The thinner but more dense crust of the Earth is the oceanic crust.

Here's why:

* Thickness: Oceanic crust is typically 5-10 kilometers (3-6 miles) thick, whereas continental crust can be up to 70 kilometers (43 miles) thick.

* Density: Oceanic crust is primarily composed of basalt and gabbro, which are denser than the granite and other rocks that make up the continental crust.

This difference in density is why the oceanic crust sits lower than the continental crust, forming the ocean basins.