What is the temperature and composition of the lowermost mantle?

The two large low-velocity provinces (LLVPs) are key features in the lowermost mantle, covering 25 % of
the core surface and rising 100s of km above the core-mantle boundary (CMB). Given their size, their
properties impact several planetary-scale processes including mantle convection, thermal evolution,
mixing of chemical heterogeneity, and ultimately plate tectonics. Their physical properties can also be
used to constrain possible hypotheses of their origin. LLVPs could be hot regions with concentrated
mantle plumes, or chemically distinct dense structures sculpted by mantle convection. Most existing
studies assume identical physical properties between the Pacific and African LLVPs, yet their differences
cannot be ignored (Garnero et al., 2016). Understanding the properties and origins of the two LLVPs is
thus important for resolving conflicting perspectives of the lowermost mantle between different scientific
fields. For example, the latter hypothesis provides a viable explanation to the disagreement of the Urey
ratio of 0.7 in geophysics and 0.3 in geochemistry (Labrosse et al., 2007)