The term 'Part of the Earth's Crust' can be summarized by two crossword solutions: PLATE (5 letters) and Sial (4 letters). PLATE is a large, rigid slab of solid rock that forms part of the Earth's lithosphere. It is composed of oceanic and continental crusts and is the outermost layer of the Earth's surface. Sial is the uppermost layer of the Earth's crust, composed of silica and aluminum-rich rocks such as granite and gneiss. It is the most abundant layer of the Earth's crust and is found beneath the oceanic crust.