Significant developments in crust mining operations, large-scale engineering projects, and energy processing allowed the people to reach deeper and deeper into their planet for resources. After all, the laws of physics indicate that the deeper you reach the heavier elements you can find, and the laws of the economics say that the heavier (thus rarer) an element is, the more money it is worth. Mantle Engineering is the new radical step in that direction, where engineers developed means to extract minerals from under Earth's crust layer directly via "thermal boreholes", or ultra-deep shafts protected by forcefields. This magma is filtered through a number of facilities that separate rare particles from molten rock, and the residue is returned to the mantle before extracting the next "pulse" of magma. While not very friendly to the environment, boreholes became crucial to the economy of most political powers of the era.