You may have seen the remarkable footage this morning of the meteor strikes in Russia that reportedly injured more than 750 people. The New York Times is reporting the fragments were from a 10-ton meteor that exploded and evaporated at a height of around 20 to 30 miles above the earth.
If you haven’t seen it, here is one of the videos posted to YouTube:
[youtube http://www.youtube.com/watch?v=iCawTYPtehk&w=560&h=315]

You may be wondering how big a fragment needs to be to produce significant damage on the ground. Check out 12.091 Basics of Impact Cratering & Geological, Geophysical, Geochemical, Environmental Studies of Some Impact Craters of the Earth to learn more about the science behind these spectacular and dangerous (but fortunately rare) occurrences.