Any third grader can tell you what killed the dinosaurs: an asteroid that smashed into Earth 66 million years ago, obliterating T. Rex, Triceratops, and Velociraptor, and paving the way for mammals to thrive.
But that theory was wildly controversial when first introduced in 1980 by Berkeley Nobel laureate Luis Alvarez and his son, Walter, a UC Berkeley paleogeologist. Their idea plunged the paleontology community into decades of acrimonious debate before it became the accepted explanation. Now the theory is being challenged once again. Read more about A Smoking Gun: The Asteroid that Killed the Dinosaurs May Have Had Help »