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Uploaded on Jun 28, 2008
June 30 marks the 100th anniversary of a huge mid-air explosion that flattened hundreds of square miles of forests in Siberia. Recent computer simulations show it might have been a smaller near-earth object than previously theorized -- and thus the kind that hits Earth more frequently. Learn more at nytimes.com/dotearth and sandia.gov (video courtesy of Sandia National Lab)