They compared the mapped location of the ULVZ with the known position of mantle hot spots.
The researchers report finding strong evidence linking the ULVZ to the position of hot spots.
He says that researchers will need to survey the rest of the globe to see just how pervasive the ULVZ is.
If the link between hot spots and the ULVZ holds, it offers insight into aspects of Earth's evolution.
Following that nomenclature, then, the ULVZ may be the dregs of the mantle--in other words, the densest rocks in the planet.
Or the ULVZ may contain iron-rich minerals, created when mantle minerals react with the molten iron of the outer core.