The Earth's mantle is a complex layer that's not typically divided into three distinct parts. It's more accurately described as having two main sections:

1. Upper Mantle: This is the section closest to the Earth's surface. It's further subdivided into:

* Lithosphere: The rigid outer layer of the Earth that includes the crust and the uppermost part of the mantle.

* Asthenosphere: A semi-solid, ductile layer located below the lithosphere. It's where convection currents occur, driving plate tectonics.

2. Lower Mantle: This is the deeper, hotter, and denser part of the mantle. It's mostly solid but can deform over very long timescales.

So, while there are three distinct components within the upper mantle, the Earth's mantle as a whole is generally divided into upper and lower sections.