First of all, the Earth shows it's magnetic field because of it's internal geodynamic nature. And it is believed that Earth's outer core is responsible for this kind of behavior. Unlike the mineral-rich crust and mantle, the core is made almost entirely of metals. Along with iron (Fe), silicon (Si) is also found at Earth’s
core whose thermal conductivity has an impact on Earth’s thermal structure,
evolution, and dynamics, as it controls the magnitude of thermal and
compositional sources required to sustain the internal geodynamo of Earth. Scientists
have directly measured the thermal conductivity of both solid Fe and Fe-Si
alloys up to 144 GPa and 3300 K. 15 at% Si alloyed in Fe significantly reduces
its conductivity by almost 2 folds at 132GPa and 3000 K. At similar
pressure-temperature conditions, an outer core with 15 at% Si would have a
conductivity of about 20 W m-1 K-1, which is lower than
pure Fe. This suggests that a lower minimum heat flow, around 3TW, across the
core-mantle boundary than previously expected, and thus less thermal energy
needed to operate the geodynamo.
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