The layer of the Earth that is solid due to tremendous pressure is the inner core.

Here's why:

* Composition: The inner core is primarily made of iron with a small amount of nickel.

* Pressure: The immense pressure from the weight of all the layers above it is so great that it forces the iron atoms to pack tightly together, making the inner core a solid despite its incredibly high temperature (around 5,200° Celsius).

Let me know if you have any other questions!