How is the structure of Earth's layers primarily defined?

The structure of Earth's layers is primarily defined by their density and composition. Each layer of the Earth—namely the crust, mantle, outer core, and inner core—differs in both material make-up and physical properties.

For instance, the crust is made up mainly of lighter, silicate minerals, which gives it a relatively low density compared to the underlying mantle, which consists of denser silicate materials. The outer core, made of molten iron and nickel, has an even higher density, while the inner core, although solid, is composed of the densest materials found within the Earth.

This layering is a result of the processes involved in planetary formation and the differentiation of materials based on their densities. Denser materials tend to sink towards the center, which is why we see a heavier composition in the inner core compared to the outer layers. Understanding these layers in terms of their density and composition helps geologists and scientists explore Earth's formation, structure, and dynamics.