Final answer:
Yes, terrestrial planets were initially molten or partially molten, which allowed iron and other heavy metals to sink to the center, a process known as planetary differentiation.
Step-by-step explanation:
The main answer to whether terrestrial planets were initially molten or partially molten and if the iron sunk to the center is: Yes. During the early stages of the solar system, the terrestrial planets, including Earth, Mars, Venus, and Mercury, underwent a phase known as planetary differentiation. This was a process where their internal structures formed with dense metals at the core and lighter silicates near the surface. This differentiation occurred because the planets were once hot enough to be molten, allowing heavier elements like iron to sink towards the center due to gravity. As the planets accreted from the collisions of planetesimals, the energy from these impacts contributed to the melting of their interiors. The molten state facilitated the separation of materials based on density, leading to the formation of metallic cores and rocky mantles.In conclusion, the early molten state of terrestrial planets was essential for the differentiation process, allowing iron and other heavy metals to migrate to the center and form the planets' cores.