Internally, the deeper within the Earth you go, the hotter it gets. This is because of the internal temperature given off by the Earths core, which is transferred throughout the mantle via convection cells. The part of the mantle you are asking about, the asthenosphere, occurs around the 50 to 60 mile depth mark underneath the lithosphere, which is the solidmost, outer part of the Earth. At this depth the temperature ranges from 650 degrees Celsius to 1200 degrees Celsius. This is an equivalent Fahrenheit temperature of 1202 to 2192 degrees. At his temperature, rock should be able to melt, but due to the increased pressure from all the overlying layers of rock, the magma material undergoes a quality called plasticity. It is this quality of plasticity that allows the lithospheric plates on Earths surface to shift and undergo tectonic plate movement. This plate movement influences earthquake and volcanic activity on the surface of the Earth.