AP BIOLOGY

Detailed explanation-1: -The inner core is at the center of the Earth because it is the densest, made of solid iron and nickel.

Detailed explanation-2: -Unlike the mineral-rich crust and mantle, the core is made almost entirely of metal-specifically, iron and nickel. The shorthand used for the core’s iron-nickel alloys is simply the elements’ chemical symbols-NiFe. Elements that dissolve in iron, called siderophiles, are also found in the core.

Detailed explanation-3: -The outer core is about 1, 400 miles thick, and it’s made mostly of a combination (called an alloy) of iron and nickel, along with small amounts of other dense elements like gold, platinum, and uranium. These metals can, of course, be found on the surface of Earth in solid form.

Detailed explanation-4: -Now that the Earth has cooled somewhat, pressure deep in the Earth increases local density by forcing liquids (e.g. the liquid outer core) into a solid state (the solid inner core), and then as the pressure increases, solids shift into new, more tightly packed crystal structures.