The Sun, Earth and other planets of our Solar System formed by condensation and aggregation of matter from a protoplanetar disc, 4.567 to 4.563 Ga ago. Heat from the decay of a huge number of short lived nuclides (²⁶Al and many others) along with nascent gravitational energy lead to very high temperatures on the Proto-Earth. It is therefore likely that the Proto-Earth was more or less a fully molten melange of iron and silicate melt. Due to liquid immiscibility and the high density of iron, the Earth's core formed by gravitational segregation. From tungsten isotopes it is known that this core forming process was early in Earth's history, within ~30 Ma after the beginning of the solar system (Kleine et al. 2002). The remaining silicate part of the Earth is called bulk silicate Earth (BSE) or primitive or primordial mantle (PRIMA). Its chemical composition for lithophile and refractory elements can be estimated from the composition of chondritic meteorites, by volumetrically balancing their silicate and iron parts.

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Kleine, T., Münker, C., Mezger, K. & Palme, H., 2002, Rapid accretion and early core formation on asteroids and the terrestrial planets from Hf–W chronometry. Nature, 418, 952-955.