The charged currents in the outer conducting regions of the earth core are thought to be responsible for earth's magnetism. What might be the battery (ie the cource of energy ) to sustain these currents ?

Question

$\begin{array}{1 1} \text{electro magnetic radiation} \\ \text{radio active material} \\ \text{molter form of iron deposits} \\ \text{ All the above} \end{array} $