Field notes

Earth is made of four main layers. The thin, solid crust is the rocky surface where we live. Beneath it is the mantle, a very thick layer of hot rock that is mostly solid but can slowly flow over long periods. The outer core is a liquid layer made mostly of iron and nickel. At the centre is the inner core, a solid ball made mostly of iron and nickel. Despite its extreme heat, immense pressure keeps the inner core solid. Temperatures generally increase towards Earth’s centre. The crust is the thinnest layer; the mantle is the thickest.