• inner core: solid, dense, Fe-rich
• outer core: liquid, dense, Fe-rich
• mantle: solid, (Mg, Fe)SiO₃ [Olivine-Peridotite-Spinel]
• Asthenosphere: partially molten portion of upper Mantle
• Crust: oceanic (sima) vs. continental (sial)

B. Earth structure is determined by studying the behavior of P and S waves generated by earthquakes and looking at variation in seismic wave velocity. Changes in mantle are due to increasing pressure which causes changes in atomic packing to increase density without alterning chemical composition.

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