The Earth’s outer core is the second innermost layer, located between the inner core and the mantle. It contains mostly iron and nickel, which- due to lower pressure than existing at the inner core- are in the liquid form.
Temperature, composition and pressure differences that occur withing the outer core cause convective motion of the fluid. In addition, the Coriolis force acting on the fluid organizes this motion into rolls aligned with the Earth’s spin axis. Electric current is generated inside each roll, which is the source of its magnetic field. As these magnetic fields act in the same direction, their effect adds up to create the overall geomagnetic field that extends far into space and protects the atmosphere of our planet against solar wind.