Earth's core is primarily made up of iron (Fe), with a smaller percentage of nickel (Ni).

Here's a breakdown:

* Outer Core: Liquid, primarily iron and nickel with smaller amounts of sulfur, silicon, and oxygen. It's about 2,200 kilometers (1,367 miles) thick.

* Inner Core: Solid, primarily iron and nickel with a small percentage of other elements. It's about 1,220 kilometers (758 miles) thick.

While iron and nickel are the dominant elements, the core also contains trace amounts of other elements, making its composition incredibly complex.