What is the Mohorovičić discontinuity?

The Moho was identified in 1909 by Croatian seismologist Andrija Mohorovičić after he noticed earthquake waves arriving faster than expected. It marks the transition from the relatively light crust to the denser upper mantle. Under oceans, the crust is usually much thinner than under continents, so the depth of the Moho varies widely. Scientists study it using seismic waves because it cannot be seen directly except in rare exposed sections and deep drilling projects.