The outer or upper zone of the Earth's core, extending from a depth of 2,900 km to 5,100 km, and including the transition zone; it is equivalent to the E layer and the F layer. It is inferred to be liquid because it does not transmit shear waves. Its density ranges from 9 to 11 g/cm₃. The outer core is the source of the principal geomagnetic field. Compare: inner core