What is the primary composition of the lower mantle?

The primary composition of the lower mantle is best described as soft, slightly molten rock. This layer sits beneath the Earth's mantle and above the outer core, and is characterized by its semi-solid state due to extreme pressures and temperatures. Although there is heat sufficient to cause some melting, it does not create a fully liquid environment. The minerals in the lower mantle, primarily silicate minerals such as perovskite and post-perovskite, allow the material to behave like a viscous fluid over long periods, contributing to tectonic processes and the movement of the mantle as a whole.

In contrast, solid iron and nickel are more characteristic of the Earth's inner core, while liquid iron and nickel are found in the outer core. Crystalline silica, although present in the upper mantle and Earth's crust, does not characterize the chemical composition of the lower mantle to the same extent as silicate minerals do.