* Upper mantle: This layer extends from the base of the crust down to about 660 kilometers (410 miles). It is composed primarily of peridotite and is divided into the lithosphere (rigid) and asthenosphere (partially molten).
* Lower mantle: This layer extends from the base of the upper mantle to the top of the Earth's core at a depth of about 2,890 kilometers (1,795 miles). It is composed of silicate minerals that are denser and hotter than those in the upper mantle.
Therefore, there is no distinct "middle mantle" layer. However, some geophysicists use the term "transition zone" to refer to the boundary between the upper and lower mantle, which lies at a depth of around 410-660 kilometers. This region is characterized by significant changes in mineral phases and physical properties.
It's possible that the term "middle mantle" is being used in a specific context, such as a research paper or educational material. If you have a specific source or definition for "middle mantle," please provide it, and I can give you a more precise answer.
