The layer of the Earth where rock melts and forms magma is called the mantle.

Here's why:

* The mantle is a layer beneath the Earth's crust. It's primarily made up of solid rock, but the intense pressure and heat from the Earth's core cause some of the rock to partially melt.

* Magma is molten rock found beneath the Earth's surface. It forms within the mantle, and can sometimes rise up through the crust, leading to volcanic eruptions.

Let me know if you have any other questions about the rock cycle!