<b>Reassessing the Foundations of U–Pb Zircon Dating:</b><b> A Physical Model Replacement for Ionic Assumptions</b>

This brief challenges the foundational assumptions of U–Pb zircon geochronology. It demonstrates that lead is not chemically excluded by zircon during crystallization, as commonly believed, but is instead physically purged from the system before crystallization occurs. This shifts the start time of the decay clock and undermines the premise that zircon U–Pb dating reflects absolute formation ages. A thermodynamically grounded model is proposed, treating radiometric ages as conditional time markers rather than absolute chronometers.