Possible life extinction in the next asteroid collision to earth?

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Last 2002 or somewhat 2003,an asteroid almost hit our planet earth.We are very lucky that in some way the asteroid lost track and didn't hit earth..but sometime in future,I've read 2012,an asteroid the size of the moon will direclty hit our planet.. Eversince I've read about this,I kept thinking and thinking if life extinction will happen again like what happened in the past era of the dinosaurs...yikes scary thought!! Do you guys think it's really possible?I mean 2012 is like 3 years away..