Lost continents and preserved primordial reservoirs: A history both ancient and deep

            The Earth's deep interior is a dynamic environment that convects and stirs on billion-year timescales. Plate tectonics injects depleted mantle lithosphere, continental crust, and altered oceanic crust into the mantle, thereby permitting communication between surface and deep reservoirs in the Earth over geologic time. While the fate of subducted material is not known, it constitutes a significant reservoir in the Earth's mantle that may be sampled by buoyantly upwelling mantle plumes that source volcanic hotspots. We identify geochemical signatures in plume-fed volcanic hotspots that are consistent with an origin by recycling of oceanic and continental lithosphere that was processed in ancient subduction zones. Critically, we find evidence that the concentration of enriched mantle (EM) domains in southern hemisphere hotspots is the result of the late Neoproterozoic transition to deep slab breakoff — which permitted subduction of continental crust to mantle depths for the first time — when the continents were located in the southern hemisphere as Gondwana assembled. Additionally, we have identified fingerprints of surviving relics of Earth's earliest history in lavas with primordial noble gas signatures. Mantle domains sampled by these lavas date to the earliest Hadean, prior to the formation of the moon, and provide insights into the earliest evolution of the planet. The location of this primordial domain in the Earth's deep interior is not known, but constraints from geophysical and geochemical datasets provide important clues.