https://www.youtube.com/watch?v=qxPyREGLAtc
Seismic tomography maps two continent-sized piles of anomalous rock at Earth’s core–mantle boundary — Large Low-Shear-Velocity Provinces (LLSVPs) beneath Africa and the Pacific.
One line of research argues these dense mantle reservoirs could be leftover Theia material from the giant impact that formed the Moon, consistent with their size, age indicators, and density contrasts in convection models.