What is the temperature and composition of the lowermost mantle?

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The two large low-velocity provinces (LLVPs) are key features in the lowermost mantle, covering 25 % ofthe core surface and rising 100s of km above the core-mantle boundary (CMB). Given their size, theirproperties impact several planetary-scale processes including mantle convection, thermal evolution,mixing of chemical heterogeneity, and ultimately plate tectonics. Their physical properties can also beused to constrain possible hypotheses of their origin. LLVPs could be hot regions with concentratedmantle plumes, or chemically distinct dense structures sculpted by mantle convection. Most existingstudies assume identical physical properties between the Pacific and African LLVPs, yet their differencescannot be ignored (Garnero et al., 2016). Understanding the properties and origins of the two LLVPs isthus important for resolving conflicting perspectives of the lowermost mantle between different scientificfields. For example, the latter hypothesis provides a viable explanation to the disagreement of the Ureyratio of 0.7 in geophysics and 0.3 in geochemistry (Labrosse et al., 2007)