Yes, the Earth´s core is made of about 85% iron, 5% nickel and 10% lighter elements. The crust is about 47% oxygen and 28% silicon; oxygen, silicon, aluminum, iron, calcium, sodium, potassium and magnesium make up another 24%; and other elements make up the remaining 1.5%. The bulk composition of the entire Earth reflects the abundance of elements in the early solar system, just with less hydrogen and helium. The Earth, as well as the other rocky planets and asteroids, formed through the collision of smaller bodies early in the solar system´s history. The early Earth was heated up by several processes, including (1) the radioactive decay of uranium, thorium, an potassium-40, (2) the conversion of gravitational energy into heat energy during the gravitational compaction of the Earth, and (3) heating from large meteorite impacts. Once the Earth heated up to the melting temperature of iron, the heavy iron was pulled into the center of the Earth, forming the Earth´s core. The lighter elements, like oxygen and silicon, moved upwards toward the Earth´s surface, forming the Earth´s mantle and crust.