Low density of Earth's core due to oxygen and silicon impurities
During accretion and differentiation of the Earth, chemical interactions in a silicate magma ocean and liquid iron drove silicon and oxygen impurities into what went on to become the liquid outer core. Contrasting with previous research, which suggested that silicon and oxygen would only appear in very low concentrations (less than 1 percent by weight) in the liquid iron, Tsuno et al. find that at the base of a magma ocean 1,200 kilometers (750 miles) deep, these light elements could reach concentrations as high as 5 percent oxygen and 8 percent silicon by weight, simultaneously. Such impurity levels would decrease the density of the outer core, accounting for the so-called "density deficit" identified in previous research, whereby the outer core is roughly 10 percent less dense than a pure iron-nickel alloy.