Let's say that some aliens got mad at us and decided to destroy Earth. A young child on one of the alien starships was playing with his toy gun which could shoot normal bullets at relativistic speeds...

The bullet is a standard one, let's say for the sake of simplicity one that is used on a AK47. It is shot towards Earth at 0.99 c.

What would be the effects of the impact? I imagine the bullet doesn't have enough time to burn up in the atmosphere. Do the effects vary by impact angle?