Blobs of crust that excite

11 May 2010 May 9th ... old pieces of continental crust that are thought to fall to the bottom of earth's mantle region are being blamed for mysterious dents in the planet's gravitational field. At some points on  the globe, such as the middle of the Indian Ocean, the NE Pacific, and the Ross Sea, earth's gravitational field is weaker. Scientists have suggested slabs of crust swallowed by the mantle following the collision of continental plates are at fault. As the slabs descend they force plumes of less dense material to rise and the distribution of the weak spots, it is claimed, reflect the pattern of the plumes. Naturally, other scientists disagree.