The lower mantle is much thicker than the upper mantle.

The base of the lower mantle is at about 2700 km.

This has been interpreted as their originating from a different region, suggested to be the lower mantle.

Some scientists believe this is a change in composition with little exchange of material between the upper and lower mantle.

He proposed that heat, but not material, is exchanged between the upper and lower mantle.

But if the conductivity inside the Earth were much higher than at the surface, then the Earth's core and lower mantle would also cool.

It is typical of melts that originated from the low mantle.

In his 1942 publication of his model, the entire lower mantle was the D layer.

Very little is known about the lower mantle apart from that it appears to be relatively seismically homogeneous.

There lava from the Earth's lower mantle or upper core is close to the surface.