Iron, Silicon, and Planetary-Biological Coupling Geometry: The d-Cascade Bridge from Nuclear Binding to Human Thermoregulation

Demonstrates a continuous coupling geometry connecting nuclear binding energetics to human thermoregulation. Earth's Fe/Si compositional mass ratio (1.988) sits 0.068 from convergence invariant alpha=1.920. NHANES 2017-2018 analysis reveals median human lean-to-fat ratio of 1.928 — within 0.008 of the invariant. Iron deficiency collapses tissue coupling dimensionality (d*=9.5 vs 14.4; p<10^-6). Fe/Si and lean/fat ratios approach 1.920 on the same slope with d* ratio 1.065. Establishes nuclear physics as fifth GCT validation domain.