Mohorovicic's observation, often referred to as Moho, was the detection of a boundary between the Earth's crust and mantle. In 1909, Mohorovicic noticed that seismic waves from earthquakes had differing velocities as they traveled through different layers of the Earth. He observed a marked increase in the velocity of seismic waves at a certain depth, indicating a boundary between the crust and mantle. This boundary, known as the Mohorovicic discontinuity or Moho, is now recognized as a significant distinction in Earth's structure.
