The internal structure of the Earth is made up of the asthenosphere, the upper mantle, the lower mantle, the outer core and the inner core. These structures support the crust of the Earth.
The asthenosphere is a semisolid layer of hot rock that's found at the top of the upper mantle. It is thinner beneath the oceanic crust and thicker beneath the terrestrial crust. The transition between the crust and the upper mantle is known as the Mohorovi?i? discontinuity, or the Moho.
The mantle proper makes up most of the Earth's internal structure. The upper mantle is about 410 miles thick. Earthquakes don't originate deeper than this.
Another discontinuity separates the upper mantle from the lower mantle, which then extends down to 1678 miles to the outer core. At these depths, the pressures and heat change the nature of the rocks. There are also a couple of discontinuities, including the mysterious D double prime. There, the rocks are subject to pressures of as much as 20 million pounds per square inch.
The core of the Earth is in its center. The outer core is liquid, a little over 1300 miles in diameter and made of an alloy of nickel and iron. The inner core is about 760 miles in diameter and is made of solid iron.