Bruce DeVault, age l3, of Huntsville, Ala., for ha question:

What do they mean by the earth's mantle?

The word mantle means a cloak and a cloak usually is worn as an outside garment. You would expect the earth's mantle to be its outside layer of rocky minerals  but the outside skin of the earth is the crust. The mantle is the thick layer below the crust.

The average thickness of the crust is about 20 miles. Its layers of light rock rest upon the mantle which reaches down to a depth of l,800 miles. As we go deeper, the pressure and temperature increase, and 200 or 300 miles down it is as hot as an oven. The bottom of the mantle rests on the outer core and the outer core surrounds a dense ball called the inner core.