The rocky and metallic planetesimals in the inner solar system form into Earth-like planets with molten interiors. As these Earth-like planets radiate the heat of compression into space, they form hard crusts. Over long periods of time, they may become solid all the way through. Bombardment by rocky and icy planetesimals disrupts the surface but also delivers elements and molecules, including -- most critically from the standpoint of the evolution of life -- water.
Predominantly icy objects in the outer solar system form Jupiter-like planets. With or without a rock and metal core, these planets are mostly liquid surrounded by thick gaseous layers; the composition of a Jupiter-like planet is similar to that of its star. These planets, too, are subject to frequent impact by icy and rocky objects.