The mantle lies tens of kilometers to about 2900 kilometers below the earth's crust and surrounds the earth's inner core  According to the different propagation speeds of seismic waves in the earth's interior, the mantle is considered to be divided into upper and lower layers 660 kilometers underground  The upper mantle is composed of minerals with high magnesium content such as olivine, while the composition of the lower mantle is not clear  In the past, researchers believed that, Due to the internal convection movement about 4 billion years after the birth of the earth, the mantle has been homogenized, and the minerals constituting the upper mantle and the lower mantle should be the same
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 increase, and the material is solid
 However, recent studies have found that the minerals constituting the upper and lower mantle are different