What is the state of earth's core? Solid? Liquid? How do we know?

The earth's core is sub-divided into a liquid outer core and a solid inner core. These states have been determined by the behavior of the shockwaves generated by earthquakes as they pass through (or don't pass through) the different mediums.

Thanks, Miles. Do you know how they can be in those two states when it's so hot there?

most materials take up less space in their solid form. at the center of the earth, there is a lot of pressure pushing in. basically, the pressure, which favors a solid core because it is more compact overwhelms the heat, which favors the freeer-moving liquid for (heat is just a measure of the movement of atomsandmolecules (well, technically their kinetic energy which is just a combination of their mass and their velocity)