The layer of the Earth that has melted rock that moves like a thick liquid is the mantle.

Here's why:

* The mantle is a thick layer of mostly solid rock located between the Earth's crust and the core.

* The extreme pressure and heat within the mantle cause the rock to behave like a very viscous fluid over long periods of time.

* This slow movement of the mantle, known as convection, drives plate tectonics, which shapes the Earth's surface.

Let me know if you have any other questions!