I think I remember reading once that all, or most of the gold on and in earth came from asteroids. If so, wow, that is a lot of asteroid contact in the past, but when would it have happened? We go from earth created, man created, to modern time with no record of massive asteroid impacts the world over- there have been some of course, but the amount of gold is staggering.
Gold, and all other heavy metals, is created in the heart of stars when they go supernova and their debris contents are spread over vast stellar distances.
Some aggregate and form asteroids, some form new stars and planets................