The Earth's core occupies 17% of its volume and 33% of its mass. It consists of a solid inner core, also called the inner core, and a liquid outer core. The latter, composed of a liquid and conductive alloy of iron and nickel, is driven by turbulent convection movements due to the cooling of our planet. Fluid movements (in blue and red) stretch and twist the lines carrying the magnetic field (in orange). This is the dynamo effect, which, like a bicycle dynamo, ensures the conversion of mechanical energy into electromagnetic energy. In the case of the Earth, this process is called the "geodynamo".