Which layer of the Earth is the least dense?

The crust is the least dense layer of the Earth because it is composed primarily of lighter silicate rocks, such as granite and basalt. These materials have lower densities compared to those found in the deeper layers of the Earth. The crust floats on the denser underlying mantle, which is composed of heavier silicate materials.

In contrast, the inner core and outer core are made of denser materials, including iron and nickel, resulting in their higher density. The mantle, while also made up of silicate rocks, contains minerals that are denser than those found in the crust. This layering illustrates how density increases with depth into the Earth, making the crust the least dense of all the layers.