Earth’s core consists mostly of iron. The outer core is hot enough for the iron to be liquid. The inner
core, although even hotter, is under so much pressure that it is solid. The mantle is made up of iron and magnesium silicate minerals. The bulk of the mantle, surrounding the outer core, is solid rock, but is plastic enough to be able to flow slowly. Surrounding that part of the mantle is a partially molten layer (the asthenosphere), and the outermost part of the mantle is rigid. The crust — composed mostly of granite on the continents and mostly of basalt beneath the oceans — is also rigid. The crust and outermost rigid mantle together make up the lithosphere. The lithosphere is divided into about 20 tectonic plates that move in different directions on Earth’s surface.
