Dinosaurs Were Already In Decline Before Asteroid Wiped Them Out – New Research By Fabien Condamine 07/05/21 AT 12:52 AM Some 66 million years ago, on the Yucatán peninsula in Mexico, a 12 kilometre-wide asteroid crashes to Earth. The impact causes an explosion whose magnitude is hard to imagine today – several billion times more powerful than the atomic bomb dropped on Hiroshima. Most of the animals on the American continent are killed immediately. The impact also triggers worldwide tsunamis. Tons and tons of dust are ejected into the atmosphere, plunging the planet into darkness. This “nuclear winter” causes the extinction of many plant and animal species.