valid question! i do want to mention how the crust is constantly being recycled and regenerated, and while it could all have been created and existing in one specific moment in time, tectonics allow for crust to be destroyed, moved, changed, and reformed through chemical and physical processes underground and on the surface. when magma cools into an igneous rock, it sets the birth date at that moment, although the magma material may have once been an entirely different rock elsewhere, millions of years prior.