Crust is the outermost layer of Earth. The crust is solid and relatively thin, and it lies below both landmasses and oceans. The dry land of Earth’s surface is called the continental crust. It is about 15 to 75 km (9 to 47 mi) thick. The oceanic crust is thinner than the continental crust. Its average thickness is 5 to 10 km (3 to 6 mi). The crust is very thin in relation to the rest of Earth.
If a trip to the center of Earth at 100 km/h (60 mph) were possible, it would take 64 hours, of which only the first 15 to 45 minutes would be in the crust. The crust has a definite boundary. This boundary, called the Mohorovicic discontinuity, or simply the Moho, after the Croatian geologist Andrija Mohorovicic, separates the crust from the underlying mantle. Mohorovicic discovered the boundary in 1909, when he observed that earthquake waves do not pass through Earth’s interior in a straight line but change course at a certain depth below the surface. He believed that the point at which these waves change course marked the boundary between the crust and the mantle.