The mantle is the Earth’s layer from the Moho discontinuity to the Gutenberg discontinuity at a depth of 2,900 km. The crust is above the mantle, and the core is below. The mantle is divided into the upper mantle and lower mantle by the Repetti secondary discontinuity. The upper mantle is mainly composed of magnesium-iron silicate rock with olivine, and the lower mantle mainly consists of magnesium-iron silicate rock with spinel and perovskite structures. The middle part of the upper mantle at depths of 60–400 km is a low-speed seismic belt (i.e., the asthenosphere). The lower mantle is in an uneven solid state and is mainly composed of a magnesium-iron silicate of perovskite. Compared with the crust, the iron and nickel contents are significantly higher, but the content of radioactive material is low.