NASA says that large meteors -- several hundred to a few thousand feet wide -- hit the Earth every 50 to 100 thousand years. Dr. Ted Bryant and his colleagues disagree; they think such massive impacts happen much more often. And this group of scientists may have found signs that a meteor hit the ocean and produced a mega-tsunami that devastated Australias coastline -- only 500 years ago. National Geographic joins the team as they scour the coastline and the ocean floor trying to prove that cosmic impacts, and the mega-tsunamis that result, have happened far more frequently, and much more recently, than anyone ever thought.
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