I would not presume to have any opinion on the direction such traffic might have taken. All I know is the one certain, observed fact in this case is that pieces

I would not presume to have any opinion on the direction such traffic might have taken. All I know is the one certain, observed fact in this case is that pieces of Mars have indeed fallen to the surface of Earth. There is of course no known reason why the reverse would not have happened. From your writings (added to feed, thank you) I notice we share a belief: That life may well be quite common out there, but human level intelligence exceedingly rare. I somehow believed this from a very young age, long before I ever heard of Drake or his equation or any such calculation.