The Earth's Continents
We all know that the land masses on Earth include seven continents. The continents rest on the Earth's crust, indeed they are part of the crust of the Earth.
Continental crust can be as thick as 30 km or so, oceanic crust is typically 15 km. Continental crust is both higher in elevation than oceanic crust, and deeper in depth than oceanic crust. This means that for every mountain range reaching into the sky, there is an equally deep "root" with reaches down into the depths of the interior of the Earth. The height and depth of this portion of crust, as well as some of its chemical properties, is what differentiates continental crust and oceanic crust.
The interface between the crust and the underlying lithosphere is called the Mohorovisic Discontinuity, or moho, and can range in depth from 10 km to 30 km. The moho is mapped using sonic techniques.