[WheelsAtLarge]

I think it speaks to the fact that there are some many people in the world. If you fire a bullet towards the sky in a major city, I bet, there's a good chance that it will hit someone on its way down. It's definitely above 0. It's the same with meteorites.

[eesmith]

https://en.wikipedia.org/wiki/Celebratory_gunfire confirms it's non-zero.