The Earth's mantle is a single, thick layer between the crust and the core. It's often divided into:
* Upper Mantle: This is the layer closest to the crust. It includes the lithosphere, a rigid layer made of the crust and the uppermost part of the mantle, and the asthenosphere, a partially molten, more ductile layer.
* Lower Mantle: This is the denser, more rigid layer below the asthenosphere.
While the lithosphere and asthenosphere are important parts of the upper mantle, they are not considered "spheres" in the same way the Earth's crust, mantle, and core are.
It's possible you're thinking of the hydrosphere (water), atmosphere (air), and biosphere (life) which are the three main spheres of the Earth system.
