Seismic waves generated by earthquakes travel through Earth’s solid iron inner core faster in the direction of the rotation axis than along the equator. Scientists created a core growth model to explain this. To fit seismic data, the model predicts that asymmetric growth of the core leads to crystal movement that preferentially aligns iron-nickel crystals north-south. The model implies that the core is only 0.5-1.5 billion years old, a fraction of Earth’s age.
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Source: ScienceDaily