Abstract
The solar system formed in an already old Universe, which was about 10 Ga after the Big Bang. The earth accreted from dust and gas in the inner part of the solar nebula. Probably due to intense solar activity, volatile elements were rejected to the periphery of the nebula where giant planets (Jupiter, Saturn, Uranus, Neptune) formed, whereas terrestrial planets (Mercury, Venus, Earth and Mars) accreted in the relatively gas-poor region. Whatever the earth accretion process was (homogeneous vs. heterogeneous), it resulted in a shelled structure. All of the layers did not differentiate at the same time or by the same mechanism. It is now commonly admitted that the core-mantle differentiation occurred very early, before 4.5 Ga or even during the accretion event itself. Both accretion and core formation released more than 85% of the total earth energy.
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