 So the continental crust is made of granite, which as far as we know, is only abundant on our planet. We've never found it in a significant amount anywhere else that we've looked in the cosmos. And granite is less dense than basalt. So it will float on top of the basalt. And that's really where the continents came from in the first place, is that it was this less dense layer of granite that floated over the oceanic basalt and therefore rose above sea level over time.