Scientists believe the Earth's inner core is most likely made of solid metals.

Here's why:

* Extreme pressure: The immense pressure at the Earth's core, estimated to be over 3.5 million times the pressure at sea level, forces the iron and nickel to solidify, despite the extreme temperatures.

* Seismic waves: The way seismic waves travel through the Earth provides evidence of a solid inner core. These waves travel faster through solid materials.

* Earth's magnetic field: The Earth's magnetic field is thought to be generated by the movement of molten iron in the outer core, which is surrounding the solid inner core.

While the inner core is thought to be mostly solid, it's not completely rigid. It's more like a very dense, hot, solid that can still deform under immense pressure.