What's in the center of the earth? The first thing to remember is that NOBODY has ever been there, so what you are about to hear is barely past the Wild and Crazy Idea stage. What we think we know comes from a study of how earthquake (seismic) waves travel through the earth, and how long it takes for them to get from where the earthquake happens to a recording station. The basic idea is that different materials transmit seismic waves at different speeds. With a lot of earthquakes and a lot of recording stations, geophysicists are beginning to get a pretty detailed picture of what is probably down there. One of the most distinctive features of the earth's interior is how it seems to be layered by density, with the heaviest stuff in the center, and the lightest material at the surface. In fact, the earth probably looks a lot like a hard boiled egg if you could cut it open. The yellow stuff in the center (the yolk) relates to what we call the core. Most geophysicists think that the core is composed of high density materials like iron and nickel. The egg's shell is like the earth's crust - a thin veneer of rigid, low density material at the surface. And all the white stuff in between is like the earth's mantle - the largest layer which, in the case of the earth, is of medium density, and, in the case of an egg, tastes best with a bit of salt and pepper.       Thanks to the Univ. of Oregon Tremors Student Earthquake Research  The core seems to be in two parts - a "solid" inner core with a "liquid" outer layer - and is the final resting place for as much of the high density material as can get there. The crust is REAL thin relative to the size of the earth - much, much thinner than an eggshell, and is of much lower density than the core. It is probable that the mantle represents the vast majority of the earth's mass which is still trying to figure out if it is heavy enough to be accepted at the core, or is lower in density and therefore has to float about on the surface with the rest of the scum.