The Composition of the Mantle Is Thought to Be
The lower mantle below the transition zone is made up of relatively simple iron and magnesium silicate minerals which change gradually with depth to very dense forms. Going from mantle to core there is a marked decrease about 30 percent in earthquake wave velocity and a marked increase about 30 percent in density. Earthquake Illustrated Diagrams Earthquake Earthquake Magnitude Seismic Wave Traces of ancient life have been found in rocks deep inside the Earths mantle having been sucked down there hundreds of millions of years ago.