Sediments at the top of Earth's core

Unusual physical properties at the core-mantle boundary have been inferred from seismic and geodetic observations in recent years. We show how both ty pes of observations can be explained by a Layer of silicate sediments, whic h accumulate at the top of the core as Earth cools. Compaction of the sedim ents expels most of the Liquid iron but Leaves behind a small amount of cor e material, which is entrained in mantle convection and may account for the isotopic signatures of core material in some hot spot plumes. Extraction o f Light elements from the Liquid core also enhances the vigor of convection in the core and may increase the power available to the geodynamo.