Final answer:
The formation of Earth's magnetic field is explained by the geodynamic theory, which proposes that circulating liquid metallic elements in Earth's outer core create electric currents that generate the magnetic field.
Step-by-step explanation:
The currently accepted theory for the formation of Earth's magnetic field is the geodynamic theory. Essentially, this theory suggests that the magnetic field is generated by the movement of liquid metallic elements in Earth's outer core. This movement creates an electric current which, in turn, produces the magnetic field.
The geodynamic theory is supported by evidence such as the alignment of Earth's magnetic field with its rotational poles, the presence of a magnetosphere, and scientific experiments and modeling.
According to this theory, as the liquid metal circulates, a circulating electric current is set up, which produces a magnetic field. This circulating electric current is the result of the motion of charged particles. The movement of liquid metals in the outer core, driven by convection currents arising from the heat of the inner core, is what maintains the magnetic field. Sometimes, shifts in the flow can result in reversals of the magnetic field polarity, which can be observed in the geological record in rocks that have been magnetized during their formation.
The presence of Earth's magnetosphere extends the influence of the magnetic field beyond the planet, trapping charged particles from solar winds.