James Dunlap age 11, of East Liverpool, Ohio, for his question:

How deep down is the earth's mantle?

We know that the solid materials of the earth get denser and denser, heavier and heavier, towards the center. The lightest materials are in the surface crust on which we live. The earths crust, which corresponds to a tissue thin peel on an orange, varies between 15 and 40 miles in thickness. Below the crust is a denser rocky layer reaching half way to the center of the earth. This layer surrounds the metallic core.

Some earth scientists refer to the layer between the crust and the core as the earth's mantle or the outer mantle. It begins below the crust 15 to 40 miles below our feet. Other experts call this layer the earth's dense rocky shell or the deep zone. They refer to the mantle as the shallow layer of soil and loose stones on the top of the crust.