Also keep in mind that if you have a question it is likely that others in the class have similar ones, so don't think of questions as disruptive. These can be subdivided into the Lithosphere - the rigid oceanic and continental crust along with some entrained mantle that has cooled and stuck to the bottom. Asthenosphere - the partially molten upper mantle. Mesosphere - pressure is great enough in the lower mantle that the mesosphere is rigid, despite the intense temperature. Outer Core - The core of the planet is composed largely of nickel and iron, two very dense metals.
Temperatures are high enough that the outer core is molten.
Inner Core - Pressure at the inner core is great enough that the inner core, like the lower mantle, is solid. Remarkably, the inner core spins at a velocity that is greater than that of the earth as a whole due to its greater angular momentum. This story is starting to make its way from the pages of research journals into the popular literature. Consider the following web article. Columbia University scientists described the situation as being virtually a planet within a planet.