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Magnetism and Matter
Question
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Answer the following question:
The earth's core is known to contain iron. Yet geologists do not regard this as a source of the earth's magnetism. Why?

Answer

Earth's core contains molten iron (which is the phase of the iron at the high temperatures of the core) which, is not ferromagnetic due to temperature beyond Curie temp. 

Note: Ferromagnetic subtances are those which gets strongly magnetised when placed in external magnetic field.

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Geologists claim that besides the main magnetic N-S poles, there are several local poles on the earth's surface oriented in different directions. How is such a thing possible at all?

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The earth's magnetic field varies from point to point in space. Does it also change with time? If so, on what time scale does it change appreciably?

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The earth's core is known to contain iron. Yet geologists do not regard this as a source of the earth's magnetism. Why?

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The charged currents in the outer conducting regions of the earth's core are thought to be responsible for earth's magnetism. What might be the ‘battery’ (i.e., the source of energy) to sustain these currents?

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The earth may have even reversed the direction of its field several times during its history of 4 to 5 billion years. How can geologists know about the earth's field in such distant past?