Geological Cataclysm - The Chixulub meteor impact

When I was growing up, everyone knew about dinosaurs and their sudden extinction.  No archaeologist or geologist could come up with a valid explanation of what caused that extinction.  All anyone knew was that the Mesozoic Era abruptly ended and the Cenozoic Era ("The Age of Mammals") began.  Dinosaurs were the dominant terrestrial vertebrate for 135 million years - and then one day, pffft... they were gone.  But why???