The key characteristics of the Earth's layers are the thinness of the crust, the rigidity of the upper mantle and the viscosity of the lower mantle and the asthenosphere. Other characteristics are the liquid state of the outer core, and the great heat and pressure of the inner core.
Most of the surface of the Earth is made up of water, which comprises the oceans. However, the crust of the earth, which lies beneath the oceans and floats the continental plates, is solid and made largely of basalt and granite. The crust under the oceans is between 3.7 and 6.8 miles thick, while the crust that makes up the continents is between 15.5 and 56 miles thick
The upper mantle is separated from the crust by the Mohorovicic discontinuity. It is rigid and between 62 and 124 miles thick. The asthenosphere, a flowing layer, is part of it. Beneath it is the lower mantle. All in all, the mantle is about 1800 miles deep and gets hotter as it gets deeper. The lower mantle has temperatures of about 4000 degrees Fahrenheit. The heat within the mantle circulates in convection currents.
The outer core of the Earth, separated by the Gutenberg discontinuity, is made up of liquid nickel and iron and is 1400 miles deep. The inner core is solid, even though the temperature is 9000 degrees F. This is because the pressure there is 45,000,000 pounds per square inch.