That's a cool thought. I always imagined it be something like a the K-T boundary (1), a thin layer of rock that looks different than all of the other layers. (

That's a cool thought. I always imagined it be something like a the K-T boundary (1), a thin layer of rock that looks different than all of the other layers. (1) https://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_boundary https://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_b...