Core–mantle differentiation

According to the Safronov's model,[3] protoplanets formed as the result of collisions of smaller bodies (planetesimals), which previously condensed from solid debris present in the original nebula.

The differentiation process is driven by the higher density of iron compared to silicate rocks, but the lower melting point of the former constitutes an important factor.

[1] On the premises of these plausible scenarios, several models have been proposed to account for the core-mantle differentiation following the stage of nebular formation of the Solar System.

[7] Experiments suggest that viscosity of the magma ocean was low, thereby implying turbulent convective flow that rapidly dissipates heat.

The equilibrium is found by the Weber number that provides a mean to calculate the stabilized diameter of the liquid iron droplets, which corresponds to 10 cm.

[1][5] Large iron blobs cannot be dragged by convective forces in the primordial mantle, therefore they do not have enough time to hydrodynamically equilibrate and reach the stabilized size.

From this stage on, iron aggregations triggered by Rayleigh-Taylor instabilities migrated through the primordial core in a long-term process (hundreds of million of years).

[12][2] One plausible scenario is that the primordial, cold silicate core fragmented in response to instabilities induced by the denser surrounding iron layer.

At the end, chunks of such a fragmented core ("rockbergs") migrated upward and incorporated into the mantle, whereas the iron alloy settled at the center of the Earth.

Hypothetical core-mantle differentiation processes: Percolation, diking, and diapirism. After Rubie et al. (2015). [ 1 ]
Alternative model for core-mantle differentiation: I. Melted iron layer between protomantle and primordial core. II. Primordial core cracking. III. Primordial core fragments. IV. Rockbergs ascend and iron forms new core. After Stevenson (1981). [ 2 ]