Discontinuities are changes that seismic waves present in their trajectory and speed because the properties of the medium they pass through become different. That is what has allowed geologists and geophysicists to know the internal structure of the planet and deduce its composition.
Specifically, the discontinuity represented by the end of the crust and the passage to the upper mantle is the Mohorovicic discontinuity, or as it is briefly called the Moho.
The depth at which it is found varies greatly because the thickness of the crust is very different depending on whether it is oceanic crust (about 7 km) or continental crust (up to 100 km under the great mountain ranges).
