Illustration showing the evolution of the interior of the planet Mars. At the start of the sequence (left) Mars has a silicate magma ocean (orange) and metallic core (yellow). The second panel shows the core has evolved into a solid inner core and a larger outer one, still liquid. Meanwhile, olivine from deep in the magma ocean drifts upwards due to buoyancy, and olivine from the shallows sinks, forming an olivine boundary and dividing the magma ocean in two. In the third panel, the both portions of the magma ocean have solidified. And in the final panel, there is partial melting of the upper mantle.