Which discontinuity marks the boundary between Earth’s crust and mantle?

The Mohorovičić discontinuity marks the boundary between Earth’s crust and mantle. It is commonly shortened to the Moho and was identified in 1909 by Croatian seismologist Andrija Mohorovičić.

Mohorovičić noticed that seismic waves from a Croatian earthquake arrived at some distant stations sooner than expected. He inferred that waves had travelled through a deeper, faster layer and refracted back toward the surface. The change reflects a jump in seismic-wave speed caused mainly by the transition from crustal rocks to denser mantle rocks.

The Moho is not at one universal depth. Beneath oceans it is often about 5–10 kilometres down, while beneath continents it commonly lies around 30–40 kilometres deep and can be much deeper under mountain belts. It is a compositional boundary, not the same thing as the lithosphere–asthenosphere boundary.

Scientists map the Moho using earthquakes, controlled seismic sources, and gravity data. Its depth helps reveal crustal structure and the effects of mountain building.