Final answer:
The direct answer is that the terrestrial planets formed an iron core first and a silicate crust later, due to the process of differentiation during the phase when these planets were molten.
Step-by-step explanation:
If the terrestrial planets were formed by homogeneous accretion, the direct answer to the question is: They formed an iron core first and a silicate crust later. The explanation for this process begins with the fact that during the early stages of the solar system, the inner planets including Earth, Venus, Mars, and Mercury, went through a phase where they were hot enough to be molten. This phase allowed for the process of differentiation, where denser materials such as metals sank towards the center (forming an iron core) and lighter materials such as silicates floated towards the surface, forming a crust.
As they grew in size, the larger protoplanets would have heated up due to impacts, causing planetary differentiation. This process would have led to the formation of an iron core in the center and a silicate crust on the surface of the terrestrial planets.This process would have excluded much of the lighter materials like hydrogen, which are more abundant in the Jovian planets due to their different formation processes. Consequently, the terrestrial planets have a quite different composition, being rich in heavier elements like iron and silicon, rather than the hydrogen and heliun-rich composition of the Jovian planets.