* Two Types of Crust: The crust is actually divided into two distinct parts:
* Oceanic Crust: This is thinner, denser, and mostly composed of basalt. It averages about 5-10 kilometers thick.
* Continental Crust: This is thicker, less dense, and mostly composed of granite. It averages about 30-70 kilometers thick, but can be much thicker in mountainous areas.
* Variable Thickness: Even within each type of crust, the thickness can vary significantly. Mountains, for example, represent areas where the continental crust is thicker.
* Density: The density of the crust also varies, but generally ranges from 2.7 to 3.0 grams per cubic centimeter (g/cm³) for continental crust and 2.9 to 3.0 g/cm³ for oceanic crust.
Therefore, it's more accurate to talk about the density and thickness of specific parts of the crust, rather than providing a single value for the entire "first layer."
