The "D layer," also known as the D" layer, is a region located at the bottom of the Earth's mantle, just above the outer core. It is characterized by its unique properties, including variations in temperature and composition. This layer plays a crucial role in the dynamics of the Earth's interior, influencing tectonic activity and the movement of tectonic plates. The D layer is approximately 200 kilometers thick and is composed of partially molten rock and minerals. Its behavior affects the flow of material between the mantle and the outer core, contributing to the generation of the Earth's magnetic field. Understanding the D layer helps scientists learn more about the planet's geological processes.