Here's why:
* Core: The Earth's core is composed primarily of iron and nickel, which are extremely dense due to their atomic structure and the immense pressure at those depths.
* Mantle: The mantle is composed of silicate minerals, which are less dense than the core's metals. However, the mantle's density increases with depth due to the increasing pressure.
* Crust: The Earth's crust is composed of even lighter elements than the mantle, primarily oxygen, silicon, and aluminum. The crust has the lowest density of the three layers.
In summary: The deeper you go into the Earth, the denser the material becomes, with the core being the densest and the crust the least dense. This is primarily due to the composition of the layers and the increasing pressure at depth.
