The Earth is composed of four main layers - the crust, mantle, outer core and inner core. The crust ranges from 0-100km thick, the mantle ranges from 100-2900km thick, the outer core ranges from 2900-5100km thick and is liquid, and the inner core ranges from 5100-6378km thick and is solid. The main chemical components of the Earth are iron, oxygen, silicon, magnesium, nickel and sulfur.