1. Continental crust: This is the thicker, less dense crust that forms the continents. It's primarily composed of granitic rocks.
2. Oceanic crust: This is the thinner, denser crust that forms the ocean floor. It's mainly made of basalt and gabbro.
3. The uppermost mantle: This layer, often referred to as the lithosphere, is the rigid outermost layer of the Earth that includes both the crust and the uppermost part of the mantle.
So, while we often talk about the crust as a single layer, it's actually made up of two distinct types: continental and oceanic. And the lithosphere, which includes the crust and the uppermost mantle, is a crucial layer for understanding plate tectonics.