Objectives - Understand and model the new paradigm of soil carbon (C) stabilization at the C-microbe-mineral interface with varying: -Carbon input chemistry -Microbial community composition, and -Soil mineralogy - Integrate findings across spatial (molecular to landscape) and temporal scales using: Gradients of soil age (~40 to 250 ka), and climate (~300 to 1200 mm yr-1) - Incorporate improved mechanistic understanding of C stabilization/destabilization into new reactive transport models