Scientists have mapped the boundary globally between the Earth's crust and its mantle - the so-called Moho boundary - in unprecedented detail.
They used gravity measurements from the European Space Agency's Goce satellite to model its location.
The famous "discontinuity" lies some 10-70km below the surface and marks a sharp change in rock properties.
It was first identified by the Croatian geophysicist Andrija Mohorovicic in 1909.
He determined the boundary's existence from the distinct behaviour of seismic waves produced by shallow earthquakes.