P Waves:
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S Waves:
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During the 20th century, studies of the paths of P and S waves through the Earths layers helped scientists identify the boundaries of Earths layers and determine that the outer core is liquid. They found that the velocity of seismic waves increased abruptly about 50 km below eastern Europe, named the Moho discontinuity. It was also observed that P waves bent around the outer core and the inner core slow them down this area is called the shadow-some.