The demise of the dinosaurs is the world's ultimate who-dunit. Was it a comet or asteroid impact? Volcanic eruptions? Climate change? All of the above? None of the above? In an attempt to resolve the issue, scientists have now determined the most precise dates yet for the dinosaur extinction 66 million years ago and for the well-known Chicxulub impact that occurred around the same time. The dates are so close, the researchers say, that they now believe the asteroid, if not wholly responsible for the global extinction, at least dealt the dinosaurs their death blow. It is now believed that the dramatic climate variation over the previous million years, including a sustained series of volcanic eruptions in India that produced the extensive Deccan Traps and long cold snaps amidst a general Cretaceous hothouse environment, probably brought many creatures to the brink of extinction. In the end, the impact kicked them over the edge.