Space rocks thrown at Earth.

The recent space rock sizes. The one that hit Russia, and the other bigger one (asteroid 2012 DA14)  that fortunately passed us.  Either way, if the little one didn't blow up high in the atmosphere and hit Chelyabinsk directly it would have been a major disaster - more than just broken windows and confused Russians with their car cameras.  If the big one smacked us.....well, you just guess!