kilometres high at a temperature of 8,000 K…”

“… For very low-mass stars, the maximum temperature may be too low for any significant nuclear reactions to occur, but for stars as massive as the Sun or greater, most of the sequence of nuclear fusion reactions described above can occur. Moreover, a time scale for stellar evolution is derived in theories of stellar evolution that show that stars substantially more massive than the Sun can have completed their active life history in a time short compared with the age of the universe derived from the big-bang cosmological theory.

This result implies that stars more massive than the Sun, which were formed very early in the life history of the Galaxy, could have produced some of the heavy elements that are seen today but that stars much less massive than the Sun could have played no part in this production…”

“Iron which is the chief constituent of the earth’s core, is the most abundant element in the earth as a whole (about 35 percent) …”.