What my own work did over a decade ago is predict the existence of an impact layer and that the related carbon content was actually comet dust. That comet dust is carbon is something else that is not presently understood but should have been inferred a long time ago in view of comet tail behavior.
The good news is that we now have a bevy of geologists gamely out looking and actually finding the noted layer using just this model.
Maybe in another decade they will catch on to the fact that it was all deliberate.
Comet Research Group responds to Robert Schoch