* Continental crust: Typically ranges in thickness from 30 to 70 kilometers (19 to 43 miles). It is composed primarily of granitic rocks, which are rich in silica and aluminum.

* Oceanic crust: Typically ranges in thickness from 5 to 10 kilometers (3 to 6 miles). It is primarily composed of basalt and gabbro, which are denser and richer in magnesium and iron than granite.

Here's why this difference exists:

* Formation: Continental crust forms through a process called plate tectonics, where tectonic plates collide and fold, creating mountains and landmasses. This process involves the melting and re-melting of rocks, resulting in the formation of granite-rich continental crust. Oceanic crust forms at mid-ocean ridges where magma rises and cools, creating basalt and gabbro.

* Density: Continental crust is less dense than oceanic crust. This is because it is rich in lighter elements like silica and aluminum. This lower density allows continental crust to "float" higher on the mantle, making it thicker.

* Age: Continental crust is generally older than oceanic crust. This is because oceanic crust is constantly being recycled at subduction zones, where it sinks back into the mantle. Continental crust, on the other hand, is more resistant to subduction.

In summary, the differences in composition, density, and age contribute to the thicker nature of continental crust compared to oceanic crust.