Iron-Phosphorus Coupling and the Cambrian Threshold:A Three-Factor Co-Limitation Model for Complex Life

The Cambrian Explosion required simultaneous Fe, P, and O₂ availability — not oxygen alone. Schreibersite (Fe₃P) provides activated phosphorus with >10⁶ higher prebiotic phosphorylation yields than apatite, while the 4.5 Gyr delay reflects geochemical locks from magma ocean to Snowball Earth. Eukaryotic cells demand 10–100× more iron than prokaryotes, making Fe × P × O₂ co-limitation the true bottleneck for complex life.