The energy released by these impacts left most, perhaps all, of the planet molten, whereupon the rocky magma separated from the molten iron. Some elements are more soluble in iron than in magma. These are called 'siderophiles', meaning iron-loving, and they are thought to have segregated to the Earth's core when the world was a young fiery ball. Because of this, the mantle is low in siderophile elements. This becomes clear if we compare the chemical composition of the mantle with those of a certain kind of meteorite called chondrites.
Chondrites are almost as old as the Earth.
They are thought to be left-over lumps of the planetesimals from which the planets formed. Some siderophile elements, such as vanadium and chromium, are more abundant in chondrites than in the Earth's mantle, suggesting that they must indeed have flocked to the iron core. But other iron-lovers, such as calcium and scandium, are surprisingly abundant in the mantle, they are known to dissolve better in molten silicate than in iron. These odd elements are said to be 'refractory' lithophiles. And then there is niobium.