The core and mantle.
The core and mantle together make up the main body of the earth. except from the upper mantle they are to deep to be studied with direct tests. This means that our understanding of them has to come from indirect studies such as rock density comparisons and monitoring seismic waves that travel trough the earth. Together all of this data has led us to believe that there is a metallic core. This consists of a solid centre with liquid outer layers that are definitely separated from the solid mantle rocks.
The core. When the earths overall mass is compared to the density of rocks close to the surface it is indicated that the core must be greatly denser than the mantle, which itself is denser than the crust that surrounds it. studies have shown that the core is most likely to be made up predominantly from iron and nickle but roughly 8-12 percent is made up from another much lighter substance. This substance is thought to be sulphur. Another indication that there is a solid inner core is that some earthquake waves are not transmitted through the core directly and others are bent or refracted on the way through a zone known as the shadow zone. the inner core is thought to be only 5 percent of the entire core and surrounded in liquid. the earths magnetic field in nature seems to suggest that it is created by the swirling liquid of the outer core, rather like the swirling of the sea. The presence of a nickle iron alloy in the oldest of metiorites that were created around the same time and from that same materials as the earth also supports this theory.
The mantle. the mantle is made up mostly of fairly dense silicate materials. Some of these are in high pressure forms with close packed structures. Evidence of this comes from pieces of upper mantle material which are called xenoliths. The are brought to the surface very rarely by deep volcanism. these are usually composed mainly of peridotite. the lower mantle on the other hand is thought to be made up of much denser minerals similar to olivine but more compact such as perovskite. the very uppermost layers of the mantle are fused with the continental crust and together they form the lithosphere.