The lithosphere, asthenosphere, inner core, and outer core areas of Earth are classified and divided into layers based on what?

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The lithosphere, asthenosphere, inner core, and outer core of Earth are classified and divided into layers based on density differences. 

Density is defined as mass per unit volume. Substances within a mixture will separate based on density differences. The substances with greater densities will sink while the substances with smaller densities will float. This phenomenon can be seen with a density column. 

Density increases as one travels from Earth's crust to its core. The densities of each layer of Earth are identified below. 

Crust = approximately 2.8 grams per centimeter cubed

Mantle = approximately 4.6 grams per centimeter cubed

Outer Core = approximately 10.5 grams per centimeter cubed

Inner Core = approximately 13 grams per centimeter cubed

Liquids are usually less dense than solids. The inner core is liquid magma while the crust is solid. However, the core does not reside on top of the crust. This is because the core is made of dense iron, nickel, and other heavy metals. The crust is made of lighter elements. The reason that the core is liquid is because of the force and weight caused by the layers above the core.  This pressure causes the core's materials to be under great pressure and temperatures, causing its materials to melt. 

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