Assertion: hot spot | /r/HasProperty | either a shallow interface
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Source sentences:
text: Geophysicists believe that hotspots originate at one of two major boundaries deep in the Earth, either a shallow interface in the lower mantle between an upper mantle convecting layer and a lower non-convecting layer, or a deeper D'' ("D double-prime") layer, approximately 200 kilometres (120 mi) thick and immediately above the core-mantle boundary.