Answer:
Moho
Step-by-step explanation:
The structure of the Earth is divided into layers. These layers are both physically and chemically different. The Earth has an outer solid layer called the crust, a highly viscous layer called the mantle, a liquid layer that is the outer part of the core, called the outer core, and a solid center called the inner core. The shape of the earth is an oblate spheroid, because it is slightly flattened at the poles and bulging at the equator. The boundaries between these layers were discovered by seismographs which showed the way vibrations bounced off the layers during earthquakes. Between the Earth's crust and the mantle is a boundary called the moho. It was the first discovery of a major change in the Earth's structure as one goes deeper. The moho, properly called the Mohorovičić discontinuity, is the boundary between the Earth's crust and the mantle. It was discovered by Croatian seismologist Andrija Mohorovičić in 1909. He discovered that seismograms of earthquakes showed two kinds of seismic waves. There is a shallow slower wave which arrives first, and a deep faster wave which arrives second. He reasoned that the deeper wave changed speed as it got just below the mantle. The reason it went faster was that the material of the mantle was different from that of the crust. The discontinuity lies 30–40 km below the surface of continents, and less deep below the ocean floors.[