Earth's hot middle layer is known as the mantle. Earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth). The mantle is composed of silicate rocks and has a thickness of about 1800 miles (or 2900 kilometers). The material in the layer is solid, but behaves like a plastic (i.e. like very viscous fluid). It is this property of the mantle that allows motion of tectonic plates (the fragments of Earth's crust), resulting in earthquakes, volcanic eruptions and formation of land mass. Rocks in Earth's mantle experience temperatures of up to 4000 degrees Celsius (near the Core), but stay solid due to enormous pressure.
Hope this helps.