The rock goes through expansion-contraction cycles.
The inner core is very hot as is the rock surrounding it. As radioactive decay heats the rock it expands. The outer rock is still solid so it ends up with a lot of cracks that open up. This cause the rock to cool a bit. This cooling results in contraction.
The rock goes through expansion-contraction cycles.
The inner core is very hot as is the rock surrounding it. As radioactive decay heats the rock it expands. The outer rock is still solid so it ends up with a lot of cracks that open up. This cause the rock to cool a bit. This cooling results in contraction.