The division between the Earth's core, mantle, and crust is based on which criterion?

• A. The thickness of the layers.
• B. The density of the layers.
• C. The composition of those layers.
• D. The temperature of the layers.

Answer: (C)

Dividing Earth's interior into core, mantle, and crust is based on what each layer is made of. The crust is made of lighter silicate rocks, the mantle consists of denser magnesium- and iron-rich silicates, and the core is primarily metallic iron (with some nickel). This chemical makeup gives each layer distinct properties, like density and how seismic waves travel through it, which is why seismic studies reveal clear boundaries between them. Thickness, temperature, and even density vary with location and depth, but the defining criterion for these divisions is the composition of the materials.