Mohorovicic discovers the boundary between the crust and the mantle

After a strong earthquake near Zagreb on 8 October 1909, the Croatian seismologist Andrija Mohorovicic studied the records from many stations and noticed two sets of waves from the same shock: one that travelled directly and another that arrived earlier at distant stations. He concluded that the second set had been bent by a sharp change in the rocks at a depth of about 54 kilometres below the surface, where the speed of seismic waves increased. This boundary, now called the Mohorovicic discontinuity or Moho, separates the Earth's crust from the denser mantle. It lies at about 5 to 10 km under oceans and 30 to 70 km under continents.

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