MANTLE

The mantle
Underlying the crust is the mantle, which is composed mainly of minerals containing magnesium, iron, silicon, and oxygen. The uppermost section of the mantle is a rigid layer. Combined with the overlying solid crust, this section is called the lithosphere, which is derived from the Greek word lithos, meaning "stone."

At the base of the lithosphere, a depth of about 40 miles (65 kilometers), there is another distinct seismic transition called the Gutenberg low velocity zone. At this level, all seismic waves appear to be absorbed more strongly than elsewhere within Earth. Scientists interpret this to mean that the layer below the lithosphere is a zone of partially melted material. This "soft" zone is called the asthenosphere, from the Greek word asthenes, meaning "weak." It extends to a depth of about 155 miles (250 kilometers).

This transition zone between the lithosphere and the asthenosphere is named after American geologist Beno Gutenberg (1889–1960).