Because the outercore applies pressure to the innercore. Its like the book stack effect, pile up 5 books. Which book has the most pressure on it? The bottom. Now imagine that being a CIRCLE of books, the INNERbook or the innercore would have the most pressure.
Solid
I know it is nickel
crust mantle outtercore innercore
hot burning rock and magma
lithosphere asthenospere mesosphere outercore innercore
Around 5,400 degrees Celsius to 6,000 degrees Celsius.
Heavy (or dense) ones ...mostly iron.
inner core
The centre of the Earth's core - is a solid iron sphere.
The primary source of heat energy driving plate tectonics on Earth is radioactive decay in the planet's interior. This process generates heat through the decay of radioactive elements within the Earth's core and mantle, resulting in convection currents that drive the movement of the planetary plates.
The Wikipedia article on "Earth" mentions that at the center, the temperature "may" be up to 6000 degrees Celsius.
The radius of Earth's inner core is roughly 1,220km (658miles), made of mostly (about 80%) solid iorn.