Within the Earth, this relationship is determined primarily using seismic waves, as their velocity is dependent on density, complemented by gravitational-field and free-oscillation measurements. The upper mantle is complicated by the presence of phase transitions, particularly at depths of around 300 km and 650 km. Within the lower mantle, the density increase with depth is essentially adiabatic, except in the region immediately overlying the core. The outer core density (about 10 000 kg/m3) is almost twice that of the lower mantle (about 5000 kg/m3), reflecting a compositional change. The core density increases with depth, with a small jump from the outer to inner core of 12 000 kg/m3 to 13 000 kg/m3.
Subjects: Earth Sciences and Geography.