Here's why:
* Density: The inner core is composed primarily of iron with a small amount of nickel. It's incredibly dense, with estimates ranging from 12.6 to 13.0 g/cm³. This is due to the immense pressure from all the layers above it.
* Temperature: The inner core is incredibly hot, with temperatures estimated to be between 5,200°C (9,392°F) and 6,000°C (10,832°F). This heat is generated from the decay of radioactive elements within the Earth and the residual heat from the planet's formation.
While the outer core is also incredibly hot, it's less dense because it's in a liquid state. The inner core's immense pressure forces the iron and nickel into a solid state, despite the extreme temperatures.
