Final answer:
Terrestrial planets formed in two main steps: condensation and clustering of grains to form planetesimals, followed by accretion and heating which led to planetary differentiation.
Step-by-step explanation:
Formation of Terrestrial Planets
The formation of terrestrial planets involved two main steps. Initially, dust grains in the solar nebula condensed and clumped together to form larger solid chunks called planetesimals, which are a few kilometers to a few tens of kilometers in diameter. These planetesimals can still be observed today as comets and asteroids. To transition from a planetesimal to a full-fledged planet, a significant increase in size was necessary.
Following the planetesimal stage, accretion played a significant role in the growth of these celestial bodies. Each protoplanet grew by continually attracting and incorporating more planetesimals. This accumulation and the resulting high-energy impacts led to the heating and melting of the protoplanets, eventually causing planetary differentiation.
During this process, heavier materials like metals sank to the core, while lighter silicates floated to the surface. Furthermore, due to heating, the inner protoplanets lost lighter gases, enriching them in heavier elements and compounds.
After these formative processes, the planets cooled and their surfaces were frequently cratered by debris impacts. Over time, the acquisition of volatile materials ceased, and the planets started their unique evolutionary paths, shaping their current aspects and properties.