The mantle is located at a depth of tens of kilometers to about 2900 kilometers below the crust, enclosing the core of the earth's interior. According to the different speeds of seismic wave propagation inside the earth, the mantle is considered to be divided into upper and lower layers at 660 kilometers underground, and the upper mantle is composed of olivine, etc. The composition of minerals with high magnesium content and the composition of the lower mantle is not clear. In the past, researchers believed that the mantle had been homogenized due to the internal convective movement of about 4 billion years after the birth of the earth, forming the minerals of the upper and lower mantles. The matter should be the same, but recent studies have found that the minerals that make up the upper and lower layers of the mantle are different. To reach the above conclusions, the arguments that need to be supplemented most are:. ['The propagation speed of seismic waves is different in different minerals. Based on this, the propagation speed of the seismic waves in the upper and lower mantles is different.', 'Experiments have shown that the mantle has been continuously convective since the birth of the earth, but the speed of convection will continue to change as the internal temperature changes.', 'c. Previous research suggested that the composition of the mantle was affected by the impact of meteorites more than 4 billion years ago, but it was later found that the composition of the mantle is consistent with the average composition of other planets in the solar system, and the impact of the meteorites did not cause significant changes.', 'According to research, the upper mantle is likely to be the birthplace of magma, and the material is liquid, but the temperature, pressure, and density of the lower mantle have increased, and the material has a wing-shaped solid state.']