Final answer:
Earth's core is mainly composed of iron, accounting for about 85%, with nickel making up most of the remaining 15%, alongside substantial quantities of sulfur, all at a very high density.
Step-by-step explanation:
The Earth's core is composed mainly of iron and nickel. This conclusion is based on several lines of evidence. First, the overall density of the planet, as calculated from its rotation, suggests that the interior must be denser than the surface layers, leading to the conclusion that the core consists of heavy metals. Calculations indicate the core contains about 85% iron and 15% nickel. Additionally, metallic meteorites, which are thought to resemble the composition of Earth's core, also mirror this iron/nickel ratio.
Earth's core is differentiated into a liquid outer core and a solid inner core, the latter of which is thought to be composed of an iron-nickel alloy due to the immense pressure at that depth. Besides iron, the core also contains significant amounts of nickel and sulfur, compressed to a high density. The properties of Earth's core are further understood through the analysis of seismic waves, which provide a picture of the interior composition based on how these waves travel through different materials.