The flow of molten material in our planet’s outer core is the prime source of Earth’s magnetic field. That flow can fluctuate rapidly over large areas, recent data suggest, so geophysical models that estimate how the magnetic field evolves over time should account for such variations.
Earth’s outer core, a molten mix of iron and other metals
that is no more viscous than water, flows at an average speed of about 20
kilometers per year. Because that material contains charged particles, its flow
produces the planet’s magnetic field, says Nils Olsen, a geophysicist at the
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