Field briefing: what lies beneath us?

Earth has four main layers. The crust is a thin, brittle skin of solid rock: it forms the continents and ocean floors and is broken into tectonic plates. Beneath it, the mantle is a thick layer of hot, mostly solid rock. Over long periods, parts of the mantle move very slowly, helping to move the plates above. The outer core is liquid iron and nickel; the movement of this electrically conducting metal helps generate Earth's magnetic field. At the centre, the inner core is solid iron and nickel. Although its temperature is extremely high, immense pressure keeps it solid. The crust and the uppermost mantle together form the rigid lithosphere.