Iridium and the Periodic Table of Death
An asteroid as large as 50 miles across hits what we now call the Yucatan, vaporizes in the 20,000-degree heat caused by the energy of the collision, catches pretty much everything on fire for 100s of miles, creates tsunamis as tall as the Eiffel tower, pitches the world into darkness for a year because of debris and dust thrown into the sky, and completely wipes out the dinosaurs.