What is the boundary called where Earth’s crust meets the mantle?

The boundary where Earth’s crust meets the mantle is called the Mohorovičić discontinuity, or Moho.

Croatian seismologist Andrija Mohorovičić identified this boundary in 1909 after studying earthquake waves. He noticed that some seismic waves arrived sooner than expected, suggesting they had traveled through a deeper layer where waves move faster. The Moho is therefore defined by a change in seismic-wave velocity, not by a visible surface exposed everywhere.

The Moho lies at different depths. Beneath oceanic crust it is generally only a few kilometres below the seafloor, while beneath continental crust it is commonly tens of kilometres down and can be deeper under major mountain ranges.

The Moho is often confused with other seismic boundaries. The Gutenberg discontinuity separates the mantle and outer core, while the Lehmann discontinuity is associated with the inner core boundary. Together, seismic-wave changes at these interfaces reveal Earth’s layered interior.