While most of us were sleeping, an asteroid passed within 154,000 miles of Earth -- inside the moon's orbit. Another is expected to pass within 49,000 miles this afternoon.
The table below shows the potential damage to earth from an asteroid impact. As you move from left to right, the size of the rock gets bigger as does the potential destruction. The orange area indicates extinction.
A larger image of the table above can be found here. Here's a link to images from the Catalina Sky Survey at the University of Arizona-Tucson.
The interesting thing about this event is that the asteroids weren't discovered until last Sunday.