Seismic mapping of North America has revealed that an ancient slab of crust buried beneath the Midwest is causing the crust ...

Although this inner core is white hot, the pressure is so high the ... thick and appears to be divided into two layers: the upper mantle and the lower mantle. The boundary between the two lies ...

The potential compositional boundary was typically put at 660 km depth, corresponding to the major seismic discontinuity that marks the boundary between the upper mantle and lower mantle.