Suspected in the form of Ice comets, yes. It arrived. there are many other theories, though.
SUSPECTED, and are many THEORIES. Which means, IF this happens, then this POSSIBLY happend which MAY have lead to this.
This is the main reason I don't believe science, it's very much circumstantial when it comes to this stuff.
Created by a giant man in the sky? This is sound logic to you?
At least I have an explanation that isn't circumstantial.