The Earth can be divided into one of two ways – mechanically or chemically. Mechanically – or rheologically, meaning the study of liquid states – it can be divided into the lithosphere, asthenosphere, mesospheric mantle, outer core, and the inner core. But chemically, which is the more popular of the two, it can be divided into the crust, the mantle (which can be subdivided into the upper and lower mantle), and the core – which can also be subdivided into the outer core, and inner core