NASA's InSight probe has found that Mars' heart is totally liquid. This is unlike that of Earth, which combines a liquid outer core and a solid inner core.
The Martian core is not composed only or practically only of iron, but has high percentages of sulfur and oxygen, which are light elements. They have also found small amounts of carbon and hydrogen in the Martian core. Conditions inside a core play a key role in evolution, as do violent impacts on the surface of the planet.