The Earth's crust is less dense than the mantle, which lies beneath it.

Here's why:

* Composition: The crust is primarily composed of lighter elements like silicon, oxygen, aluminum, and iron. The mantle, on the other hand, contains denser materials like magnesium and iron.

* Density Comparison: The average density of the crust is around 2.7 g/cm³, while the mantle's density is around 3.3 g/cm³.

* Continental vs. Oceanic Crust: The continental crust is thicker and less dense than the oceanic crust. This is why continents "float" higher than the ocean basins.

This difference in density is crucial to understanding plate tectonics and the movement of the Earth's crust.