Polystrate fossils are a key indicator of this being true. Maybe not those overlapping one-or-two layers, but the fossilized trees that cut through many layers, as that logically sets the date of those layers to be the same (geologically speaking; before the tree can rot). Although I don’t know this to be true, I would not be surprised to find an unbroken chain of fossilized trues from the top of the geologic column right to the bottom, which would prove this idea writ large…