Final answer:
Our solar system formed from a solar nebula, with the inner planets made of rock and metal due to high heat, and the outer planets containing more gas and ice. The solar nebula's collapse created a disk where planetesimals formed, eventually evolving into the current solar system.
Step-by-step explanation:
The formation of our solar system began around 4.5 billion years ago with a solar nebula, a giant, spinning cloud of gas and dust. The solar nebula collapsed under its own gravity, leading to an increase in temperature at the center and causing most of the solid material to vaporize. As it shrank and flattened into a disk, the cooler parts away from the center allowed solid particles to condense into planetesimals, which are the building blocks of planets and moons.
Terrestrial and Giant Planet Formation
The inner planets, or terrestrial planets, formed closer to the Sun where it was too hot for gases and ices to survive, resulting in rocky and metallic compositions. The giant planets formed further out, in the cooler regions of the disk, enabling them to capture and retain hydrogen and helium from the nebula, thus having a composition closer to the Sun. The difference in temperature within the solar nebula is the primary reason the inner and outer planets have distinct compositions.
Further Evolution of the Solar System
Post-formation, the solar system continued to evolve. The process of accretion caused differentiation and heating of planets, and the solar wind from the young Sun cleared lighter gases. Planetesimals that didn't form into planets became comets and asteroids, while violent impacts over millions of years swept up debris, leading to the current structure of our solar system.