as much as alot of people want to rid this planet of their own species, i really do not see it happening anytime soon... i mean hell, to even wipe out 50% of the people int he world you'd need some sort of super virus that can be passed along by touch, air, blood, everything, and can live outside of a host for probably atleast days... either that or a meteor... 3 billion people is alot of people to kill... it would take something massively devestating to wipe out the earth of humans, or even kill half of them... and we're talkign about devestation mankind has never even gotten close to witnessing...